Long-time exposure to sunlight is associated with the risk of sudden cardiac arrest and coronary heart disease

Abstract

Abstract Background With ongoing climate change, the duration of sunshine hours will likely increase over the coming decades that escalating air temperature. Little is known about the potential cardiovascular risk from this climate factor. Purpose The aim of this study was to test whether duration of sunlight exposure is associated with incident sudden cardiac arrest (SCA), coronary heart disease (CHD), and hospitalization for heart failure (HF) and whether this association depends on seasonal variation. Methods A total of 308,851 participants from UK Biobank were included and were followed for a median time of 11.8 years. Participants reported how many hours they respectively spent the daylight outdoors on summer and winter typical days. Extreme outliers (>12 hours/day in summer and >8 hours/day in winter) were excluded. Average exposure time was calculated to unify the daylight outdoors time standard. Duration of sunlight exposure (average, summer, and winter) were categorized using quantiles and a restricted cubic spline for outcomes. Multivariate cox proportional hazard regression adjusted by age, sex, demographics, lifestyle, clinical and environmental factors was used for the analysis. Results During a follow-up, 1,572 (0.51%), 11,557 (3.74%) and 2,145 (0.68%) participants were diagnosed with SCA, CHD and hospitalization for HF. Compared with the participants exposed to short-time sunlight (average ≤ 1.5 hours/day), those who exposed to long-term sunlight (average ≥ 3.5 hours/day) had increased risk of SCA (HR 1.22, 95% CI 1.06 to 1.40) and CHD (HR 1.22, 95% CI 1.06 ~1.40). The associations between long-time exposure to sunlight and SCA were largely attributable to summer (HR 1.22, 95% CI 1.06 to 1.39) and not winter (HR 1.02, 95% CI 0.86 to 1.20), respectively. An hour increase of sunlight exposure was associated with increased risk of SCA in summer (HR, 1.03; 95% CI, 1.01 to 1.05), but not in winter (HR, 1.03, 95% CI, 0.99 to 1.06). Subgroup analysis identified that exposure to long-term sunlight was consistently increased risk of SCA, regardless of age, sex, body mass index, previous cardiovascular diseases, total physical activity, types of physical activity in last 4 weeks, use of sun/UV protection, sedentary time, natural environment percentage (buffer 1000m), and PM2.5. Finally, long-time exposure to sunlight was also associated with increased risk of CHD, but not associated with increased risk of HF hospitalization. Conclusions Findings from the present study indicate that daily long-time exposure to sunlight that increase in air temperature is a risk factor for SCA and CHD. These associations revealed graded relationship according to the duration of exposure to sunlight and more pronounced in summer. Our results suggest that public health efforts to reduce cardiovascular risk should take a wide range of exposure time to sunlight into account.