Light

The topic of evolutionary mismatch with regard to light can be clearly divided into two broad subcategories: a deficiency of natural light and an excess of artificial light. There has, in fact, been in recent decades a significant amount of scientific investigation into the beneficial health effects of sunlight exposure and the deleterious effects of artificial light, yet many of these findings have not become popularized nor have they been explicitly understood within the context of evolutionary mismatch theory. The novel usage of electronic devices, such as televisions and smartphones, especially after sunset, negatively affects the amount and quality of sleep through various mechanisms such as by affecting melatonin production and dysregulation of the body’s circadian rhythm, which has further ramifying health effects. Conversely, human beings now spend significantly less time outdoors exposed to sunlight. Emerging evidence has shown that sunlight irradiation provides a suite of positive health effects and is an integral component of the complex environment for which humans adapted to. The lack of sun exposure in modern humans causes a serious disruption to health. These mismatches could possibly be corrected by modifying our use of artificial light, increasing exposure to natural light, and reconsidering our usage of sunscreen, clothing, and even glass windows.

Artificial Light

“…we commonly think of light as a primarily visual medium, our way for perceiving the world around us. However, light exposure serves another function, affecting a large range of physiological and behavioral parameters, including sleep and alertness. With the introduction and development of artificial light, we have progressively changed our lifestyle, extending our daylight hours beyond nature, to provide an environment conducive to self-fulfillment, and subconsciously exposing ourselves repeatedly to luminance pollution. This phenomenon has been exacerbated with the boom in new light-emitting technologies such as smartphones and tablets. Unfortunately, there are detrimental costs, resulting in the impairment of the sleep–wake architecture, which leads to an increased incidence of circadian disorders, insomnia, daytime sleepiness, mood alteration, and poorer cognitive performance” [20]

“The increase of artificial light at night (ALAN) in cities has altered the natural light levels in the nocturnal environment and extended human activities into the usually dark hours. It has been estimated that more than 80% of the world population (99% of the population from the United States and Europe) and almost one-fifth of the world terrain is under light-polluted skies that suffer from an excessive, misdirected, or obtrusive artificial (usually outdoor) light.” [23]

“The use of light-emitting electronic devices for reading, communication, and entertainment has greatly increased recently… the use of these devices before bedtime prolongs the time it takes to fall asleep, delays the circadian clock, suppresses levels of the sleep-promoting hormone melatonin, reduces the amount and delays the timing of REM sleep, and reduces alertness the following morning. Use of light-emitting devices immediately before bedtime also increases alertness at that time, which may lead users to delay bedtime at home… the use of portable light-emitting devices immediately before bedtime has biological effects that may perpetuate sleep deficiency and disrupt circadian rhythms, both of which can have adverse impacts on performance, health, and safety.” [27]

“We found that access to electricity in traditionally hunter-gatherer Toba/Qom communities is associated with later bedtimes and sleep onsets but not with later sleep-offset or rise times, leading to a shorter daily sleep duration than in individuals without access to electricity. This difference in sleep timing between the 2 communities also differed with season, with the community who had access to electricity sleeping approximately 40 min less in summer and an hour less in winter than the community without electricity. Examination of light levels in the 2 groups revealed that individuals in the community with access to electricity were exposed to brighter light intensities during the winter evenings, suggesting that their later sleep onset and shorter sleep duration are the result of their access to electric light. Similarly, a recent report of modern humans living in Stone Age conditions for 2 months found that the participants extended their time in bed and duration of sleep by approximately 90 min, with the majority of the extension achieved by earlier bedtimes.” [25]

“…studies show clearly that being exposed to light, especially blue light, at night is disruptive and that screen use at night may increase our tendency to snack on sugary foods and disrupt our ability to process that sugar…” [18]

‘The short-wavelength blue light, emitted by the screens we watch, damages the duration, and even more so, the quality of our sleep.’
“…our study shows that it is not the screens themselves that damage our biological clock, and therefore our sleep, but the short-wave blue light that they emit.” 
[21]

“Presence of a TV in a child’s bedroom and TV viewing have been linked to shorter sleep duration, later bedtimes, and other dimensions of sleep.TV viewing is a risk factor for weight gain, decreased academic achievement, and behavioral problems”
“…
[devices] held near the face… may delay melatonin release more strongly than TV light, which decays with distance.” [32]

“‘Limiting the amount of time that we spend in front of screens at night is, for now, the best measure to protect ourselves from the harmful effects of blue light. In case it is necessary to be exposed to devices at night, I would recommend the use of apps and night mode features on the devices, which turn the screens more orange and less blue or the use of blue light filtering googles that are already available in the market.'” [18]

Natural Light

“In the early 20th century, people went against evolution by going indoors during the day to work, which drastically decreased their daily amount of… vitamin D3. With the addition of larger buildings and sky scrappers, people created an unnatural UV barrier when windows were developed and used in abundance. The UV barrier created by window glass divided UVB from UVA, so that the vitamin D making UVB was excluded from our indoor working environment; only the vitamin D-breaking and DNA-mutating UVA was included. Because this unnatural UV environment existed for decades in buildings and cars, CMM [Cutaneous malignant melanoma] began to steadily increase about 20–30 years later in the mid-1930s.”
“Indoor workers go to and from work five days a week, usually before 9 a.m. and after 4 p.m., respectively, when the solar UVB is negligible, so that indoor workers hardly make any vitamin D3 commuting during the workweek and work year. Meanwhile, people can be exposed to UVA passing through the windows of their cars, which can break down vitamin D3.”
“… outdoor workers have a lower incidence of CMM compared to indoor workers.”
“…(CMM) has been increasing at a steady exponential rate in fair-skinned, indoor workers since before 1940. A paradox exists between indoor and outdoor workers because indoor workers get three to nine times less solar UV (290–400 nm) exposure than outdoor workers get, yet only indoor workers have an increasing incidence of CMM.”
“Besides breaking down vitamin D, indoor solar UVA window exposures can cause detrimental biological effects. For example, UVA1 (341–400 nm) radiation can cause oxidative stress, damage to organelles, red blood cell lysis, humoral immune suppression and photoaging.”
“…an all-year-tan is protective against melanoma, and outdoor workers, who get three to nine times the erythemally effective UV dose that indoor workers get have a significantly lower incidence of melanoma.”
“…outdoor activities in childhood decrease the incidence of melanoma (excluding sunburns) and there is no ‘’critical period,’ such as childhood, where intense exposures contribute more towards the induction of melanoma. In fact, some studies found that sunburns throughout life are an important risk factor for melanoma, while low level solar UV exposures are protective.”
“UVB initiates CMM when normal people are overexposed and this usually happens when they have minimal clothing on, exposing most of their body to intense sunlight. They wear clothes at work covering these body sites, so that when and if, they do go outside they cannot make vitamin D3 locally in the covered skin that was previously exposed. In addition, due to its longer wavelengths, UVA penetrates clothing much better than UVB and clothing prevents the formation of previtamin D3”
“UVB-absorbing sunscreens are associated with a significant increased risk of melanoma in humans.” 
[24]

“Sunburn in childhood and increased sun exposure during annual holidays in sunny areas should be avoided. In contrast, outdoor activities in childhood, including soccer and gardening, should be encouraged because they are associated with a lower risk of melanoma formation.” [28]

[Researchers] argue that what made the people with high vitamin D levels so healthy was not the vitamin itself. That was just a marker. Their vitamin D levels were high because they were getting plenty of exposure to the [sun].”
“…when [a researcher] exposed volunteers to the equivalent of 30 minutes of summer sunlight without sunscreen, their nitric oxide levels went up and their blood pressure went down. Because of its connection to heart disease and strokes, blood pressure is the leading cause of premature death and disease in the world, and the reduction was of a magnitude large enough to prevent millions of deaths on a global level.”
“…outdoor workers have half the melanoma rate of indoor workers. Tanned people have lower rates in general. “The risk factor for melanoma appears to be intermittent sunshine and sunburn, especially when you’re young,” says Weller. “But there’s evidence that long-term sun exposure associates with less melanoma.””
“‘Avoidance of sun exposure is a risk factor of a similar magnitude as smoking, in terms of life expectancy.'”
[Research] results clearly showed that the reason people in sunnier climes have lower blood pressure is as simple as light hitting skin.”
“Vitamin D now looks like the tip of the solar iceberg. Sunlight triggers the release of a number of other important compounds in the body, not only nitric oxide but also serotonin and endorphins. It reduces the risk of prostate, breast, colorectal, and pancreatic cancers. It improves circadian rhythms. It reduces inflammation and dampens autoimmune responses. It improves virtually every mental condition you can think of.”
“All early humans evolved outdoors beneath a tropical sun. Like air, water, and food, sunlight was one of our key inputs. Humans also evolved a way to protect our skin from receiving too much radiation—melanin, a natural sunscreen. Our dark-skinned African ancestors produced so much melanin that they never had to worry about the sun.”
“As humans migrated farther from the tropics and faced months of light shortages each winter, they evolved to produce less melanin when the sun was weak, absorbing all the sun they could possibly get. They also began producing much more of a protein that stores vitamin D for later use. In spring, as the sun strengthened, they’d gradually build up a sun-blocking tan. Sunburn was probably a rarity until modern times, when we began spending most of our time indoors.”
“People of color rarely get melanoma. The rate is 26 per 100,000 in Caucasians, 5 per 100,000 in Hispanics, and 1 per 100,000 in African Americans. On the rare occasion when African Americans do get melanoma, it’s particularly lethal—but it’s mostly a kind that occurs on the palms, soles, or under the nails and is not caused by sun exposure.”
“At the same time, African Americans suffer high rates of diabetes, heart disease, stroke, internal cancers, and other diseases that seem to improve in the presence of sunlight, of which they may well not be getting enough. Because of their genetically higher levels of melanin, they require more sun exposure to produce compounds like vitamin D, and they are less able to store that vitamin for darker days.”
“… early sunscreen formulations were disastrous, shielding users from the UVB rays that cause sunburn but not the UVA rays that cause skin cancer. Even today, SPF ratings refer only to UVB rays, so many users may be absorbing far more UVA radiation than they realize. Meanwhile, many common sunscreen ingredients have been found to be hormone disruptors that can be detected in users’ blood and breast milk.” 
[34]

