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ron Health Perspect. 2008 Apr; 116(4): A160–A167.

doi :10.1289/ehp.116-a160

PMCID:

PMC2290997

PMID : 18414615

Benefits of Sunlight: A Bright Spot for Human Health

M. Nathaniel MeadCopyright and License information DisclaimerCopyright notice Publication of EHP lies in the public domain name & is therefore without copyright. All text from EHP may be reprinted freely. Use of materials published in EHP should be acknowledged ( for example, ? Reproduced with permission from Environmental Health Perspectives ? ) ; pertinent reference information should be provided for the article from which the material was reproduced. Articles from EHP, especially the News section, may contain photographs or illustrations copyrighted by other commercial organizations or individuals that may not be used without obtaining prior approval from the holder of the copyright .

Each day, Apollo’s fiery chariot makes its way across the sky, bringing life-giving light to the planet. For the ancient Greeks và Romans, Apollo was the god of medicine và healing as well as of sun và light — but Apollo could bring sickness as well as cure. Today’s scientists have come to a similarly dichotomous recognition that exposure to the ultraviolet radiation ( UVR ) in sunlight has both beneficial & deleterious effects on human health .Most public health messages of the past century have focused on the hazards of too much sun exposure. UVA radiation ( 95 – 97 % of the UVR that reaches Earth’s surface ) penetrates deeply into the hình mẫu, where it can contribute to giao diện cancer indirectly via generation of DNA-damaging molecules such as hydroxyl và oxygen radicals. Sunburn is caused by too much UVB radiation ; this size also leads to direct DNA damage & promotes various hình mẫu cancers. Both forms can damage collagen fibers, destroy vi ta min A in giao diện, accelerate aging of the giao diện, và increase the risk of giao diện cancers. Excessive sun exposure can also cause cataracts & diseases aggravated by UVR-induced immunosuppression such as reactivation of some latent viruses .However, excessive UVR exposure accounts for only 0.1 % of the total global burden of disease in disability-adjusted life years ( DALYs ), according to the 2006 World Health Organization ( WHO ) báo cáo The Global Burden of Disease Due to Ultraviolet Radiation. DALYs measure how much a person’s expectancy of healthy life is reduced by premature death or disability caused by disease. Coauthor Robyn Lucas, an epidemiologist at the National Centre for Epidemiology & Population Health in Canberra, nước Australia, explains that many diseases linked to excessive UVR exposure tend to be relatively benign — apart from malignant melanoma — & occur in older age groups, due mainly to the long giật between exposure & manifestation, the requirement of cumulative exposures, or both. Therefore, when measuring by DALYs, these diseases incur a relatively low disease burden despite their high prevalence .In contrast, the same WHO báo cáo noted that a markedly larger annual disease burden of 3.3 billion DALYs worldwide might result from very low levels of UVR exposure. This burden subsumes major disorders of the musculoskeletal system & possibly an increased risk of various autoimmune diseases & life-threatening cancers .The best-known benefit of sunlight is its ability to boost the body’s vi ta min D supply ; most cases of vi ta min D deficiency are due to lack of outdoor sun exposure. At least 1,000 different genes governing virtually every tissue in the body toàn thân are now thought to be regulated by 1,25 – dihydroxyvitamin D3 ( 1,25 [ OH ] D ), the active khung of the vi ta min, including several involved in calcium metabolism & neuromuscular và immune system functioning .Although most of the health-promoting benefits of sun exposure are thought to occur through vi ta min D photosynthesis, there may be other health benefits that have gone largely overlooked in the debate end how much sun is needed for good health [ see “ Other Sun-Dependent Pathways, ” p. A165 ]. As for what constitutes “ excessive ” UVR exposure, there is no one-size-fits-all answer, says Lucas : “ ‘ Excessive ’ really means inappropriately high for your giao diện type under a particular màn chơi of ambient UVR. ”

