Sunlight
Trials of sunlight and UV exposure raised blood vitamin D, though less than supplements in one trial. Pooled trials found more outdoor time cut new myopia in children. Daylight is linked to better mood and sleep in one large cohort. Sunburn is very common, and sunburn and sun exposure are linked to melanoma and other skin cancers.
Checked 2026-11-13
- Status
- A daily life factor, not a product.
- Also called
- sun exposure, sunshine, daylight, time outdoors, outdoor light, UV exposure, ultraviolet light, getting sun, morning sunlight, sunbathing
- Studied for
- vitamin D, mood, depression, sleep, body clock, energy, preventing myopia in children, blood pressure, living longer, bone health
Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on
Shown to help6
- StrongShown to cut new myopia in children by about 16% to 46% with more time outdoors, in three meta-analyses including several school trials.
- ModerateShown to raise blood vitamin D in trials of UV and sunlight exposure. Advised sunlight raised it less than vitamin D supplements in one trial.
- LimitedOne large cohort linked each extra daily hour outdoors in daylight to lower odds of depression and low mood, mostly in cross-sectional analyses.
- LimitedLimited evidence: daylight was linked to fewer insomnia symptoms in one cohort, and a week camping in natural light shifted the body clock earlier in a small study.
- LimitedOne small study found UVA light on the skin lowered blood pressure in 24 healthy volunteers, with signs of nitric oxide released from the skin.
- LimitedOne cohort of Swedish women linked active sun habits to fewer deaths from heart disease and other non-cancer causes, and 0.6 to 2.1 years longer life.
Reported risks3
- LimitedOne national survey found 34.2% of US adults had a sunburn in a year, and 51.2% of those aged 18 to 29.Very common
- StrongLinked to more melanoma with more sunburns and with intermittent sun exposure in three meta-analyses. Heavy continuous outdoor work showed an inverse link.How often is not known
- StrongLinked to more squamous and basal cell skin cancer in outdoor workers, about 77% and 43% higher odds, in two meta-analyses.How often is not known
What it was studied for, and what was found
Shown to help6
Vitamin D levels
Shown to raise blood vitamin D in trials of UV and sunlight exposure. Advised sunlight raised it less than vitamin D supplements in one trial.
Compared with before the exposures, in the same people [1]; different UVB doses and skin areas [2]; vitamin D3 800 IU daily or 100,000 IU every 3 months [3]; care homes with no added sunlight [4]
The numbers and sources
- Effect
- After simulated summer sunlight three times a week for 6 weeks in winter, 90% of adults reached a 25-hydroxyvitamin D level of 20 ng/mL and 26.2% reached 32 ng/mL [1]. The rise in 25-hydroxyvitamin D grew with UVB dose and, at small doses, with the area of skin exposed, and was smaller when the starting level was higher [2]. In vitamin D-deficient immigrants, advice to get sunlight raised 25-hydroxyvitamin D from 22.5 to 29.1 nmol/L over 6 months, against 53 nmol/L with 800 IU a day. Parathyroid hormone fell in all groups after 3 months, less with sunlight [3]. In frail older people, extra morning sunlight raised 25-hydroxyvitamin D only slightly, with a median adherence of 26% [4].
- Population
- 120 white adults aged 20 to 60 in Manchester, UK [1]. 92 participants [2]. 211 non-western immigrants aged 18 to 65 with a level under 25 nmol/L in the Netherlands [3]. 602 care home residents aged 70 and older, mean 86.4, in Sydney [4].
- Sources
- [1], [2], [3], [4]
- Caveats
- Two trials used UV lamps, not the sun [1][2]. Advice to go outdoors depends on whether people follow it [3][4]. Skin color, latitude, season and clothing change how much vitamin D the same time in the sun makes.
Myopia in children
Shown to cut new myopia in children by about 16% to 46% with more time outdoors, in three meta-analyses including several school trials.
Compared with control groups in trials and children spending less time outdoors in cohorts [5]; control groups in trials [6][7]; children in control schools who kept their usual activity [8]; children in control schools [9]
The numbers and sources
- Effect
- Outdoor time cut incident myopia in trials (RR 0.536, 95% CI 0.338 to 0.850) and cohorts (RR 0.574), and reduced myopic shift by 0.30 diopters over 3 years. In children already myopic, time outdoors was not related to progression [5]. Across 5 randomized trials, new myopia fell (RR 0.76, 95% CI 0.67 to 0.87), with no heterogeneity [6]. Across 7 randomized trials, myopia incidence fell (RR 0.84, 95% CI 0.78 to 0.91) and axial length grew 0.09 mm less [7]. An added 40-minute outdoor class each school day cut 3-year myopia incidence from 39.5% to 30.4% [8]. A recess-outdoors program slowed myopic shift in both myopic and non-myopic children over 1 year [9].
