Time spent in outdoor light is associated with increased blood pressure, higher hypertension risk, and lower hypotension risk

ObjectiveLight exposure is considered to be associated with reduced blood pressure (BP). However, longitudinal epidemiological studies concerning the light-BP association with large samples are still limited. MethodsThis cohort study enrolled over 300,000 participants from the UK Biobank. Information on time spent in outdoor light during typical summer or winter days was obtained through questionnaires. Cases of hypertension and hypotension were identified using the 10th edition of International Classification of Diseases codes. Cox proportional hazard regression models were employed to estimate the light-BP associations, restricted cubic splines were utilized to detect potential nonlinear associations, subgroup analyses were conducted to identify effect modifiers, and causal mediation analyses were performed to explore potential mechanisms. ResultsUsing summer light exposure as an illustration, after a median follow-up of 13.4 years, each additional hour of summer light exposure was associated with an increased risk of hypertension (hazard ratio [HR] 1.011, 95% confidence interval [CI] 1.006-1.017, P-nonlinear=0.803) and a decreased risk of hypotension (0.988, 0.977- 0.998, P-nonlinear=0.109). The light-BP association is stronger in females (P=0.022), those with short sleep duration (P=0.049), and those with high genetic risk of hypertension (P<0.001). Potential mechanisms included increasing biological age (proportion mediated, 24.1%, P<0.001), neutrophil count (5.4%, P<0.001), BMI (32.0%, P<0.001), etc. ConclusionsContrary to previous findings, our study revealed a positive association between light exposure and BP. Potential mechanisms include inflammation, aging, and behavioral lifestyle changes. Further epidemiological and experimental investigations are warranted to validate these novel findings.