The association between time spent outdoors during daylight and mortality among participants of the Adventist Health Study 2 Cohort

Abstract

Background: Prolonged exposure to sunlight increases the risk of skin cancer. However, multiple sunlight-related health benefits have been identified. The overall effect of sun exposure on mortality remains inconclusive. This study investigated the association between daylight exposure and mortality (all-cause and cause-specific: cancer, cardiovascular disease (CVD), and noncancer non-CVD mortalities). Methods: This study utilized the Adventist Health Study (AHS) 2 cohort of North America. Sun exposure was defined using time spent outdoors during daylight in warmer and cooler months. Mortality outcomes were identified through 2015. Multivariable Cox regression was used to examine the association between sun exposure and mortality. Results: This study included 83,205 AHS-2 participants enrolled between 2002 and 2007. We observed nonlinear (reverse J-shaped) associations between time outdoors in warmer months and the risks of all-cause, CVD, and noncancer non-CVD mortalities. Compared with spending 30 min/day during daylight in warmer months, spending 2 hours/day was associated with a lower risk of all-cause (hazard ratio: 0.90; 95% confidence interval = 0.86, 0.93), CVD (0.89; 0.83, 0.95), and noncancer non-CVD mortalities (0.83; 0.78, 0.89), but was not significantly associated with cancer mortality risk (1.02; 0.93, 1.13) after adjusting for physical activity and important confounders. All associations were weaker with the time spent outdoors in cooler months. Conclusions: Moderate time outdoors in daylight during warmer months could be associated with lower risks of all-cause, CVD, and noncancer non-CVD mortality; however, there was no clear evidence of an association with cancer mortality. Epidemiological studies need to investigate the balance between sun exposure's health benefits and risks.