“Whereas skin cancer is associated with too much UVR [UV radiation] exposure, other cancers could result from too little. Living at higher latitudes increases the risk of dying from Hodgkin lymphoma, as well as breast, ovarian, colon, pancreatic, prostate, and other cancers, as compared with living at lower latitudes.”
“When people are exposed to sunlight or very bright artificial light in the morning, their nocturnal melatonin production occurs sooner, and they enter into sleep more easily at night. Melatonin production also shows a seasonal variation relative to the availability of light, with the hormone produced for a longer period in the winter than in the summer. The melatonin rhythm phase advancement caused by exposure to bright morning light has been effective against insomnia, premenstrual syndrome, and seasonal affective disorder (SAD).”
“The melatonin precursor, serotonin, is also affected by exposure to daylight. Normally produced during the day, serotonin is only converted to melatonin in darkness. Whereas high melatonin levels correspond to long nights and short days, high serotonin levels in the presence of melatonin reflect short nights and long days (i.e., longer UVR exposure). Moderately high serotonin levels result in more positive moods and a calm yet focused mental outlook. Indeed, SAD has been linked with low serotonin levels during the day as well as with a phase delay in nighttime melatonin production.”
“For people in jobs in which sunlight exposure is limited, full-spectrum lighting may be helpful. Sunglasses may further limit the eyes’ access to full sunlight, thereby altering melatonin rhythms. Going shades-free in the daylight, even for just 10–15 minutes, could confer significant health benefits.” 
[36]

“For all practical purposes, vitamin D does not naturally occur in foodstuffs that humans eat. There are exceptions, such as oily fish and fish liver oil; however, for the most part, vitamin D does not naturally exist in significant amounts in the human food chain. The fact is, from an evolutionary standpoint, humans did not require vitamin D in their food supply, because, over millions of years humans, along with many animal species, evolved a photosynthetic mechanism in their skin to produce large amounts of vitamin D-3. Thus, our skin is part of the vitamin D endocrine system, and vitamin D-3 is really a preprohormone.”
“Approximately 50,000 y ago, small bands of people, almost certainly darkly pigmented, migrated gradually from sub-Saharan Africa to eventually populate more northern latitudes. This migration resulted in a profound evolutionary adaptation, a gradient in skin pigmentation loss to the point of almost total depigmentation as evidenced by northern European populations. Why would this dramatic change have occurred so rapidly? The most obvious answer is to maximize the limited sunlight exposure as occurs when moving north from the equator. Darkly pigmented individuals in an equatorial environment literally would be bathed in intense sunlight year round, and thus, vitamin D-3 production would not be a problem. However, as these darkly pigmented individuals migrated to a northern sun-restricted environment, they would rapidly become vitamin D depleted, with the resulting mobility and reproductive problems associated with deficiency. For humans to survive in this new northern environment, skin depigmentation had to occur. Eskimos are an exception to this, because they retain significant pigmentation; however, their migration from Asia was relatively recent, and the Eskimos’ diet is unique in that it contains significant levels of vitamin D-3 due to the fat and oily fish content.”
“Given the results of these recent scientific studies that evaluated high-dose vitamin D supplementation, it appears that the current DRI
[Dietary Reference Intake] for adults are woefully inadequate, misleading, and potentially harmful, placing individuals at undue risk for a number of chronic diseases. The current adult dietary recommendations of 200–600 IU/d are extraordinarily low compared with endogenous production during sun exposure. Reexamination of the requirements for vitamin D is clearly merited and may likely reveal the need for vitamin D intakes exceeding 2000 IU/d for adults.” [35]

“‘…there are only four prospective studies that examine sunscreen’s role in preventing skin cancer, and none of these studies examine the efficacy of sunscreen in preventing skin cancer in otherwise healthy individuals.'”
“…former FDA commissioner Robert Califf and the editor in chief of JAMA Dermatology, Kanade Shinkai, suggested that our cultural certainty about sunscreen is unearned. ‘Sunscreen users reasonably presume that companies that manufacture and sell sunscreens have conducted basic studies to support the safety and effectiveness of their products and that the medical profession would demand high-quality evidence,’ they wrote, adding that despite decades of widespread use: ‘[S]unscreens have not been subjected to standard drug safety testing.'”

“The first record of sun protection began with the Egyptians, who used ingredients such as rice bran, jasmine, and lupine. Though they did not understand the harmful effects the sun has on the skin, they did understand the concept of tanning. In a culture where lighter skin was more desirable, the purpose of their sunscreen was solely cosmetic. It has only recently been discovered that rice bran absorbs UV light, jasmine helps repair DNA, and lupine lightens skin. Other cultures have tried their luck at sun protection with varying success. The ancient Greeks used olive oil. Some Native American tribes used Tsuga canadensis, a type of pine needle, which was is also effective in soothing sunburns. It is surprising that these cultures were able to formulate sunscreens long before the cause of sun damage was understood. In the realm of sun protection, our ancient predecessors proved to be far ahead of their time.” [38]

Conclusion

The evidence seems to clearly suggest that artificial light has negative health consequences, so it seems optimal to adjust the duration, brightness, and even colour of the artificial light that is used. We can do this by limiting screen time, using applications and technology which adjust brightness and colour, such as computer software and adaptive light bulbs, and maybe even consider the usage of glasses which alter brightness and, or colour after dark. Equally, it is important to reconsider the quantity of our exposure to sunlight in the daytime and perhaps reduce our usage of sunscreen, sunglasses, and clothing. It seems that it is currently unknown whether Vitamin D is the sole mechanism by which sun exposure confers health benefits, whether it is one of multiple mechamisms, or whether there are other mechanisms currently undiscovered. Furthermore, the differential health effects of different types of Vitamin D, such as the supplementation form, the foodstuff form, and the endogenous form, are not yet fully known. As such, it seems most prudent to continue exposing oneself to sunlight, as this is accordant with the underlying theory of evolutionary mismatch.

More Information

“A new study demonstrates that just one hour of exposure to blue light at night — the kind of light produced by the screens of our many devices — raises blood sugar levels and increases sugar consumption in male rats.”

“Previous research has shown a strong correlation between obesity and the levels of artificial light at night. Much of the artificial light we are now exposed to comes from LED lights and LED screens, which emit high levels of blue light. Retinal cells of the eye are sensitive to this blue light and directly convey information to areas of the brain that regulate appetite.”

“The authors found that after only one hour of nocturnal blue light exposure, glucose tolerance was altered in male rats, a warning sign of pre-diabetes.”

“To investigate what happens with appetite control and food choice after exposure to blue light at night, the rats were given the option to choose among a nutritionally balanced food (standard rodent food), water, lard, and sugar water. After the exposure to blue light, they observed that the male animals drank more sugar that night than during the nights with no blue light exposure.”

[18]

“Exposure to increasing amounts of artificial light during the night may contribute to the high prevalence of reported sleep dysfunction.”

“Subjects (ages 17–42, n  = 21) wore short wavelength‐blocking glasses prior to bedtime for 2 weeks.”

“The use of short wavelength‐blocking glasses at night increased subjectively measured sleep quality and objectively measured melatonin levels and sleep duration, presumably as a result of decreased night‐time stimulation of ipRGC s [intrinsically photosensitive retinal ganglion cells]. Alterations in the ipRGC ‐driven pupil response suggest a shift in circadian phase. Results suggest that minimising short wavelength light following sunset may help in regulating sleep patterns.”

[19]

“In mammals, light exerts pervasive effects on physiology and behavior in two ways: indirectly through clock synchronization and the phase adjustment of circadian rhythms, and directly through the promotion of alertness and sleep, respectively, in diurnal and nocturnal species”

“In mice, blue light acutely causes behavioral arousal, whereas green wavelengths promote sleep.”

“…these findings stress the need to understand how best to adapt the color spectrum of light to our needs and to take this into account for the design of daily lighting concepts—a key challenge for today’s society, especially with the emergence of LED light technology.”