- Population
- 25 studies, 23 in children [5]. 3,014 children aged 6 to 12 in 5 trials, 9 to 36 months [6]. 9,437 children and adolescents in 7 trials [7]. 1,903 children aged about 6.6 in Guangzhou, China [8]. 693 first-graders in Taiwan [9].
- Sources
- [5], [6], [7], [8], [9]
- Caveats
- Most trials were in East Asia, where myopia is common. Outdoor time is daylight plus distance viewing, so sunlight is not the only possible cause. One trial found an effect at light levels as low as shade under trees [9]. The reviews disagree on children already myopic [5][9].
Mood
One large cohort linked each extra daily hour outdoors in daylight to lower odds of depression and low mood, mostly in cross-sectional analyses.
Compared with each hour less of daylight outdoors a day [10]
The numbers and sources
- Effect
- Participants spent a median 2.5 daylight hours outdoors a day. Each extra hour was linked to lower odds of lifetime major depression (95% CI for the odds ratio 0.92 to 0.98), antidepressant use (0.92 to 0.98) and low mood (0.87 to 0.90), and higher odds of happiness (1.41 to 1.48). Longitudinal analyses agreed with smaller effects [10].
- Population
- UK Biobank adults aged 37 to 73, 54% women, over 400,000 analyzed [10].
- Sources
- [10]
- Caveats
- Observational, with self-reported time outdoors. People who are depressed go out less, so reverse causation is likely in part, and outdoor time also brings exercise and company.
Sleep and body clock
Limited evidence: daylight was linked to fewer insomnia symptoms in one cohort, and a week camping in natural light shifted the body clock earlier in a small study.
Compared with each hour less of daylight outdoors a day [10]; the same people living with electric lighting [11]
The numbers and sources
- Effect
- Each extra daily hour outdoors was linked to fewer insomnia symptoms (95% CI for the odds ratio 0.94 to 0.97), less frequent tiredness (0.80 to 0.82), easier getting up (1.46 to 1.49) and an earlier chronotype [10]. After a week of natural light only, the internal biological night began at sunset and ended just after sunrise. Later chronotypes shifted the most [11].
- Population
- Over 400,000 UK Biobank adults [10]. 8 adults aged about 30, one week at home then one week camping in Colorado in July [11].
- Sources
- [10], [11]
- Caveats
- The cohort is observational [10]. The camping study was small and short, and measured clock timing, not sleep quality [11].
Blood pressure
One small study found UVA light on the skin lowered blood pressure in 24 healthy volunteers, with signs of nitric oxide released from the skin.
Compared with a control condition the source abstract does not describe [12]
The numbers and sources
- Effect
- Two standard erythemal doses of UVA on the skin lowered blood pressure, with falls in circulating nitrate and rises in nitrite. Forearm blood flow rose, independently of nitric oxide synthase [12].
- Population
- 24 healthy volunteers [12].
- Sources
- [12]
- Caveats
- A UV lamp in a laboratory, not sunlight. The abstract gives no size for the fall, and the effect was measured over hours, not weeks.
Death from any cause
One cohort of Swedish women linked active sun habits to fewer deaths from heart disease and other non-cancer causes, and 0.6 to 2.1 years longer life.
Compared with women who avoided sun exposure [13]
The numbers and sources
- Effect
- Women with active sun exposure habits had lower risk of cardiovascular and non-cancer, non-cardiovascular death than women who avoided the sun. Life expectancy of avoiders was 0.6 to 2.1 years shorter than in the highest sun exposure group. Because they lived longer, cancer made up a larger share of deaths among sun-seeking women [13].
- Population
- 29,518 Swedish women aged 25 to 64 at the start, followed 20 years [13].
- Sources
- [13]
- Caveats
- One observational cohort. Women who seek the sun may be healthier, more active and better off, and ill women may avoid going out, which is reverse causation.
