How Does Sunlight Exposure Affect Health and Longevity?

The short answer

Sunlight exposure has both benefits and risks. A large Swedish cohort study found that avoiding sun exposure was associated with a mortality risk comparable to smoking. Sunlight triggers nitric oxide release from skin, lowering blood pressure, and stimulates vitamin D synthesis. However, excessive UV exposure is the primary cause of skin cancer. The optimal approach is regular moderate exposure while avoiding sunburn.

What the evidence actually shows

Lindqvist et al. (2016) in the Journal of Internal Medicine followed 29,518 Swedish women for 20 years and found that those who avoided sun exposure had a mortality rate 2-fold higher than those with the highest sun exposure, after controlling for confounders. The excess mortality was primarily from cardiovascular disease and non-cancer, non-cardiovascular causes. Liu et al. (2014) demonstrated that UV exposure triggers the release of nitric oxide from skin stores, causing systemic vasodilation and blood pressure reduction — a mechanism independent of vitamin D. Holick (2007) established that vitamin D deficiency is extremely common in populations with limited sun exposure and is associated with multiple adverse health outcomes.

"Avoiding sun exposure was associated with a mortality risk comparable to smoking, primarily from cardiovascular causes."

— Lindqvist et al., Journal of Internal Medicine 2016

What the major health authorities say

MedlinePlus and the NIH recommend vitamin D supplementation for individuals with limited sun exposure, particularly older adults, people with dark skin, and those living at high latitudes. The NIA recommends protecting skin from excessive sun exposure while acknowledging the importance of vitamin D. The American Academy of Dermatology recommends daily sunscreen use and avoiding peak UV hours (10am–4pm) to reduce skin cancer risk.

Practical implications

The optimal sun exposure strategy is: 10–30 minutes of midday sun exposure to arms and legs (without sunscreen) on most days during summer months in temperate climates — sufficient for vitamin D synthesis without significant skin damage risk; avoiding sunburn at all times (sunburn is the primary driver of skin cancer risk); using sunscreen on the face (which ages rapidly with UV exposure) while allowing body sun exposure for vitamin D; and supplementing with vitamin D3 (800–1,000 IU/day) during winter months in northern latitudes.

Where reasonable people still disagree

• Whether the cardiovascular benefits of sun exposure are primarily mediated by vitamin D or by nitric oxide release — the distinction matters for whether supplementation can substitute for sun exposure.
• The optimal amount of sun exposure for different skin types, latitudes, and seasons — recommendations vary significantly by these factors.
• Whether the skin cancer risk of moderate regular sun exposure is outweighed by the cardiovascular and other health benefits.