Vitamin D Production

Unlike other essential vitamins, which must be obtained from food, vi ta min D can be synthesized in the giao diện through a photosynthetic reaction triggered by exposure to UVB radiation. The efficiency of production depends on the number of UVB photons that penetrate the giao diện, a process that can be curtailed by clothing, excess body toàn thân fat, sunscreen, & the hình mẫu pigment melanin. For most trắng people, a half-hour in the summer sun in a bathing suit can initiate the release of 50,000 IU ( 1.25 mg ) vi ta min D into the circulation within 24 hours of exposure ; this same amount of exposure yields 20,000 – 30,000 IU in tanned individuals & 8,000 – 10,000 IU in dark-skinned people .The initial photosynthesis produces vi ta min D3, most of which undergoes additional transformations, starting with the production of 25 – hydroxyvitamin D ( 25 [ OH ] D ), the major size of vi ta min D circulating in the bloodstream và the size that is routinely measured to determine a person’s vi ta min D status. Although various cell types within the giao diện can carry out this transformation locally, the conversion takes place primarily in the liver. Another phối of transformations occurs in the kidney & other tissues, forming 1,25 ( OH ) D. This khung of the vi ta min is actually a hooc môn, chemically akin to the steroid hormones .1,25 ( OH ) D accumulates in cell nuclei of the intestine, where it enhances calcium & phosphorus absorption, controlling the flow of calcium into và out of bones to regulate bone-calcium metabolism. Michael Holick, a medical professor & director of the Bone Health Care Clinic at Boston University Medical Center, says, “ The primary physiologic function of vi ta min D is to maintain serum calcium & phosphorous levels within the normal physiologic range to tư vấn most metabolic functions, neuromuscular transmission, & bone mineralization. ”Without sufficient vi ta min D, bones will not size properly. In children, this causes rickets, a disease characterized by growth retardation & various skeletal deformities, including the hallmark bowed legs. More recently, there has been a growing appreciation for vi ta min D’s impact on bone health in adults. In August 2007, the Agency for Health Care Policy and Research published Effectiveness & Safety of Vitamin D in Relation to Bone Health, a systematic reviews of 167 studies that found “ fair evidence ” of an association between circulating 25 ( OH ) D concentrations và either increased bone-mineral mật độ trùng lặp từ khóa or reduced falls in older people ( a result of strengthened muscles as well as strengthened bones ). “ Low vi ta min D levels will precipitate và exacerbate osteoporosis in both men & women & cause the painful bone disease osteomalacia, ” says Holick .

Evolution of the Great Solar Debate

In the 2002 book Bone Loss và Osteoporosis in Past Populations : An Anthropological Perspective, Reinhold Vieth, a nutrition professor at the University of Toronto, writes that early primates probably acquired their relatively high vi ta min D requirements from frequent grooming và ingestion of oils rich in vi ta min D precursors that were secreted by their hình mẫu onto their fur. 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 hình mẫu to avoid photodegradation of micronutrients & protect sweat glands from UVR-induced injury .In the July 2.000 issue of the Journal of Human Evolution, California Academy of Sciences anthropologists Nina Jablonski & George Chaplin wrote that because dark hình mẫu requires about five to six times more solar exposure than pale giao diện for equivalent vi ta min D photosynthesis, và because the intensity of UVB radiation declines with increasing latitude, one could surmise that hình mẫu lightening was an evolutionary adaptation that allowed for optimal survival in low-UVR climes, assuming a traditional diet và outdoor lifestyle. Cooler temperatures in these higher latitudes resulted in the need for more clothing và shelter, further reducing UVR exposure. With shorter winter days và insufficient solar radiation in the UVB wavelengths needed to stimulate vi ta min D synthesis, dietary sources such as fatty fish became increasingly important .Over phút giây, clothing became the norm in higher latitudes và then eventually a mạng xã hội attribute in many societies. By the 1600 s, peoples in these regions covered their whole body toàn thân, even in summertime. Many children who lived in the crowded và polluted industrialized cities of northern Europe developed rickets. By the late 1800 s, approximately 90 % of all children living in industrialized Europe & 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 và the October 2007 American Journal of Public Health .Doctors throughout Europe và 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 & treatment .Around the giây phút 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 và 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 và good nutrition than to UVR. Nevertheless, a meta-analysis published in the February 2008 International Journal of Epidemiology found that high vi ta min 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 & TB spread, attitudes toward sun exposure underwent a radical shift. The suntan became valued in the Western world as a mới nhất status symbol that signified both health & wealth, as only the affluent could afford to vacation by the sea và play outdoor sports. Phototherapy quickly emerged as a popular medical treatment not only for TB, but also for rheumatic disorders, diabetes, gout, chronic ulcers, và wounds. The “ healthy rã ” was in, & “ sickly-looking ” pale giao diện was out .