“Considering societal implications, with the development of LED and progressive switching from fluorescent or other light devices to this newer technology, we are increasingly exposed to non-homogeneous spectra of light. Thus, the possibility to balance light wavelength composition in favor of alertness or sleep maintenance would allow the adaptation of our illuminated surroundings to our needs, with reservation to the fact that light can also have indirect effects through phase shifting of circadian rhythms. This type of spectral management could be applicable to many daily living conditions, far beyond simply the workplace or the home, allowing us to also better adapt to situations like transmeridian travel or shift-work, in addition to dealing with increasingly continuous screen exposure using modern media and other concomitants of life in modern society.”

[20]

“The short-wavelength blue light, emitted by the screens we watch, damages the duration, and even more so, the quality of our sleep. This is the conclusion of a new study undertaken by the University of Haifa and Assuta Sleep Clinic. The study also found that watching screens that emit red light does not cause damage, and sleep after exposure to it was similar to normal sleep. ‘The light emitted by most screens — computers, smartphones, and tablets — is blue light that damages the body’s cycles and our sleep,’ explains Prof. Abraham Haim from the University of Haifa, one of the authors of the study.”

“Previous studies have already shown that watching screens before going to sleep damages our sleep. It has also been found that exposure to blue light with wave lengths of 450-500 nanometers suppresses the production of melatonin, a hormone secreted at night that is connected with normal body cycles and sleep.”

“On average, exposure to blue light reduced the duration of sleep by approximately 16 minutes. In addition, exposure to blue light significantly reduced the production of melatonin, whereas exposure to red light showed a very similar level of melatonin production to the normal situation. The researchers explain that the impaired production of melatonin reflects substantial disruption of the natural mechanisms and the body’s biological clock. Thus, for example, it was found that exposure to blue light prevents the body from activating the natural mechanism that reduces body temperature. ‘Naturally, when the body moves into sleep it begins to reduce its temperature, reaching the lowest point at around 4:00 a.m. When the body returns to its normal temperature, we wake up,’ Prof. Haim explains. ‘After exposure to red light, the body continued to behave naturally, but exposure to blue light led the body to maintain its normal temperature throughout the night — further evidence of damage to our natural biological clock.'”

“The most significant finding in terms of the disruption of sleep was that exposure to blue light drastically disrupts the continuity of sleep. Whereas after exposure to red light (at both intensities) people woke up an average of 4.5 times (unnoticed awakenings), following exposure to weak blue light 6.7 awakenings were recorded, rising to as many as 7.6 awakenings following exposure to strong blue light. Accordingly, it is hardly surprising that the participants reported in the questionnaires that the felt more tired and in a worse mood after exposure to blue light.”

“…our study shows that it is not the screens themselves that damage our biological clock, and therefore our sleep, but the short-wave blue light that they emit.”

[21]

“Light is necessary for life, but prolonged exposure to artificial light is a matter of increasing health concern. Humans are exposed to increased amounts of light in the blue spectrum produced by light-emitting diodes (LEDs), which can interfere with normal sleep cycles. The LED technologies are relatively new; therefore, the long-term effects of exposure to blue light across the lifespan are not understood”

“Exposure of adult flies to 12 h of blue light per day accelerated aging phenotypes causing damage to retinal cells, brain neurodegeneration, and impaired locomotion.”

“Blue light induces expression of stress-responsive genes in old flies but not in young, suggesting that cumulative light exposure acts as a stressor during aging.”

“Natural light is essential for the entrainment of circadian clocks, which leads to temporal coordination of physiology and behavior. However, emerging evidence suggests that increased exposure to artificial light is a risk factor for sleep and circadian disorders.”

“Understanding the effects of blue light on various life processes is becoming an increasingly important health issue as humans are exposed to more blue-enriched LED illumination for most of the day, or even at night due to shift work and light pollution in large cities.”

“In this study, we demonstrate that daily exposure to 12 h of visible light in the blue part of the spectrum accelerates aging in Drosophila. Light causes not only retinal damage but also neurodegeneration in the central nervous system, which may be involved in the premature decline in climbing ability and early mortality. Our data also suggest that susceptibility to light increases with age and repetitive exposure to blue light induces the expression of stress-response genes.”

[22]

“The increase of artificial light at night (ALAN) in cities has altered the natural light levels in the nocturnal environment and extended human activities into the usually dark hours (Falchi et al. 2011). It has been estimated that more than 80% of the world population (99% of the population from the United States and Europe) and almost one-fifth of the world terrain is under light-polluted skies that suffer from an excessive, misdirected, or obtrusive artificial (usually outdoor) light (Cinzano et al. 2001; Falchi et al. 2011, 2016). Migration toward the light emitting diode (LED) technology in urban settings has resulted to an increase in ALAN and particularly an increase of the blue light spectrum due to the use of white LED as the new urban light standard (Kyba et al. 2017).”

“In 2007, the International Agency for Research on Cancer (IARC) concluded that shift work that involves circadian disruption is ‘probably carcinogenic to humans’ (IARC 2007). The epidemiological evidence mostly focused on breast cancer, but since 2007 studies on night shift have examined other cancers and several have identified modest increased risks for prostate cancer (Behrens et al. 2017), particularly among advanced tumors (Papantoniou et al. 2016). Several mechanisms related to the circadian system and exposure to light at night were examined by IARC involving suppression of melatonin production, alterations of sleep–activity patterns, and deregulation of circadian genes. Depending on light intensity and wavelength, exposure to ALAN may affect human health by decreasing the production and secretion of pineal melatonin (N-acetyl-5-methoxytriptamine), which is a hormone normally produced in the dark phase of the 24-h cycle (Brainard et al. 2001; Chang et al. 2014; Escofet and Bará 2015; Thapan et al. 2013). Melatonin is related to cancer through several pathways (IARC 2010; Korkmaz and Reiter 2008), including effects on estrogen-receptor positive human breast cancer cells (Hill et al. 2015). Studies in day and night shift workers have shown a delay in peak time and lower melatonin levels in night workers with mean urinary 6-sulfatoxymelatonin (aMT6s) levels of 10.9 ng/mg creatinine per hour compared with 15.4 in day workers (Papantoniou et al. 2014). Data showing similar patterns in the general population in relation to ALAN are limited. For example, subjects reading light-emitting devices (e.g., eBook) before sleeping compared with a printed book, took longer to fall asleep, had reduced evening sleepiness, reduced melatonin secretion, later timing of their circadian clock, and reduced next-morning alertness (Chang et al. 2015).”

“Findings from this large case–control study of two cancers that have been associated with circadian disruption and light at night during shift work provide some support for the influence of ALAN for the development of cancer in the general population. Men who reported the highest level of exposure to indoor ALAN were at greater risk of prostate cancer than men who reported no indoor illumination at night. Although both cancers were less likely among those in the highest versus lowest tertile of exposure to outdoor ALAN in the visible spectrum, outdoor ALAN in the blue-light spectrum, which is believed to be the most biologically relevant exposure, was positively associated with prostate cancer and, to a lesser extent, with breast cancer.”

https://ehp.niehs.nih.gov/doi/10.1289/EHP1837 Evaluating the Association between Artificial Light-at-Night Exposure and Breast and Prostate Cancer Risk in Spain (MCC-Spain Study)

[23]

“Cutaneous malignant melanoma (CMM) has been increasing at a steady exponential rate in fair-skinned, indoor workers since before 1940. A paradox exists between indoor and outdoor workers because indoor workers get three to nine times less solar UV (290–400 nm) exposure than outdoor workers get, yet only indoor workers have an increasing incidence of CMM.”

“Paradoxically, although outdoor workers get much higher outdoor solar UV doses than indoor workers get, only the indoor workers’ incidence of cutaneous malignant melanoma (CMM) has been increasing at a steady exponential rate since before 1940.”

“…indoor workers may be at a higher risk for getting melanoma because they make little vitamin D3 locally in the skin during their workweek and UVA window exposures can break down any vitamin D3 just formed in the skin or circulating through the capillaries.”

“Besides breaking down vitamin D, indoor solar UVA window exposures can cause detrimental biological effects. For example, UVA1 (341–400 nm) radiation can cause oxidative stress, damage to organelles, red blood cell lysis, humoral immune suppression and photoaging.”

“In the early 20th century, people went against evolution by going indoors during the day to work, which drastically decreased their daily amount of cutaneous vitamin D3 and, along with it, their blood levels. With the addition of larger buildings and sky scrappers, people created an unnatural UV barrier when windows were developed and used in abundance. The UV barrier created by window glass divided UVB from UVA, so that the vitamin D making UVB was excluded from our indoor working environment; only the vitamin D-breaking and DNA-mutating UVA was included. Because this unnatural UV environment existed for decades in buildings and cars, CMM began to steadily increase about 20–30 years later in the mid-1930s.”

“Indoor workers go to and from work five days a week, usually before 9 a.m. and after 4 p.m., respectively, when the solar UVB is negligible, so that indoor workers hardly make any vitamin D3 commuting during the workweek and work year. Meanwhile, people can be exposed to UVA passing through the windows of their cars, which can break down vitamin D3.”

“UVB-absorbing sunscreens are associated with a significant increased risk of melanoma in humans.”

“…an all-year-tan is protective against melanoma, and outdoor workers, who get three to nine times the erythemally effective UV dose that indoor workers get have a significantly lower incidence of melanoma.”