Amounts studied
Laboratory trials used simulated summer sunlight of 1.3 standard erythemal doses three times a week for 6 weeks on people in T-shirts and shorts, which the authors equate to about 13 minutes of UK midday summer sun on 35% of the skin [1], and four UVB doses of 0.75 to 3.0 standard erythemal doses on 6% to 24% of the skin [2]. Field trials advised sunlight from March to September [3] or added 30 to 40 minutes a day of early morning sun for a year [4].
Myopia trials added a 40-minute outdoor class each school day for 3 years [8] or encouraged up to 11 hours a week outdoors at school [9], and lasted 9 to 36 months [6]. In the UK Biobank, adults reported a median 2.5 daylight hours outdoors a day [10]. The blood pressure study used two standard erythemal doses of UVA [12].
Risks
Reported risks3
Sunburn
One national survey found 34.2% of US adults had a sunburn in a year, and 51.2% of those aged 18 to 29.
The numbers and sources
- How common
- Very common: more than 1 in 10 people.
- Effect
- In 2015, 34.2% of US adults reported sunburn in the past year. Rates were 51.2% in adults aged 18 to 29, 42.5% in non-Hispanic white adults, 50.2% in people with sun-sensitive skin, 29.7% in Hispanic adults and 13.2% in Black adults. People who sought shade or stayed out of the sun had less sunburn [14].
- Population
- 31,162 US adults in a nationally representative household survey [14].
- Sources
- [14]
- Caveats
- Self-reported sunburn in a single year. It counts any sunburn, not its severity.
Melanoma
Linked to more melanoma with more sunburns and with intermittent sun exposure in three meta-analyses. Heavy continuous outdoor work showed an inverse link.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Melanoma risk rose with the number of sunburns in childhood, adolescence and adulthood, not only in childhood, and was highest per five sunburns a decade for adult and lifetime sunburns [15]. In fair-skinned people, a history of sunburn raised the odds of melanoma (adjusted OR 1.23, 95% CI 1.04 to 1.46, unadjusted 1.66), and cumulative sun exposure was linked in most studies [16]. Intermittent sun exposure and sunburn history were risk factors, while high occupational sun exposure was inversely associated with melanoma [17].
- Population
- 51 study populations [15]. 26 studies with 3,417 melanomas in the sunburn analysis, skin types I to IV [16]. 57 studies [17].
- Sources
- [15], [16], [17]
- Caveats
- Mostly case-control studies, with sunburn recalled after diagnosis. Risk depends heavily on skin type, which the reviews could not always adjust for [17].
Squamous and basal cell skin cancer
Linked to more squamous and basal cell skin cancer in outdoor workers, about 77% and 43% higher odds, in two meta-analyses.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Outdoor work with UV exposure was linked to squamous cell carcinoma (OR 1.77, 95% CI 1.40 to 2.22), similar in cohort and case-control studies, with stronger links at lower latitudes [18]. Outdoor work was linked to basal cell carcinoma (OR 1.43, 95% CI 1.23 to 1.66), also stronger at lower latitudes [19].
- Population
- 18 studies, 6 cohorts and 12 case-control [18]. 24 studies, 5 cohorts and 19 case-control [19].
- Sources
- [18], [19]
- Caveats
- The exposure is years of outdoor work, not everyday time in the sun. Outdoor workers were compared with people without occupational UV exposure.
Claims tested and not found
- That more sunlight cuts falls in frail older people. A year of extra morning sun did not change falls (IRR 1.06, 95% CI 0.76 to 1.48), with low adherence [4].
- That advice to get sunlight raises vitamin D as much as a supplement. After 6 months, advised sunlight brought 25-hydroxyvitamin D to 29.1 nmol/L, against 53 nmol/L with 800 IU a day [3].