Cancer: Cause, Protection, or Both?

The first reports of an association between sun exposure và hình mẫu cancer began to surface in dermatology publications in the late nineteenth century. Nevertheless, it was not until the 1930 s that the U.S. Public Health Service began issuing warnings about sun-related health risks. People were cautioned to avoid the midday summer sun, cover their heads in direct sunlight, & gradually increase the thời gian of sun exposure from an initial 5 – 10 minutes per day to minimize the risk of sunburn .In the decades that followed, the giao diện cancer hazards of excessive sun exposure would be extensively studied & mapped. Today, the three main forms of hình mẫu cancer — melanoma, basal cell carcinoma, & squamous cell carcinoma — are largely attributed to excessive UVR exposure. Skin cancers became the most common khung of cancer worldwide, especially among groups such as Trắng residents of Australia & New Zealand .When atmospheric scientists first called attention to possible chemical destruction of the stratospheric ozone layer in the early 1970 s, one predicted consequence of the increased UVB radiation was a rise in giao diện cancer rates, especially in nước Australia, New Zealand, South Africa, và Latin America. To counter this threat, the WHO, the United Nations Environment Programme, the World Meteorological Organization, the International Agency for Research on Cancer, & the International Commission on Non-Ionizing Radiation Protection established INTERSUN, the Global UV Project, with the express goal of reducing the burden of UVR-related disease. INTERSUN activities have included the development of an internationally recognized UV Index to help frame sun protection messages related to the daily intensity of UVR. [ For more information on these activities, see “ WHO Ultraviolet Radiation Website, ” p. A157 this issue. ]nước Australia was among the first countries to spearhead large-scale sun protection programs, with the Slip-Slop-Slap initiative ( short for “ slip on a shirt, slop on some sun-screen, và slap on a hat ” ) introduced in the early 1980 s. “ This program & the subsequent SunSmart chiến dịch have been highly effective in informing Australians of the risks và providing clear, practical instructions as to how to avoid excessive UVR exposure, ” says Lucas. As a result of increased use of hats, sunscreen, & shade, the incidence of malignant melanoma has begun to plateau in nước Australia, New Zealand, Canada, và Northern Europe among some age groups. However, because other UVR-induced giao diện cancers typically take longer than melanoma to develop, their incidence rates continue to rise in most developed countries. Lucas says a gradual improvement in these rates is to be expected as well .Whereas giao diện 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, và other cancers, as compared with living at lower latitudes. A randomized clinical trial by Joan Lappe, a medical professor at Creighton University, và colleagues, published in the June 2007 issue of the American Journal of Clinical Nutrition, confirmed that taking 2 – bốn times the daily dietary reference intake of 200 – 600 IU vi ta min D3 & calcium resulted in a 50 – 77 % reduction in expected incidence rates of all cancers combined end 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 toàn thân, và occupational exposure to sunlight actually reduced melanoma risk in a study reported in the June 2003 Journal of Investigative Dermatology .