“…outdoor activities in childhood decrease the incidence of melanoma (excluding sunburns) and there is no ‘critical period,’ such as childhood, where intense exposures contribute more towards the induction of melanoma. In fact, some studies found that sunburns throughout life are an important risk factor for melanoma, while low level solar UV exposures are protective.”

“UVB initiates CMM when normal people are overexposed and this usually happens when they have minimal clothing on, exposing most of their body to intense sunlight. They wear clothes at work covering these body sites, so that when and if, they do go outside they cannot make vitamin D3 locally in the covered skin that was previously exposed. In addition, due to its longer wavelengths, UVA penetrates clothing much better than UVB and clothing prevents the formation of previtamin D3”

“…continuous, rather than intermittent, exposure may reduce the risk for getting CMM, as demonstrated by the lower incidence in outdoor workers.”

“Thus, when humankind went against evolution by working indoors during the day and created an artificial barrier (window glass) dividing UVB from UVA in their outdoor and indoor environments, respectively, they inadvertently increased their incidence of CMM”

“Ironically, some exposure to UVB may be important for protection against the promotion of CMM because vitamin D3 is produced in the skin and converted by melanoma cells to 1,25-dihydroxyvitamin D3 or calcitriol. Calcitriol then binds the VDR signaling for growth inhibition or cell death.”

“The seemingly paradoxical fact that outdoor workers get fewer melanomas than indoor workers get, in the absence of any other data, suggests that insufficiently maintained levels of vitamin D3 in the skin and indoor solar UVA exposures play a role in promoting CMM. Therefore, if vitamin D3 is present in high enough concentrations in the skin and the VDR receptor is fully functional in melanoma cells, growth arrest, cell cycle arrest, and repair of DNA damage or apoptotic cell death can occur reducing the incidence of CMM.”

[24]

“Access to electric light might have shifted the ancestral timing and duration of human sleep. To test this hypothesis, we studied two communities of the historically hunter-gatherer indigenous Toba/Qom in the Argentinean Chaco. These communities share the same ethnic and sociocultural background, but one has free access to electricity while the other relies exclusively on natural light. We fitted participants in each community with wrist activity data loggers to assess their sleep-wake cycles during one week in the summer and one week in the winter. During the summer, participants with access to electricity had a tendency to a shorter daily sleep bout (43 ± 21 min) than those living under natural light conditions. This difference was due to a later daily bedtime and sleep onset in the community with electricity, but a similar sleep offset and rise time in both communities. In the winter, participants without access to electricity slept longer (56 ± 17 min) than those with access to electricity, and this was also related to earlier bedtimes and sleep onsets than participants in the community with electricity. In both communities, daily sleep duration was longer during the winter than during the summer. Our field study supports the notion that access to inexpensive sources of artificial light and the ability to create artificially lit environments must have been key factors in reducing sleep in industrialized human societies.”

“The daily timing and amount of sleep has changed throughout human history, particularly as our species transitioned from nomadic hunter-gatherer groups to agricultural societies and, more recently, to industrialized ones (Ekirch, 2006). Whereas historical records depict that the onset of sleep at night coincided with the inexorable arrival of dusk, modern society has crafted a sleep schedule that is heavily influenced by protected, artificially lit environments. Whether natural or artificial, light is among the most important environmental factors regulating sleep. In humans, light induces alertness and entrains a master circadian clock that regulates the timing of sleep (de la Iglesia and Lee, 2014). Thus, the ability to control our own exposure to light through artificial means likely altered when we sleep and for how long”

“When we focused our comparison of light exposure between the 2 groups on the evening hours, we found that the NO-electricity group was exposed to light of higher intensity [during summer]… In contrast to the summer results, comparisons of light exposure during the winter evening hours revealed that individuals in the Electricity group were exposed to higher light intensities “

“…in both communities, longer sleep duration during the winter was associated with later sleep offsets and rise times, rather than with earlier bedtimes and sleep onsets”

“Importantly, the Toba/Qom community with access to electricity that we studied has remarkably less access to brightly artificially lit environments, appliances, eReaders, and sources of mass media than typical communities in industrialized societies (Chang et al., 2015); thus, the reduction of sleep we report likely underestimates the effect of electricity on human sleep.”

[25]

“In addition to its role in vision, light exerts strong effects on behavior. Its powerful role in the modulation of mood is well established, yet remains poorly understood. Much research has focused on the effects of light on circadian rhythms and subsequent interaction with alertness and depression. The recent discovery of a third photoreceptormelanopsin, expressed in a subset of retinal ganglion cells, allows major improvement of our understanding of how photic information is processed. Light affects behavior in two ways, either indirectly through the circadian timing system, or directly through mechanisms that are independent of the circadian system. These latter effects have barely been studied in regard to mood, but recent investigations on the direct effects of light on sleep and alertness suggest additional pathways through which light could influence mood. Based on our recent findings, we suggest that light, via melanopsin, may exert its antidepressant effect through a modulation of the homeostatic process of sleep. Further research is needed to understand how these mechanisms interplay and how they contribute to the photic regulation of mood. Such research could improve therapeutic management of affective disorders and influence the management of societal lighting conditions.”

[26]

“In the past 50 y, there has been a decline in average sleep duration and quality, with adverse consequences on general health. A representative survey of 1,508 American adults recently revealed that 90% of Americans used some type of electronics at least a few nights per week within 1 h before bedtime. Mounting evidence from countries around the world shows the negative impact of such technology use on sleep. This negative impact on sleep may be due to the short-wavelength–enriched light emitted by these electronic devices, given that artificial-light exposure has been shown experimentally to produce alerting effects, suppress melatonin, and phase-shift the biological clock.”

“Participants reading an [light-emitting] LE-eBook took longer to fall asleep and had reduced evening sleepiness, reduced melatonin secretion, later timing of their circadian clock, and reduced next-morning alertness than when reading a printed book. These results demonstrate that evening exposure to an LE-eBook phase-delays the circadian clock, acutely suppresses melatonin, and has important implications for understanding the impact of such technologies on sleep, performance, health, and safety.”

“Reading the LE-eBook was associated with decreased sleepiness in the evening. An hour before bedtime, study participants rated themselves as less sleepy… The following morning, however, the results for self-reported sleepiness were reversed, with participants feeling sleepier the morning after reading an LE-eBook the prior evening … Furthermore, not only did they awaken feeling sleepier, it took them hours longer to fully “wake up” and attain the same level of alertness than in the printed book condition.”

“We found that, compared with reading a printed book in reflected light, reading a LE-eBook in the hours before bedtime decreased subjective sleepiness, decreased EEG delta/theta activity, and suppressed the late evening rise of pineal melatonin secretion during the time that the book was being read. We also found that, compared with reading a printed book, reading an LE-eBook in the hours before bedtime lengthened sleep latency; delayed the phase of the endogenous circadian pacemaker that drives the timing of daily rhythms of melatonin secretion, sleep propensity, and REM sleep propensity; and impaired morning alertness. These results indicate that reading an LE-eBook in the hours before bedtime likely has unintended biological consequences that may adversely impact performance, health, and safety. The results of this study are of particular concern, given recent evidence linking chronic suppression of melatonin secretion by nocturnal light exposure with the increased risk of breast, colorectal, and advanced prostate cancer associated with night-shift work (for review, see ref. 10), which has now been classified as a probable carcinogen by the World Health Organization (1112). Moreover, the observation that the endogenous circadian melatonin phase was 1.5 h later when reading an LE-eBook compared with reading from a printed book suggests that using a light-emitting device in the hours before bedtime is likely to increase the risk of delayed sleep-phase disorder and sleep onset insomnia (13), especially among individuals living in society who self-select their bedtimes and wake times. Induction of such misalignment of circadian phase is likely to lead to chronic sleep deficiency”

[27]

“Sunburn in childhood and increased sun exposure during annual holidays in sunny areas should be avoided. In contrast, outdoor activities in childhood, including soccer and gardening, should be encouraged because they are associated with a lower risk of melanoma formation.”

[28]

Mixed Evidence

“In humans, short-wavelength light evokes larger circadian responses than longer wavelengths. This reflects the fact that melanopsin, a key contributor to circadian assessments of light intensity, most efficiently captures photons around 480 nm and gives rise to the popular view that “blue” light exerts the strongest effects on the clock. However, in the natural world, there is often no direct correlation between perceived color (as reported by the cone-based visual system) and melanopsin excitation. Accordingly, although the mammalian clock does receive cone-based chromatic signals, the influence of color on circadian responses to light remains unclear. Here, we define the nature and functional significance of chromatic influences on the mouse circadian system. Using polychromatic lighting and mice with altered cone spectral sensitivity (Opn1mwR), we generate conditions that differ in color (i.e., ratio of L- to S-cone opsin activation) while providing identical melanopsin and rod activation. When biased toward S-opsin activation (appearing ‘blue’), these stimuli reliably produce weaker circadian behavioral responses than those favoring L-opsin (‘yellow’). This influence of color (which is absent in animals lacking cone phototransduction; Cnga3−/−) aligns with natural changes in spectral composition over twilight, where decreasing solar angle is accompanied by a strong blue shift. Accordingly, we find that naturalistic color changes support circadian alignment when environmental conditions render diurnal variations in light intensity weak/ambiguous sources of timing information. Our data thus establish how color contributes to circadian entrainment in mammals and provide important new insight to inform the design of lighting environments that benefit health.”

