Outdoor light at night and mortality in the UK Biobank: a prospective cohort study.

BACKGROUND: More than 83% of the world's population lives under light-polluted skies while information about health effects of outdoor light at night (LAN) is limited. We examined the association of LAN with natural cause (NC) and cardiovascular disease (CVD) mortality using the UK Biobank.

METHODS: We included 273 335 participants recruited between 2006 and 2010. Level of LAN was estimated at each participant's address using time-varying satellite data for a composite of persistent night-time illumination at ~1 km2 scale. Information on causes of death until 12 November 2021 was obtained through record linkage. Cox proportional hazards regression was used.

RESULTS: In the follow-up with an average of 12.4 years, 14 864 NC and 3100 CVD deaths were identified. Compared with the participants exposed to the first quartile of LAN, participants exposed to the highest quartile showed an 8% higher risk of NC mortality (HR: 1.08, 95% CI 1.03 to 1.13) after adjusting for age, sex, social-economic status, shift work, lifestyle factors and body mass index. However, the association disappeared after further adjustment for PM2.5 and evening noise, with HRs (95% CIs) of 1.02 (0.97 to 1.07), 1.01 (0.97 to 1.06) and 1.03 (0.97 to 1.08), respectively, for the participants exposed to the second, third and fourth quartiles of LAN. No significant associations were observed between LAN and CVD mortality, either.

CONCLUSIONS: We did not observe significant associations of LAN with NC and CVD mortality in this large nationwide cohort. The health effects of LAN remain unclear. Further studies are warranted to address this public health concern.