Other Health Links

Various studies have linked low 25 ( OH ) D levels to diseases other than cancer, raising the possibility that vi ta min D insufficiency is contributing to many major illnesses. For example, there is substantial though not definitive evidence that high levels of vi ta min 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 & prevalence of MS ; a reviews in the December 2002 issue of Toxicology by epidemiology professor Anne-Louise Ponsonby & 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 % .Still to be resolved, however, is the question of what levels of vi ta min D are optimal for preventing the disease — và whether the statistical associations reflect different ren pools rather than different levels of 25 ( OH ) D. ( Interestingly, Holick reported in the August 1988 issue of The Journal of Clinical Endocrinology và Metabolism that no previtamin D3 formed when human hình mẫu was exposed to sunlight on cloudless days in Boston, at 42.2 ° N, from November through February or in Edmonton, at 52 ° N, from October through March. )“ Scientific evidence on specific effects of vi ta min D in preventing MS or slowing its progression is not sufficient, ” says Alberto Ascherio, a nutritional epidemiologist at the Harvard School of Public Health. “ Nevertheless, considering the safety of vi ta min D even in high doses, there is no clear contraindication, & because vi ta min D deficiency is very prevalent, especially among MS patients, taking vi ta min D supplements & getting moderate sun exposure is more likely to be beneficial than not. ”As with MS, there appears to be a latitudinal gradient for type một diabetes, with a higher incidence at higher latitudes. A Swedish epidemiologic study published in the December 2006 issue of Diabetologia found that sufficient vi ta min D status in early life was associated with a lower risk of developing type một diabetes. Nonobese mice of a strain predisposed to develop type một 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 vi ta min D per day from một year of age on had an 80 % decreased risk of developing type một diabetes later in life, whereas children who were vi ta min D deficient had a fourfold increased risk. Researchers are now seeking to understand how much UVR / vi ta min D is needed to lower the risk of diabetes & 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 và cardiovascular disease. A study in the September 2006 issue of Progress in Biophysics và Molecular Biology demonstrated that in young và elderly adults, serum 25 ( OH ) D was inversely correlated with blood glucose concentrations & insulin resistance. Some studies have demonstrated high prevalence of low vi ta min 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, và patients with cardiovascular disease are often found to be deficient in vi ta min D, according to research by Harvard Medical School professor Thomas J. Wang và 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 hooc môn renin in the kidneys, ” says Holick. “ Moreover, there is an inflammatory component to atherosclerosis, & vascular smooth muscle cells have a vi ta min D receptor & relax in the presence of 1,25 ( OH ) D, suggesting a multitude of mechanisms by which vi ta min D may be cardioprotective. ”To determine the potential links betwen sun exposure và the protective effect in preventing hypertension, Rolfdieter Krause of the Free University of Berlin Department of Natural Medicine và colleagues exposed a nhóm of hypertensive adults to a tanning bed that emitted full-spectrum UVR similar to summer sunlight. Another nhóm 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 và an average 6 milimet Hg decrease in their systolic và diastolic blood pressures, bringing them into the normal range. In constrast, the nhóm that used the UVA-only tanning bed showed no change in either 25 ( OH ) D or blood pressure. Thes e results were published in the 29 August 1998 issue of The Lancet. According to Krause, who currently heads the Heliotherapy Research Group at the Medical University of Berlin, a serum 25 ( OH ) D cấp độ of at least 40 ng / mL should be adequate to protect against hypertension và other forms of cardiovascular disease ( as well as cancers of the prostate và colon ) .William Grant, who directs the Sunlight, Nutrition, & Health Research Center, a research & education organization based in San Francisco, suspects that sun exposure và higher 25 ( OH ) D levels may confer protection against other illnesses such as rheumatoid arthritis ( RA ), asthma, và infectious diseases. “ Vitamin D induces cathelicidin, a polypeptide that effectively combats both bacterial & viral infections, ” Grant says. “ This mechanism explains much of the seasonality of such viral infections as influenza, bronchitis, và gastroenteritis, & bacterial infections such as tuberculosis & septicemia. ” For example, RA is more severe in winter, when 25 ( OH ) D levels tend to be lower, và is also more prevalent in the higher latitudes. In addition, 25 ( OH ) D levels are inversely associated with the clinical status of RA patients, & greater intake of vi ta min D has been linked with lower RA risk, as reported in January 2004 in Arthritis và Rheumatism .Some reports, including an article in the October – December 2007 issue of Acta Medica Indonesiana, indicate that sufficient 1,25 ( OH ) D inhibits induction of disease in RA, collagen-induced arthritis, Lyme arthritis, autoimmune encephalomyelitis, thyroiditis, inflammatory bowel disease, và systemic lupus erythematosus. Nonetheless, interventional dữ liệu are lacking for most autoimmune disorders & infectious diseases, with the exception of TB .

How Much Is Enough?