“Our data above indicate that the twilight blue shift substantially attenuates circadian responses to light and thus imply that blue stimuli should be less effective at resetting the clock than equi-luminant yellow.”

“Accordingly, although we do not discount the idea that some animals use color to help entrainment under such conditions, it seems unlikely that this is the primary role of color input to the clock for most mammals. Instead, a more globally relevant potential benefit of using color is to compensate for stochastic fluctuations in the diurnal rhythm of light intensity, e.g., due to variations in cloud cover”

“These data thereby confirm that naturalistic variations in color substantially enhance the amplitude and stability of clock-driven behavioral rhythms when the diurnal variation in light intensity provides unreliable timing information.”

“Contrary to common beliefs, it is yellow rather than blue colors that have the strongest effect on the mammalian circadian system. This relationship aligns with natural shifts in the color of ambient illumination, detectable during twilight by mammals with di- and tri-chromatic visual systems. Accordingly, we show that this color signal supports robust and stable circadian-driven behavior in the natural world, where stochastic variations in light levels introduce ambiguity to intensity as a signal of time of day.”

“An especially pertinent question, however, is whether the effects of color described here extend to other mammals, such as humans. The qualitative relationship between sun position and blue-yellow color should be retained for any mammal capable of color vision, and theoretical studies suggest that color could aid circadian entrainment in humans. Existing evidence for color opponency in primate ipRGCs and melanopsin-dependent responses in man give further reasons to believe that the effects of color reported here could extend also to humans. To date, however, much of our current understanding of the spectral sensitivity of the human circadian system has been inferred based on acute ‘non-visual’ responses, such as melatonin suppression. Consistent with a very recent observation that S-cone selective modulations do not noticeably influence such responses, acute suppression of melatonin by light appears to be primarily driven by melanopsin. Such responses do not always provide a reliable proxy for circadian photosensitivity, however. Indeed, direct investigations of human circadian resetting reveal that low-intensity, short-wavelength light (460 nm) produces smaller responses than longer wavelength light (555 nm) of equivalent melanopic illuminance. These data are therefore consistent with the circadian effects of color we identify in mice.”

“Such an arrangement is potentially important for practical approaches intended to adjust the circadian impact of artificial light. Current approaches typically rely on manipulating the ratio of short- and long-wavelength light, achieving modest differences in melanopic illuminance at the expense of perceptible changes in color. As a result, stimuli with high melanopsin excitation appear ‘bluer’ (and vice versa). A strong prediction of our research is that these changes in color may oppose any benefits obtained from modulating melanopsin photon capture. Recent work indicates that melanopsin-directed modulations that lack perceptible difference in color exert beneficial effects. Our data now suggest that supplementing such approaches with color changes of the appropriate direction could be especially effective at modulating circadian responses.”

[29]

“Light plays a critical role in the regulation of numerous aspects of physiology and behaviour, including the entrainment of circadian rhythms and the regulation of sleep. These responses involve melanopsin (OPN4)-expressing photosensitive retinal ganglion cells (pRGCs) in addition to rods and cones. Nocturnal light exposure in rodents has been shown to result in rapid sleep induction, in which melanopsin plays a key role. However, studies have also shown that light exposure can result in elevated corticosterone, a response that is not compatible with sleep. To investigate these contradictory findings and to dissect the relative contribution of pRGCs and rods/cones, we assessed the effects of light of different wavelengths on behaviourally defined sleep. Here, we show that blue light (470 nm) causes behavioural arousal, elevating corticosterone and delaying sleep onset. By contrast, green light (530 nm) produces rapid sleep induction. Compared to wildtype mice, these responses are altered in melanopsin-deficient mice (Opn4-/-), resulting in enhanced sleep in response to blue light but delayed sleep induction in response to green or white light. We go on to show that blue light evokes higher Fos induction in the SCN compared to the sleep-promoting ventrolateral preoptic area (VLPO), whereas green light produced greater responses in the VLPO. Collectively, our data demonstrates that nocturnal light exposure can have either an arousal- or sleep-promoting effect, and that these responses are melanopsin-mediated via different neural pathways with different spectral sensitivities. These findings raise important questions relating to how artificial light may alter behaviour in both the work and domestic setting.”

“Light exerts profound effects on our physiology and behaviour, setting our biological clocks to the correct time and regulating when we are asleep and we are awake. The photoreceptors mediating these responses include the rods and cones involved in vision, as well as a subset of photosensitive retinal ganglion cells (pRGCs) expressing the blue light-sensitive photopigment melanopsin. Previous studies have shown that mice lacking melanopsin show impaired sleep in response to light. However, other studies have shown that light increases glucocorticoid release—a response typically associated with stress. To address these contradictory findings, we studied the responses of mice to light of different colours. We found that blue light was aversive, delaying sleep onset and increasing glucocorticoid levels. By contrast, green light led to rapid sleep onset. These different behavioural effects appear to be driven by different neural pathways. Surprisingly, both responses were impaired in mice lacking melanopsin. These data show that light can promote either sleep or arousal. Moreover, they provide the first evidence that melanopsin directly mediates the effects of light on glucocorticoids. This work shows the extent to which light affects our physiology and has important implications for the design and use of artificial light sources.”

“Here, we show that sleep induction and light aversion responses in mice are differentially affected by wavelength. Green light is associated with rapid sleep induction, whereas blue light results in an arousal response, characterised by reduced sleep, behavioural light aversion, and elevated plasma corticosterone. Notably we show that in melanopsin-deficient animals, these opposing effects of wavelength are abolished. As such, melanopsin-deficient animals show attenuated sleep induction under green light or enhanced sleep onset under blue light. These data suggest that the effects of nocturnal light exposure are more complex than first envisaged, and that sleep induction in rodents depends upon a balance between these arousal-promoting and sleep-promoting effects of light.”

“Given the established role of melanopsin in the regulation of sleep in response to light, we predicted that blue light would be most effective at inducing sleep in mice. To our surprise, we found that blue light was less effective, with a delayed sleep onset compared to other wavelengths. These findings appear to be due to a specific arousal-promoting response to blue light, which inhibits the normal sleep-promoting effects of light… By contrast, green light results in rapid sleep induction in the home cage or transient increases in exploratory behaviour in a novel environment”

“It is also possible to place our results into a broader ecological context. Around twilight, there is a relative enrichment of blue light across the dome of the sky [41]. This would result in a change in the balance between blue light- and green light-sensitive pathways (S6C Fig). The spectral sensitivity of the blue light-aversive pathways may act to delay mice emerging from their burrows during early dusk and encourage a retreat to their burrow at early dawn. Such responses may help reduce the risk of predation at dawn and dusk, when there is a conflicting requirement for exploratory activity and safety. By contrast, exposure to longer wavelengths (green or white light) during the day may serve to limit daytime activity during waking bouts and promote sleep.”

“Human studies have demonstrated an important role of light in the regulation of arousal. This involves activation of multiple brain areas involved in alertness, cognitive function, and melatonin production [4247]. These studies report an increased effect of short wavelength light (470 nm or lower) associated with the increased suppression of melatonin, reduction in subjective sleepiness, reduced reaction times, and changes in EEG power in the delta-theta frequency range [43,44,48]. Moreover, blue light exposure prior to sleep has been shown to reduce slow wave activity in the 0.75–5.5 Hz range in the first sleep cycle with a subsequent increase in the third sleep cycle. REM sleep duration during these cycles was also observed to be shortened [49]. These findings are consistent with recent studies on the effects of light-emitting devices on both melatonin rhythms and sleep latency [50]. These data suggest a key role of blue light exposure in inducing arousal and wakefulness in humans and are supported by our findings in mice. As C57BL/6 mice are naturally melatonin deficient [51], the mechanisms mediating this effect of blue light are unlikely to be melatonin dependent. However, our data suggest that despite the differences between nocturnal and diurnal species, light may play a similar alerting role in mice as has been shown in humans, providing a valuable animal model to study the effects of light on cognitive function [48]. Whilst the arousal-promoting effects of light are consistent with human data, the sleep-promoting effects of light may differ between nocturnal and diurnal species. Here, we show that despite the arousal-promoting effects of blue light, mice still eventually go to sleep in response to nocturnal light exposure. By contrast, in diurnal species, nocturnal light may be expected to promote wakefulness, which may therefore be potentiated rather than antagonised by the arousing effects of blue light.”

“In summary, here we show that light may have either arousal-promoting or sleep-promoting effects on mice, with corresponding changes in behaviour and molecular responses, including the regulation of adrenal corticosterone. These opposing effects of light are dependent upon wavelength, with blue and green light resulting in arousal and sleep, respectively. These coordinated responses appear to involve different neural pathways, which are both impaired in melanopsin-deficient mice. This results in a reduction in the arousal-promoting effects of blue light, as well as attenuated sleep-promoting responses to green light. In addition to providing the first demonstration of a role for melanopsin in the regulation of adrenal corticosterone, these findings challenge our existing understanding of the role of melanopsin in the regulation of sleep. Finally, the identification of a light-dependent arousal-promoting mechanism in mice provides a valuable animal model to study the effects of light on human cognitive brain function. With the increasing demands of the 24/7 society resulting in rising levels of both artificial lighting and shift work, there is an urgent need to understand the biological effects of artificial light on sleep versus alertness.”

