# Sun exposure and health Rating: Promising — Some human trials, or consistent animal work with a clear mechanism Type: Therapy Updated: 2026-10-18 Canonical: https://heretic.bio/articles/sun-exposure-and-health.html > Sun exposure has benefits beyond vitamin D. In a Swedish cohort of nearly 30,000 women followed for 20 years, sun avoiders had higher all-cause mortality, mainly from cardiovascular and other non-cancer deaths, with a gap comparable to smoking. UVA light releases nitric oxide from the skin and lowers blood pressure in small studies. The trade-off is skin cancer: melanoma risk is tied mainly to intermittent intense exposure and sunburn. The evidence is observational, so causality is not settled. Public-health advice on sunlight has focused almost entirely on one harm: skin cancer. That harm is real. But a body of cohort, mechanistic and light-sensor research suggests that regular, non-burning sun exposure has benefits that vitamin D pills do not reproduce, from lower blood pressure to lower all-cause mortality. This entry sets out both sides with the numbers, because sun advice that ignores either one is incomplete. For vitamin D specifically, see [Vitamin D optimization](vitamin-d-optimization.html). ## Sun avoidance and mortality: the Swedish cohort The Melanoma in Southern Sweden (MISS) cohort followed 29,518 women aged 25 to 64 for 20 years. Women who avoided the sun had about twice the all-cause mortality of those with the most active sun-exposure habits (PMID [24697969](https://pubmed.ncbi.nlm.nih.gov/24697969/)). A follow-up competing-risk analysis found: * The survival gap came mainly from fewer cardiovascular and other non-cancer deaths among sun-seekers. * Because sun-seekers lived longer, cancer made up a larger share of their deaths. * Non-smokers who avoided the sun had a life expectancy similar to smokers with the most sun exposure; avoiders lost 0.6 to 2.1 years of life expectancy (PMID [26992108](https://pubmed.ncbi.nlm.nih.gov/26992108/)). This is observational. Women who spend time in the sun may be healthier, more active or wealthier in ways a questionnaire cannot fully capture, and the cohort is Swedish women only, at a latitude where UV is weak much of the year. ## Mechanism: UVA, nitric oxide and blood pressure Skin stores nitric oxide (NO) compounds. In 24 healthy volunteers, UVA exposure lowered blood pressure and raised circulating nitrite, and forearm blood flow increased independently of the NO-producing enzymes, pointing to release of pre-formed NO stores in the upper skin. This effect has nothing to do with vitamin D, which is made by UVB (PMID [24445737](https://pubmed.ncbi.nlm.nih.gov/24445737/)). At population scale, in 342,457 US dialysis patients, higher local UV was associated with lower systolic blood pressure even after adjusting for temperature (PMID [32106744](https://pubmed.ncbi.nlm.nih.gov/32106744/)). ## Light timing: bright days, dark nights In 88,905 UK Biobank participants who wore light sensors for a week, brighter daytime light was linked to incrementally lower all-cause mortality over 8 years (adjusted HR as low as 0.66 to 0.83 in the brightest tenth), and brighter night-time light to higher mortality (HR up to 1.21 to 1.34), largely through cardiometabolic deaths (PMID [39405349](https://pubmed.ncbi.nlm.nih.gov/39405349/)). The study measured light, not UV or time outdoors, so it supports bright days and dark nights rather than sun exposure as such. See [Sleep optimization](sleep-optimization.html) for the circadian side. ## The melanoma trade-off The pattern of exposure matters. A meta-analysis of 57 studies found that **intermittent** intense exposure and a history of **sunburn** are clear risk factors for melanoma, whereas high, continuous occupational exposure was, if anything, inversely associated with it (PMID [15617990](https://pubmed.ncbi.nlm.nih.gov/15617990/)). In the Swedish cohort, sun-seekers' longer lives came with a larger share of cancer deaths (PMID [26992108](https://pubmed.ncbi.nlm.nih.gov/26992108/)). The trade-off is real and depends on skin type, latitude and burning: the evidence for benefit is about regular exposure that does not burn, and none of it supports tanning beds or sunburn. For people who have already had non-melanoma skin cancer, oral nicotinamide has phase 3 evidence for reducing new ones (see [Nicotinamide for skin cancer and glaucoma](nicotinamide-skin-cancer-and-glaucoma.html)). ## Where it sits on the Heretic scale **Promising.** Consistent observational associations with lower mortality and blood pressure, a plausible vitamin-D-independent mechanism shown in a controlled human study, and a large objective light-sensor cohort. No randomized trial of sun exposure on hard outcomes exists, and the skin-cancer cost is established. What would move it: trials of controlled UV or daylight exposure on blood pressure and cardiometabolic outcomes. Related: [Red light therapy](red-light-therapy.html), which uses the visible and near-infrared part of the spectrum without UV. ## Sources 1. Lindqvist PG, et al. (2014). "Avoidance of sun exposure is a risk factor for all-cause mortality: results from the Melanoma in Southern Sweden cohort." J Intern Med 276(1):77-86. PMID 24697969 . DOI 10.1111/joim.12251 (PubMed 24697969, DOI 10.1111/joim.12251) 2. Lindqvist PG, et al. (2016). "Avoidance of sun exposure as a risk factor for major causes of death: a competing risk analysis of the Melanoma in Southern Sweden cohort." J Intern Med 280(4):375-87. PMID 26992108 . DOI 10.1111/joim.12496 (PubMed 26992108, DOI 10.1111/joim.12496) 3. Liu D, et al. (2014). "UVA irradiation of human skin vasodilates arterial vasculature and lowers blood pressure independently of nitric oxide synthase." J Invest Dermatol 134(7):1839-1846. PMID 24445737 . DOI 10.1038/jid.2014.27 (PubMed 24445737, DOI 10.1038/jid.2014.27) 4. Weller RB, et al. (2020). "Does Incident Solar Ultraviolet Radiation Lower Blood Pressure?" J Am Heart Assoc 9(5):e013837. PMID 32106744 . DOI 10.1161/JAHA.119.013837 (PubMed 32106744, DOI 10.1161/JAHA.119.013837) 5. Windred DP, et al. (2024). "Brighter nights and darker days predict higher mortality risk: A prospective analysis of personal light exposure in >88,000 individuals." Proc Natl Acad Sci U S A 121(43):e2405924121. PMID 39405349 . DOI 10.1073/pnas.2405924121 (PubMed 39405349, DOI 10.1073/pnas.2405924121) 6. Gandini S, et al. (2005). "Meta-analysis of risk factors for cutaneous melanoma: II. Sun exposure." Eur J Cancer 41(1):45-60. PMID 15617990 . DOI 10.1016/j.ejca.2004.10.016 (PubMed 15617990, DOI 10.1016/j.ejca.2004.10.016)