Gilchrest points out a problem with the literature : “ Everyone recommends something different, depending on the studies with which they are most aligned. One study reports an increased risk of prostate cancer for men with 25 ( OH ) D levels above 90 ng / mL, for example. ” In the June 2007 Lappe article, she notes, subjects in the control “ high-risk ” unsupplemented nhóm had 25 ( OH ) D levels of 71 nmol / L & the supplemented nhóm had levels of 96 nmol / L .Nevertheless, given the epidemiologic backdrop described above, there are now calls to rethink sun exposure policy or to promote vi ta min D supplementation in higher-risk populations. Such groups include pregnant or breastfeeding women ( these states draw upon a mother’s own reserves of vi ta min D ), the elderly, và those who must avoid the sun. Additionally, solely breastfed infants whose mothers were vi ta min D deficient during pregnancy have smaller reserves of the nutrient và are at greater risk of developing rickets. Even in the sun-rich environment of the Middle East, insufficient vi ta min D is a severe problem among breast-fed infants of women who wear a burqa ( a traditional garment that covers the body toàn thân from head to foot ), as reported in the February 2003 Journal of Pediatrics .Several recent reports indicate an increase in rickets particularly among breastfed đen infants, though White babies also are increasingly at risk. A study in the February 2007 Journal of Nutrition concluded that Black và Trắng pregnant women & neonates in the northern United States are at high risk of vi ta min D insufficiency, even when mothers take prenatal vitamins ( which typically provide 100 – 400 IU vi ta min D3 ). Studies by Bruce Hollis, director of pediatric nutritional sciences at the Medical University of South Carolina, & colleagues suggest that a maternal vi ta min D3 intake of 4,000 IU per day is safe và sufficient to ensure adequate vi ta min D status for both mother và nursing infant .Thes e days, most experts define vi ta min D deficiency as a serum 25 ( OH ) D cấp độ of less than đôi mươi ng / mL. Holick và others assert that levels of 29 ng / mL or lower can be considered to indicate a relative insufficiency of vi ta min D. Using this scale & considering various epidemiologic studies, an estimated một billion people worldwide have vi ta min D deficiency or insufficiency, says Holick, who adds, “ According to several studies, some forty to one hundred percent of the U.S. & European elderly men & women still living in the community [ that is, not in nursing homes ] are vi ta min D deficient. ” Holick asserts that a large number of infants, children, adolescents, & postmenopausal women also are vi ta min D insufficient. “ Thes e individuals have no apparent skeletal or calcium metabolism abnormalities but may be at much higher risk of developing various diseases, ” Holick says .In the context of inadequate sunlight or vi ta min D insufficiency, some scientists worry that the emphasis on preventing hình mẫu cancers tends to obscure the much larger mortality burden posed by more life-threatening cancers such as lung, colon, và breast cancers. Many studies have shown that cancer-related death rates decline as one moves toward the lower latitudes ( between 37 ° N & 37 ° S ), & 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 giao diện cancer, ” says Vieth. “ At the same thời gian, 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 vi ta min D, it does is not appear to be the best policy to advise people to simply keep out of the sun just to prevent giao diện cancer. ”To maximize protection against cancer, Grant recommends raising 25 ( OH ) D levels to between 40 và 60 ng / mL. Research such as that described in Holick’s August 2006 Journal of Clinical Investigation article indicates that simply keeping the serum màn chơi above đôi mươi 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 cấp độ of 55 – 60 ng / mL may reduce the breast cancer rate in temperate regions by half, và 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 & Europe, beyond not smoking. ” Moreover, these levels could be readily achieved by consuming no more than 2,000 IU / day of vi ta min D3 at a cost of less than USD trăng tròn per year và, unless there are contraindications to sunlight exposure, spending a few minutes outdoors ( 3 – 15 minutes for whites và 15 – 30 minutes for blacks ) when the sun is highest in the sky, with 40 % of the giao diện area exposed .Holick, Vieth, & many other experts now make a similar daily recommendation : 4,000 IU vi ta min D3 without sun exposure or 2,000 IU plus 12 – 15 minutes of midday sun. They say this màn chơi is quite safe except for sun-sensitive individuals or those taking medications that increase photosensitivity .Gilchrest says some sunlight enters the hình mẫu even through a high-SPF sunscreen, so sánh people can maximize their dermal vi ta min D production by spending additional phút giây outdoors while wearing protection. “ Without the sunscreen, this same individual would be incurring substantially more damage to her hình mẫu but not further increasing her vi ta min D level, ” she says .