[30]

“Increasing evidence suggests an important role for light in regulation of aging and longevity. UV radiation is a mutagen that can promote aging and decrease longevity. In contrast, NIR [near infrared light] light has shown protective effects in animal disease models. In invertebrates, visible light can shorten or extend lifespan, depending on the intensity and wavelength composition. Visible light also impacts human health, including retina function, sleep, cancer and psychiatric disorders. Possible mechanisms of visible light include: controlling circadian rhythms, inducing oxidative stress, and acting through the retina to affect neuronal circuits and systems. Changes in artificial lighting (e.g., LEDs) may have implications for human health. It will be important to further explore the mechanisms of how light affects aging and longevity, and how light affects human health.”

[31]

“Sleeping near a small screen, sleeping with a TV in the room, and more screen time were associated with shorter sleep durations. Presence of a small screen, but not a TV, in the sleep environment and screen time were associated with perceived insufficient rest or sleep. These findings caution against unrestricted screen access in children’s bedrooms.”

“Presence of a TV in a child’s bedroom and TV viewing have been linked to shorter sleep duration, later bedtimes, and other dimensions of sleep. TV viewing is a risk factor for weight gain, decreased academic achievement, and behavioral problems”

“Compared with TV, which involves passive observation, interactive media such as video games and smartphones may be more disruptive of sleep. Smartphones and other Internet-enabled small devices are particularly concerning, because they are portals to almost all content (eg, games, music, videos, Web sites, texts, and e-mail). Because these devices are held near the face, they may delay melatonin release more strongly than TV light, which decays with distance.”

“…children who slept near a small screen (compared with never) and children with a TV in their sleep environment (compared with those without) had shorter weekday sleep durations. Relationships between screens in the sleep environment and sleep curtailment were accounted for by later bedtimes, consistent with students having fixed weekday waketimes for school. Presence of a small screen but not a TV in the sleep environment was significantly related to perceived insufficient rest or rest or sleep in the past week. TV or DVD viewing and video or computer game playing were associated with shorter weekday sleep duration and perceived insufficient rest or sleep. Children with more screen time also had later bedtimes.”

“Among a diverse sample of Massachusetts fourth- and seventh-grade public school students, the presence of small screens and TVs in sleep environments and the use of TV or DVDs and video or computer games were associated with shorter weekday sleep duration. Children who slept near a small screen and those with more screen time were more likely to have perceived insufficient rest or sleep in the past week.”

[32]

“Compared with white light (4000 K), blue-enriched white light (17 000 K) improved the subjective measures of alertness (P<0.0001), positive mood (P=0.0001), performance (P<0.0001), evening fatigue (P=0.0001), irritability (P=0.004), concentration (P<0.0001), and eye discomfort (P=0.002). Daytime sleepiness was reduced (P=0.0001), and the quality of subjective nocturnal sleep (P=0.016) was improved under blue-enriched white light. When the participants’ expectation about the effect of the light treatments was entered into the analysis as a covariate, significant effects persisted for performance, alertness, evening fatigue, irritability, difficulty focusing, concentrating, and blurred vision.”

 Exposure to blue-enriched white light during daytime workhours improves subjective alertness, performance, and evening fatigue.”

[33]

“And they believed that most of us weren’t getting enough of it. This made sense. Vitamin D is a hormone manufactured by the skin with the help of sunlight. It’s difficult to obtain in sufficient quantities through diet. When our ancestors lived outdoors in tropical regions and ran around half naked, this wasn’t a problem. We produced all the vitamin D we needed from the sun.

But today most of us have indoor jobs, and when we do go outside, we’ve been taught to protect ourselves from dangerous UV rays, which can cause skin cancer. Sunscreen also blocks our skin from making vitamin D, but that’s OK, says the American Academy of Dermatology, which takes a zero-tolerance stance on sun exposure: ‘You need to protect your skin from the sun every day, even when it’s cloudy,’ it advises on its website. Better to slather on sunblock, we’ve all been told, and compensate with vitamin D pills.

“These rebels argue that what made the people with high vitamin D levels so healthy was not the vitamin itself. That was just a marker. Their vitamin D levels were high because they were getting plenty of exposure to the thing that was really responsible for their good health—that big orange ball shining down from above.”

“Weller’s doubts began around 2010, when he was researching nitric oxide, a molecule produced in the body that dilates blood vessels and lowers blood pressure. He discovered a previously unknown biological pathway by which the skin uses sunlight to make nitric oxide.

It was already well established that rates of high blood pressure, heart disease, stroke, and overall mortality all rise the farther you get from the sunny equator, and they all rise in the darker months. Weller put two and two together and had what he calls his ‘eureka moment’: Could exposing skin to sunlight lower blood pressure?

“Melanoma, the deadly type of skin cancer, is much rarer, accounting for only 1 to 3 percent of new skin cancers. And perplexingly, outdoor workers have half the melanoma rate of indoor workers. Tanned people have lower rates in general. ‘The risk factor for melanoma appears to be intermittent sunshine and sunburn, especially when you’re young,’ says Weller. ‘But there’s evidence that long-term sun exposure associates with less melanoma.'”

“So Lindqvist decided to look at overall mortality rates, and the results were shocking. Over the 20 years of the study, sun avoiders were twice as likely to die as sun worshippers.

There are not many daily lifestyle choices that double your risk of dying. In a 2016 study published in the Journal of Internal Medicine, Lindqvist’s team put it in perspective: ‘Avoidance of sun exposure is a risk factor of a similar magnitude as smoking, in terms of life expectancy.'”

“Weller’s largest study yet is due to be published later in 2019. For three years, his team tracked the blood pressure of 340,000 people in 2,000 spots around the U.S., adjusting for variables such as age and skin type. The results clearly showed that the reason people in sunnier climes have lower blood pressure is as simple as light hitting skin.”

“When I spoke with Weller, I made the mistake of characterizing this notion as counterintuitive. ‘It’s entirely intuitive,’ he responded. ‘Homo sapiens have been around for 200,000 years. Until the industrial revolution, we lived outside. How did we get through the Neolithic Era without sunscreen? Actually, perfectly well. What’s counterintuitive is that dermatologists run around saying, “Don’t go outside, you might die.”‘”

[34]

“The current adult recommendations for vitamin D, 200–600 IU/d [International units per day], are very inadequate when one considers that a 10–15 min whole-body exposure to peak summer sun will generate and release up to 20,000 IU vitamin D-3 into the circulation… Recent studies reveal that current dietary recommendations for adults are not sufficient to maintain circulating 25(OH)D [Vitamin D] levels at or above this level, especially in pregnancy and lactation.”

[35]

“Unlike other essential vitamins, which must be obtained from food, vitamin D can be synthesized in the skin through a photosynthetic reaction triggered by exposure to UVB radiation. The efficiency of production depends on the number of UVB photons that penetrate the skin, a process that can be curtailed by clothing, excess body fat, sunscreen, and the skin pigment melanin. For most white people, a half-hour in the summer sun in a bathing suit can initiate the release of 50,000 IU (1.25 mg) vitamin D into the circulation within 24 hours of exposure; this same amount of exposure yields 20,000–30,000 IU in tanned individuals and 8,000–10,000 IU in dark-skinned people.”

“The first humans evolved in equatorial Africa, where the direct angle of sunlight delivers very strong UVR most of the year. The gradual loss of protective fur may have created evolutionary pressure to develop deeply pigmented skin to avoid photodegradation of micronutrients and protect sweat glands from UVR-induced injury.”

“Over time, clothing became the norm in higher latitudes and then eventually a social attribute in many societies. By the 1600s, peoples in these regions covered their whole body, even in summertime. Many children who lived in the crowded and polluted industrialized cities of northern Europe developed rickets. By the late 1800s, approximately 90% of all children living in industrialized Europe and North America had some manifestations of the disease, according to estimates based on autopsy studies of the day cited by Holick in the August 2006 Journal of Clinical Investigation and the October 2007 American Journal of Public Health.

Doctors throughout Europe and North America began promoting whole-body sun-bathing to help prevent rickets. It was also recognized that wintertime sunlight in the temperate zone was too feeble to prevent rickets. For this reason, many children were exposed to UVR from a mercury or carbon arc lamp for one hour three times a week, which proved to be an effective preventive measure and treatment.

Around the time the solar solution to rickets gained widespread traction in medical circles, another historic scourge, tuberculosis (TB), was also found to respond to solar intervention. TB patients of all ages were sent to rest in sunny locales and generally returned in good health. Dermatology professor Barbara A. Gilchrest of Boston University School of Medicine says that, whereas sun exposure was shown to improve cutaneous TB, sanatorium patients with pulmonary TB likely responded as much or more to rest and good nutrition than to UVR. Nevertheless, a meta-analysis published in the February 2008 International Journal of Epidemiology found that high vitamin D levels reduce the risk of active TB (i.e., TB showing clinical symptoms) by 32%.

