Outdoor Light Spending Time, Genetic Predisposition and Incident Parkinson's Disease： The mediating effect of lifestyle and vitamin D

Background Cross-sectional evidence implicates sunlight exposure is associated with the risk of Parkinson's disease (PD), whereas the evidence from prospective studies is scarce. Methods A cohort study based on UK Biobank enrolled participants between 2006 and 2010, with the latest follow-up in November 2022. In the prospective population-based study 375,599 UK adults aged 37–73 years were enrolled. The outdoor light time was assessed using a questionnaire survey to investigate how many hours were spent outdoors on typical summer and winter days. New-onset PD was identified through linkage with inpatient hospitalization and death registers. Multivariate Cox proportional hazard regression models were used. The polygenic risk score (PRS) for PD comprised 44 single-nucleotide variants. Results A total of 375,599 participants (mean age, 56.8 years; 46.3% males) were included, and 2,824 individuals were first-ever diagnosed with PD. Compared with the individuals with shorter outdoor light time, those with longer time in summer (HR 0.77; 95% CI, 0.68–0.88), in winter (HR 0.85; 95% CI, 0.75–0.96), and on average (HR 0.83; 95% CI, 0.74–0.93), were prone to have lower PD risk. There is no interaction between outdoor light time and genetic predisposition in PD. In mediation analyses, physical activities explained 13.24%, 25.72%, and 15.55% of the associations between outdoor light time and PD, respectively. Conclusion In this cohort study, a longer duration of outdoor light exposure was associated with a lower risk of PD, and independent of genetic risk of PD. This association is partly mediated by physical activity, vitamin D, and sleep patterns.