Creating a Balanced Message

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, và that the risks can be minimized by carefully managing UVR exposure ( e. g., by avoiding sunburn ), as well as by increasing one’s intake of dietary antioxidants và limiting dietary fat và caloric intake. Antioxidants including polyphenols, apigenin, curcumin, proanthocyanidins, resveratrol, và silymarin have shown promise in laboratory studies in protecting against UVR-induced giao diện cancer, perhaps through antimutagenic or immune-modulating mechanisms .Central to the emerging debate is the issue of how to best construct public health messages that highlight the pros và cons of sun exposure in a balanced way. Such messages must necessarily take into trương mục variations in hình mẫu pigmentation between groups và these groups ’ differing susceptibilities to the dangers và benefits of sun exposure. Moreover, says Patricia Alpert, a nursing professor at the University of Las Vegas, age matters. “ The elderly [ have a ] declining capacity to make vi ta min D, ” she says. “ Many elderly, especially those living in nursing homes, are vi ta min D deficient, [ even ] those living in areas considered to have adequate sunshine. ”Many experts are now recommending a middle-ground approach that focuses on modest sun exposures. Gilchrest says the American Academy of Dermatology & most dermatologists currently suggest sun protection in combination with vi ta min D supplementation as a means of minimizing the risk of both hình mẫu cancer & internal cancers. Furthermore, brief, repeated exposures are more efficient at producing vi ta min D. “ Longer sun exposures cause further sun damage to giao diện và increase the risk of photo-aging và giao diện cancer, but bởi not increase vi ta min D production, ” she explains .Lucas adds that people should use sun protection when the UV Index is more than tam. As part of Australia’s SunSmart program, “ UV Alerts ” are announced in newspapers throughout the country whenever the index is forecast to be ba or higher. “ Perhaps, ” she says, “ this practice should be extended to other nations as well. ” U.S. residents can obtain UV Index forecasts through the EPA’s SunWise website ( http://epa.gov/sunwise/uvindex.html ) .In the near future, vi ta min D và health guidelines regarding sun exposure may need to be revised. But many factors not directly linked to sun protection will also need to be taken into tài khoản. “ Current observations of widespread vi ta min D insufficiency should not be attributed only to sun protection strategies, ” says Lucas. “ Over the same period there is a trend to an increasingly indoor lifestyle, associated with technological advances such as television, computers, & video clip games. ” She says sun-safe messages remain important — possibly more so sánh 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 .

Serotonin, Melatonin, and Daylight

As diurnal creatures, we humans are programmed to be outdoors while the sun is shining & trang chủ in bed at night. This is why melatonin is produced during the dark hours & stops upon optic exposure to daylight. This pineal hooc môn is a key pacesetter for many of the body’s circadian rhythms. It also plays an important role in countering infection, inflammation, cancer, và auto-immunity, according to a đánh giá in the May 2006 issue of Current Opinion in Investigational Drugs. Finally, melatonin suppresses UVR-induced giao diện damage, according to research in the July 2005 issue of Endocrine .When people are exposed to sunlight or very bright artificial light in the morning, their nocturnal melatonin production occurs sooner, và they enter into sleep more easily at night. Melatonin production also shows a seasonal variation relative to the availability of light, with the hooc môn 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, và 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 và short days, high serotonin levels in the presence of melatonin reflect short nights và long days ( i. e., longer UVR exposure ). Moderately high serotonin levels result in more positive moods và 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. It was recently found that mammalian giao diện can produce serotonin và transform it into melatonin, & that many types of hình mẫu cells express receptors for both serotonin & melatonin .With our modern-day penchant for indoor activity & 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, và moreover that we all try to sleep in total darkness. This can have a major impact on melatonin rhythms và can result in improvements in mood, energy, và sleep unique. ”For people in jobs in which sunlight exposure is limited, full-spectrum lighting may be helpful. Sunglasses may further limit the eyes ’ access to đầy đủ sunlight, thereby altering melatonin rhythms. Going shades-free in the daylight, even for just 10 – 15 minutes, could confer significant health benefits .