Almost overnight, as awareness of the sun’s power against rickets and TB spread, attitudes toward sun exposure underwent a radical shift. The suntan became valued in the Western world as a new status symbol that signified both health and wealth, as only the affluent could afford to vacation by the sea and play outdoor sports. Phototherapy quickly emerged as a popular medical treatment not only for TB, but also for rheumatic disorders, diabetes, gout, chronic ulcers, and wounds. The ‘healthy tan’ was in, and ‘sickly-looking’ pale skin was out.”

“Various studies have linked low 25(OH)D levels to diseases other than cancer, raising the possibility that vitamin D insufficiency is contributing to many major illnesses. For example, there is substantial though not definitive evidence that high levels of vitamin D either from diet or from UVR exposure may decrease the risk of developing multiple sclerosis (MS). Populations at higher latitudes have a higher incidence and prevalence of MS; a review in the December 2002 issue of Toxicology by epidemiology professor Anne-Louise Ponsonby and colleagues from The Australian National University revealed that living at a latitude above 37° increased the risk of developing MS throughout life by greater than 100%.”

“Whereas skin cancer is associated with too much UVR exposure, other cancers could result from too little. Living at higher latitudes increases the risk of dying from Hodgkin lymphoma, as well as breast, ovarian, colon, pancreatic, prostate, and other cancers, as compared with living at lower latitudes. A randomized clinical trial by Joan Lappe, a medical professor at Creighton University, and colleagues, published in the June 2007 issue of the American Journal of Clinical Nutrition, confirmed that taking 2–4 times the daily dietary reference intake of 200–600 IU vitamin D3 and calcium resulted in a 50–77% reduction in expected incidence rates of all cancers combined over a four-year period in post-menopausal women living in Nebraska.

Moreover, although excessive sun exposure is an established risk factor for cutaneous malignant melanoma, continued high sun exposure was linked with increased survival rates in patients with early-stage melanoma in a study reported by Marianne Berwick, an epidemiology professor at the University of New Mexico, in the February 2005 Journal of the National Cancer Institute. Holick also points out that most melanomas occur on the least sun-exposed areas of the body, and occupational exposure to sunlight actually reduced melanoma risk in a study reported in the June 2003 Journal of Investigative Dermatology.”

“…solely breastfed infants whose mothers were vitamin D deficient during pregnancy have smaller reserves of the nutrient and are at greater risk of developing rickets. Even in the sun-rich environment of the Middle East, insufficient vitamin D is a severe problem among breast-fed infants of women who wear a burqa (a traditional garment that covers the body from head to foot), as reported in the February 2003 Journal of Pediatrics.

Several recent reports indicate an increase in rickets particularly among breastfed black infants, though white babies also are increasingly at risk. A study in the February 2007 Journal of Nutrition concluded that black and white pregnant women and neonates in the northern United States are at high risk of vitamin D insufficiency, even when mothers take prenatal vitamins (which typically provide 100–400 IU vitamin D3).”

“In the context of inadequate sunlight or vitamin D insufficiency, some scientists worry that the emphasis on preventing skin cancers tends to obscure the much larger mortality burden posed by more life-threatening cancers such as lung, colon, and breast cancers. Many studies have shown that cancer-related death rates decline as one moves toward the lower latitudes (between 37°N and 37°S), and that the levels of ambient UVR in different municipalities correlate inversely with cancer death rates there. ‘As you head from north to south, you may find perhaps two or three extra deaths [per hundred thousand people] from skin cancer,’ says Vieth. ‘At the same time, though, you’ll find thirty or forty fewer deaths for the other major cancers. So when you estimate the number of deaths likely to be attributable to UV light or vitamin D, it does is not appear to be the best policy to advise people to simply keep out of the sun just to prevent skin cancer.’

To maximize protection against cancer, Grant recommends raising 25(OH)D levels to between 40 and 60 ng/mL. Research such as that described in Holick’s August 2006 Journal of Clinical Investigation article indicates that simply keeping the serum level above 20 ng/mL could reduce the risk of cancer by as much as 30–50%.

Cedric F. Garland, a medical professor at the University of California, San Diego, says that maintaining a serum level of 55–60 ng/mL may reduce the breast cancer rate in temperate regions by half, and that incidence of many other cancers would be similarly reduced as well. He calls this “the single most important action that could be taken by society to reduce the incidence of cancer in North America and Europe, beyond not smoking.” Moreover, these levels could be readily achieved by consuming no more than 2,000 IU/day of vitamin D3 at a cost of less than $20 per year and, unless there are contraindications to sunlight exposure, spending a few minutes outdoors (3–15 minutes for whites and 15–30 minutes for blacks) when the sun is highest in the sky, with 40% of the skin area exposed.

Holick, Vieth, and many other experts now make a similar daily recommendation: 4,000 IU vitamin D3 without sun exposure or 2,000 IU plus 12–15 minutes of midday sun. They say this level is quite safe except for sun-sensitive individuals or those taking medications that increase photosensitivity.

Gilchrest says some sunlight enters the skin even through a high-SPF sunscreen, so people can maximize their dermal vitamin D production by spending additional time outdoors while wearing protection. ‘Without the sunscreen, this same individual would be incurring substantially more damage to her skin but not further increasing her vitamin D level,’ she says.”

“A growing number of scientists are concerned that efforts to protect the public from excessive UVR exposure may be eclipsing recent research demonstrating the diverse health-promoting benefits of UVR exposure. Some argue that the health benefits of UVB radiation seem to outweigh the adverse effects, and that the risks can be minimized by carefully managing UVR exposure (e.g., by avoiding sunburn)…”

“As with MS, there appears to be a latitudinal gradient for type 1 diabetes, with a higher incidence at higher latitudes. A Swedish epidemiologic study published in the December 2006 issue of Diabetologia found that sufficient vitamin D status in early life was associated with a lower risk of developing type 1 diabetes. Nonobese mice of a strain predisposed to develop type 1 diabetes showed an 80% reduced risk of developing the disease when they received a daily dietary dose of 1,25(OH)D, according to research published in the June 1994 issue of the same journal. And a Finnish study published 3 November 2001 in The Lancet showed that children who received 2,000 IU vitamin D per day from 1 year of age on had an 80% decreased risk of developing type 1 diabetes later in life, whereas children who were vitamin D deficient had a fourfold increased risk. Researchers are now seeking to understand how much UVR/vitamin D is needed to lower the risk of diabetes and whether this is a factor only in high-risk groups.”

“There is also a connection with metabolic syndrome, a cluster of conditions that increases one’s risk for type 2 diabetes and cardiovascular disease. A study in the September 2006 issue of Progress in Biophysics and Molecular Biology demonstrated that in young and elderly adults, serum 25(OH)D was inversely correlated with blood glucose concentrations and insulin resistance. Some studies have demonstrated high prevalence of low vitamin D levels in people with type 2 diabetes, although it is not clear whether this is a cause of the disease or an effect of another causative factor—for example, lower levels of physical activity (in this case, outdoor activity in particular).”

“People living at higher latitudes throughout the world are at higher risk of hypertension, and patients with cardiovascular disease are often found to be deficient in vitamin D, according to research by Harvard Medical School professor Thomas J. Wang and colleagues in the 29 January 2008 issue of Circulation. ‘Although the exact mechanisms are poorly understood, it is known that 1,25(OH)D is among the most potent hormones for down-regulating the blood pressure hormone renin in the kidneys,’ says Holick. ‘Moreover, there is an inflammatory component to atherosclerosis, and vascular smooth muscle cells have a vitamin D receptor and relax in the presence of 1,25(OH)D, suggesting a multitude of mechanisms by which vitamin D may be cardioprotective.'”

“To determine the potential link betwen sun exposure and the protective effect in preventing hypertension, Rolfdieter Krause of the Free University of Berlin Department of Natural Medicine and colleagues exposed a group of hypertensive adults to a tanning bed that emitted full-spectrum UVR similar to summer sunlight. Another group of hypertensive adults was exposed to a tanning bed that emitted UVA-only radiation similar to winter sunlight. After three months, those who used the full-spectrum tanning bed had an average 180% increase in their 25(OH)D levels and an average 6 mm Hg decrease in their systolic and diastolic blood pressures, bringing them into the normal range. In constrast, the group that used the UVA-only tanning bed showed no change in either 25(OH)D or blood pressure.”

“As diurnal creatures, we humans are programmed to be outdoors while the sun is shining and home in bed at night. This is why melatonin is produced during the dark hours and stops upon optic exposure to daylight. This pineal hormone is a key pacesetter for many of the body’s circadian rhythms. It also plays an important role in countering infection, inflammation, cancer, and auto-immunity, according to a review in the May 2006 issue of Current Opinion in Investigational Drugs. Finally, melatonin suppresses UVR-induced skin damage, according to research in the July 2005 issue of Endocrine.

