Time spent outdoors and risk of myocardial infarction and stroke in middle and old aged adults: Results from the UK Biobank prospective cohort

Time spent outdoors has been previously related to several cardiovascular risk factors, implying that it may confer either beneficial or harmful effects on cardiovascular health. However, no large population-based studies have examined the relation between time spent outdoors and myocardial infarction and stroke.We aimed to investigate the longitudinal relation between time spent outdoors and myocardial infarction and stroke in large UK population-based cohort.A total of 446,648 participants from UK Biobank were included in the study of which 431,146 participants (56% females and 44% males with a mean age of 56.4 ± 8.1 years) were followed for a median time of 7 years. Time spent outdoors was self-reported and participants were stratified into quantiles (less than 1.5 [reference group]; 1.5 to 2.4; 2.5 to 3.5 and more than 3.5 h per day outdoors). Myocardial infarction and stroke events were either collected from hospital records and death registries or were self-reported by the participants. Cox proportional hazard regression was used for the analysis. In addition to age and sex, analyses were adjusted for potential demographic (TDI, ethnic background, current employment status), lifestyle (alcohol intake frequency, current tobacco use, sedentary time and moderate-to-vigorous physical activity), health related factors (BMI, systolic and diastolic blood pressure) and environmental indicators (NO2, NOx, PM10, PM2.5-10, PM2,5, noise pollution, % greenspace, % natural environment and % water).A 20% increased risk for myocardial infarction incidence was observed among participants who reported spending more than 3.5 h/day outdoors (HR: 1.20, 95% CI: 1.06-1.36) compared to the reference group. A trend was also observed for stroke (HR: 1.14, 95% CI: 0.97-1.34).Findings from the present study indicate that spending more than 3.5 h/day outdoors is a risk factor for myocardial infarction and stroke. Future research is needed to further understand the relation between time spent outdoors and cardiovascular disease.