Other Sun-Dependent Pathways

The sun may be best known for boosting production of vi ta min D, but there are many other UVR-mediated effects independent of this pathway .

Direct immune suppression. 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.

Alpha melanocyte-stimulating hormone (α-MSH). Upon exposure to sunshine, melanocytes and keratinocytes in the skin release α-MSH, which has been implicated in immunologic tolerance and suppression of contact hypersensitivity. α-MSH also helps limit oxidative DNA damage resulting from UVR and increases gene repair, thus reducing melanoma risk, as reported 15 May 2005 in Cancer Research.

Calcitonin gene-related peptide (CGRP). 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.

Neuropeptide substance P. Along with CGRP, this neuropeptide is released from sensory nerve fibers in the skin following UVR exposure. This results in increased lymphocyte proliferation and chemotaxis (chemically mediated movement) but may also produce local immune suppression.

Endorphins. UVR increases blood levels of natural opiates called endorphins. Melanocytes in human skin express a fully functioning endorphin receptor system, according to the June 2003 Journal of Investigative Dermatology, and a study published 24 November 2005 in Molecular and Cellular Endocrinology suggests that the cutaneous pigmentary system is an important stress-response element of the skin.

Research Challenges

Growing evidence of the beneficial effects of UVR exposure has challenged the sun-protection paradigm that has prevailed for decades. Before a sun-exposure policy change occurs, however, we need to know if there is enough evidence to infer a protective effect of sun exposure against various diseases .Only through well-designed randomized clinical trials can cause-and-effect relationships be established. However, most sunlight-related epidemiologic research to date has relied on observational dữ liệu that are subject to considerable bias & confounding. Findings from observational studies are far less rigorous và reliable than those of interventional studies. But interventional studies would need to be very large và carried out end several decades ( since most UVR-mediated diseases occur later in life ). Moreover, it is not at all clear when, kết thúc a lifetime, sun exposure / vi ta min D is most important. So for now scientists must rely on the results of well-conducted observational analytic studies .In sunlight-related research, there are two main exposures of interest : vi ta min D status, which is measured by the serum 25 ( OH ) D màn chơi ; & personal UVR dose, which involves three fundamental factors : ambient UVR ( a function of latitude, altitude, atmospheric ozone levels, pollution, & giây phút of year ), amount of hình mẫu exposed ( a function of behavioral, cultural, & clothing practices ), & hình mẫu pigmentation ( with dark giao diện receiving a smaller effective dose to underlying structures than light hình mẫu ) .When measuring sun exposure at the individual màn chơi, many scientists have relied on latitude or ambient UVR of residence. But these measures are fraught with uncertainties. “ While ambient UVR varies ,. .. so sánh too bởi vì a variety of other possible etiological factors, including diet, exposure to infectious agents, temperature, và possibly even physical activity levels, ” says Robyn Lucas, an epidemiologist at Australia’s National Centre for Epidemiology & Population Health. “ Additionally, under any màn chơi of ambient UVR, the personal UV dose may vary greatly. In short, there is no real specificity for ambient UVR. ”Researchers also assess history of giây phút in the sun at various ages, history of sunburns, dietary và supplemental vi ta min D intake, & other proxy measures. Nonetheless, says Lucas, “ there are drawbacks to inferring that a relationship with any proxy for the exposure of interest is a relationship with personal UV dose or vi ta min D status. ” On the bright side, she adds, our ability to accurately gauge an individual’s UV dose history has been enhanced with the use of silicone rubber casts of the back of subjects ’ hands. The fine lines recorded by the cast provide an objective measure of cumulative sun damage .Open in a separate windowOpen in a separate windowOpen in a separate windowOpen in a separate windowOpen in a separate window

Articles from Environmental Health Perspectives are provided here courtesy of National Institute of Environmental Health Sciences

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