Related
Sources
- Rhodes LE, Webb AR, Fraser HI, et al. Recommended summer sunlight exposure levels can produce sufficient (≥20 ng ml(-1)) but not the proposed optimal (≥32 ng ml(-1)) 25(OH)D levels at UK latitudes. Journal of Investigative Dermatology. 2010. https://doi.org/10.1038/jid.2009.417
- Bogh MK, Schmedes AV, Philipsen PA, et al. Interdependence between body surface area and ultraviolet B dose in vitamin D production: a randomized controlled trial. British Journal of Dermatology. 2011. https://doi.org/10.1111/j.1365-2133.2010.10082.x
- Wicherts IS, Boeke AJ, van der Meer IM, et al. Sunlight exposure or vitamin D supplementation for vitamin D-deficient non-western immigrants: a randomized clinical trial. Osteoporosis International. 2011. https://doi.org/10.1007/s00198-010-1343-x
- Sambrook PN, Cameron ID, Chen JS, et al. Does increased sunlight exposure work as a strategy to improve vitamin D status in the elderly: a cluster randomised controlled trial. Osteoporosis International. 2012. https://doi.org/10.1007/s00198-011-1590-5
- Xiong S, Sankaridurg P, Naduvilath T, et al. Time spent in outdoor activities in relation to myopia prevention and control: a meta-analysis and systematic review. Acta Ophthalmologica. 2017. https://doi.org/10.1111/aos.13403
- Cao K, Wan Y, Yusufu M, Wang N. Significance of Outdoor Time for Myopia Prevention: A Systematic Review and Meta-Analysis Based on Randomized Controlled Trials. Ophthalmic Research. 2020. https://doi.org/10.1159/000501937
- Mei Z, Zhang Y, Jiang W, et al. Efficacy of outdoor interventions for myopia in children and adolescents: a systematic review and meta-analysis of randomized controlled trials. Frontiers in Public Health. 2024. https://doi.org/10.3389/fpubh.2024.1452567
- He M, Xiang F, Zeng Y, et al. Effect of Time Spent Outdoors at School on the Development of Myopia Among Children in China: A Randomized Clinical Trial. JAMA. 2015. https://doi.org/10.1001/jama.2015.10803
- Wu PC, Chen CT, Lin KK, et al. Myopia Prevention and Outdoor Light Intensity in a School-Based Cluster Randomized Trial. Ophthalmology. 2018. https://doi.org/10.1016/j.ophtha.2017.12.011
- Burns AC, Saxena R, Vetter C, et al. Time spent in outdoor light is associated with mood, sleep, and circadian rhythm-related outcomes: A cross-sectional and longitudinal study in over 400,000 UK Biobank participants. Journal of Affective Disorders. 2021. https://doi.org/10.1016/j.jad.2021.08.056
- Wright KP, McHill AW, Birks BR, et al. Entrainment of the human circadian clock to the natural light-dark cycle. Current Biology. 2013. https://doi.org/10.1016/j.cub.2013.06.039
- Liu D, Fernandez BO, Hamilton A, et al. UVA irradiation of human skin vasodilates arterial vasculature and lowers blood pressure independently of nitric oxide synthase. Journal of Investigative Dermatology. 2014. https://doi.org/10.1038/jid.2014.27
- Lindqvist PG, Epstein E, Nielsen K, et al. Avoidance of sun exposure as a risk factor for major causes of death: a competing risk analysis of the Melanoma in Southern Sweden cohort. Journal of Internal Medicine. 2016. https://doi.org/10.1111/joim.12496
- Holman DM, Ding H, Guy GP, et al. Prevalence of Sun Protection Use and Sunburn and Association of Demographic and Behaviorial Characteristics With Sunburn Among US Adults. JAMA Dermatology. 2018. https://doi.org/10.1001/jamadermatol.2018.0028
- Dennis LK, Vanbeek MJ, Beane Freeman LE, et al. Sunburns and risk of cutaneous melanoma: does age matter? A comprehensive meta-analysis. Annals of Epidemiology. 2008. https://doi.org/10.1016/j.annepidem.2008.04.006
- Kwa M, Ravi M, Elhage K, et al. The risk of ultraviolet exposure for melanoma in Fitzpatrick skin types I-IV: A 20-year systematic review with meta-analysis for sunburns. Journal of the European Academy of Dermatology and Venereology. 2025. https://doi.org/10.1111/jdv.20316
- Gandini S, Sera F, Cattaruzza MS, et al. Meta-analysis of risk factors for cutaneous melanoma: II. Sun exposure. European Journal of Cancer. 2005. https://doi.org/10.1016/j.ejca.2004.10.016
- Schmitt J, Seidler A, Diepgen TL, Bauer A. Occupational ultraviolet light exposure increases the risk for the development of cutaneous squamous cell carcinoma: a systematic review and meta-analysis. British Journal of Dermatology. 2011. https://doi.org/10.1111/j.1365-2133.2010.10118.x
- Bauer A, Diepgen TL, Schmitt J. Is occupational solar ultraviolet irradiation a relevant risk factor for basal cell carcinoma? A systematic review and meta-analysis of the epidemiological literature. British Journal of Dermatology. 2011. https://doi.org/10.1111/j.1365-2133.2011.10425.x