With our modern-day penchant for indoor activity and staying up well past dusk, nocturnal melatonin production is typically far from robust. ‘The light we get from being outside on a summer day can be a thousand times brighter than we’re ever likely to experience indoors,’ says melatonin researcher Russel J. Reiter of the University of Texas Health Science Center. ‘For this reason, it’s important that people who work indoors get outside periodically, and moreover that we all try to sleep in total darkness. This can have a major impact on melatonin rhythms and can result in improvements in mood, energy, and sleep quality.’

William Grant, who directs the Sunlight, Nutrition, and Health Research Center, a research and education organization based in San Francisco, suspects that sun exposure and higher 25(OH)D levels may confer protection against other illnesses such as rheumatoid arthritis (RA), asthma, and infectious diseases. ‘Vitamin D induces cathelicidin, a polypeptide that effectively combats both bacterial and viral infections,’ Grant says. ‘This mechanism explains much of the seasonality of such viral infections as influenza, bronchitis, and gastroenteritis, and bacterial infections such as tuberculosis and septicemia.’ For example, RA is more severe in winter, when 25(OH)D levels tend to be lower, and is also more prevalent in the higher latitudes. In addition, 25(OH)D levels are inversely associated with the clinical status of RA patients, and greater intake of vitamin D has been linked with lower RA risk, as reported in January 2004 in Arthritis & Rheumatism.”

“‘Current observations of widespread vitamin D insufficiency should not be attributed only to sun protection strategies,’ says [Robyn] Lucas. ‘Over the same period there is a trend to an increasingly indoor lifestyle, associated with technological advances such as television, computers, and video games.’ She says sun-safe messages remain important—possibly more so than ever before—to protect against the potentially risky high-dose intermittent sun exposure that people who stay indoors may be most likely to incur.”

“Exposure to both UVA and UVB radiation can have direct immunosuppressive effects through upregulation of cytokines (TNF-α and IL-10) and increased activity of T regulatory cells that remove self-reactive T cells. These mechanisms may help prevent autoimmune diseases.”

“Released in response to both UVA and UVB exposure, this potent neuropeptide modulates a number of cytokines and is linked with impaired induction of immunity and the development of immunologic tolerance. According to a report in the September 2007 issue of Photochemistry and Photobiology, mast cells (which mediate hypersensitivity reactions) play a critical role in CGRP-mediated immune suppression. This could help explain sunlight’s efficacy in treating skin disorders such as psoriasis.”

[36]

“The Ancient Egyptians were well aware of the dangers of the sun. Their landswere scorched with heat. Women protected their skin, preferring light skin todark in their cultural hierarchy of beauty (1). Recent discoveries written onpapyri and the walls of several tombs unearthed ingredients and formulationsin use in Ancient Egypt specifically addressing issues of sun damage to thehair and skin (2,3)…Tirmisor lupin extract was used to block the rays of the sun and is stillused to date to lighten the color of the skin…Yasmeenor jasmin was used to heal the sun-damaged skin. Recentevidence reveals that jasmin aids in DNA repair at the cellular level…Sobaror aloe was used to heal sun-damaged skin…Zaytoonor olive oil was used as a hydrating oil for both skin and hairdamaged by overexposure to the sunlight…Aquatic lotus oil was used for protection of the skin from the sun..Lozeor almond oil was applied before and after sun exposure to hydratethe sun-damaged skin, improving elasticity and texture…Calcite powder and clay were used as ultraviolet (UV) filters similar tothe modern day inorganic particulates zinc oxide and titanium dioxide..Rice bran extracts were used in sunscreen preparations. Today, gammaoryzanol extracted from rice bran has UV absorbing properties..A number of cosmetic ingredients were used to mask and protect theskin and hair from the ravishing rays of the sun (2,3). These includedkohl(to darken eyes in order to combat sunlight impairment to theretina in the glare of the desert sun), red ochre (to redden and imparta rosy glow in women’s makeup mimicking the effect of the sun onthe skin), and henna oil (to dye the lips and nails, darken the color ofthe hair and skin, and protect light skin from the sun). It is interestingto note that lawsone, the active principle of henna, was a Food andDrug Administration (FDA) Category I sunscreen molecule!”

[37]

“While it’s plausible that sunscreen prevents skin cancer… robust evidence to back that up is hard to come by. Such is the conclusion of a review study published in the Journal of the American Academy of Dermatology in February. ‘Sunscreen is a multibillion-dollar industry, and its efficacy in the prevention of skin cancer is often taken as fact,’ the authors note. ‘Despite this, there are only four prospective studies that examine sunscreen’s role in preventing skin cancer, and none of these studies examine the efficacy of sunscreen in preventing skin cancer in otherwise healthy individuals.'”

“…a recent study published in the Journal of the American Medical Association (JAMA) raised questions about the safety of various sunscreen ingredients. In a pilot study of 24 adults, scientists at the U.S. Food and Drug Administration (FDA) showed that four active ingredients commonly used in sunscreens — avobenzone, ecamsule, octocrylene, and oxybenzone — were absorbed into the bloodstream at high enough levels to trigger the need for additional safety studies.”

“Given the sun’s probable role in most skin cancers, though, it’s surprising that there isn’t stronger evidence that sunscreen prevents all forms of the disease. In the Journal of the American Academy of Dermatology review, the authors found only four randomized controlled trials conducted in the last four decades. The analysis found strong evidence that sunscreen prevented squamous cell, but not basal cell carcinomas, most likely because those cancers develop too slowly for studies to detect a trend, said lead author Reid Waldman, a dermatology resident at the University of Connecticut.

Only one study looked at melanoma, Waldman and his co-author found. Although that study is widely cited as proof that sunscreen halves the risk of melanoma, that’s misleading, Waldman told me. People given sunscreen and told to use it daily during the four years of the original trial had a 1.5 percent risk of developing melanoma 10 years later, compared to a 3 percent risk in those not given sunscreen or instructions — a difference that barely reached statistical significance.”

[39]

“High 25(OH)D concentrations were not associated with a lower risk of cancer, except colorectal cancer. Results from intervention studies did not show an effect of vitamin D supplementation on disease occurrence, including colorectal cancer. In 34 intervention studies including 2805 individuals with mean 25(OH)D concentration lower than 50 nmol/L at baseline supplementation with 50 μg per day or more did not show better results. Supplementation in elderly people (mainly women) with 20 μg vitamin D per day seemed to slightly reduce all-cause mortality. The discrepancy between observational and intervention studies suggests that low 25(OH)D is a marker of ill health. Inflammatory processes involved in disease occurrence and clinical course would reduce 25(OH)D, which would explain why low vitamin D status is reported in a wide range of disorders. In elderly people, restoration of vitamin D deficits due to ageing and lifestyle changes induced by ill health could explain why low-dose supplementation leads to slight gains in survival.”

[44]

Light Sources

[18] Blue light at night increases the consumption of sweets in rats

[19] Attenuation of short wavelengths alters sleep and the ipRGC pupil response

[20] Alerting or Somnogenic Light: Pick Your Color

[21] Blue light emitted by screens damages our sleep, study suggests 

[22] Daily blue-light exposure shortens lifespan and causes brain neurodegeneration in Drosophila

[23] Evaluating the Association between Artificial Light-at-Night Exposure and Breast and Prostate Cancer Risk in Spain (MCC-Spain Study)

[24] Increased UVA exposures and decreased cutaneous Vitamin D-3 levels may be responsible for the increasing incidence of melanoma

[25] Access to Electric Light Is Associated with Shorter Sleep Duration in a Traditionally Hunter-Gatherer Community

[26] Complex interaction of circadian and non-circadian effects of light on mood: Shedding new light on an old story

[27] Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness

[28] Outdoor activities in childhood: a protective factor for cutaneous melanoma? Results of a case–control study in 271 matched pairs

[30] Melanopsin Regulates Both Sleep-Promoting and Arousal-Promoting Responses to Light

[31] Effects of light on aging and longevity

[32] Sleep Duration, Restfulness, and Screens in the Sleep Environment

[33] Blue-enriched White Light in the Workplace Improves Self-Reported Alertness, Performance and Sleep Quality

[35] Circulating 25-Hydroxyvitamin D Levels Indicative of Vitamin D Sufficiency: Implications for Establishing a New Effective Dietary Intake Recommendation for Vitamin D

[36] Benefits of Sunlight: A Bright Spot for Human Health

[37] Page 4. Nadim S (2005). “Sunscreen Evolution”. In Shaath N (ed.). Sunscreens : regulations and commercial development (3 ed.). Boca Raton, Fl.: Taylor & Francis. ISBN 978-0824757946.

[38] The History of Sunscreen

[39] The Science Behind Sunscreen Isn’t as Strong as You Think

[40] Sunscreen Use and the Risk for Melanoma: A Quantitative Review

[41] Effect of Sunscreen Application Under Maximal Use Conditions on Plasma Concentration of Sunscreen Active Ingredients

[42] The role of sunscreen in the prevention of cutaneous melanoma and nonmelanoma skin cancer

[43] Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease

[44] Vitamin D status and ill health: a systematic review

Mixed Evidence:

[29] Cones Support Alignment to an Inconsistent World by Suppressing Mouse Circadian Responses to the Blue Colors Associated with Twilight

Essays:

[34] Is Sunscreen the New Margarine?

[39] The Science Behind Sunscreen Isn’t as Strong as You Think

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