Outdoor light at night exposure and hypertension risk in adults: A longitudinal cohort study from the FLORA project

Hypertension affects 27.5% of Chinese adults, yet remains poorly controlled. Light at Night (LAN) is an emerging environmental factor potentially linked to hypertension, but evidence from developing countries is limited.

This retrospective cohort study included 8308 hypertension-free adults from the Future Longitudinal Observational Research in Adults (FLORA) project (2012 baseline). Outdoor LAN exposure was assessed annually using VIIRS-DNB satellite data at 500m × 500m range based on each participant's residential address, with time-varying exposure levels updated according to follow-up residence changes. Participants underwent annual physical examinations over 9.22 years (mean follow-up). Time-varying Cox proportional hazards regression models were used to assess the association between outdoor LAN exposure and the risk of incident hypertension and hypertension subtype. Subgroup analyses were conducted to identify vulnerable populations. Bootstrap models (1000 resamplings) were performed to explore the extent to which body mass index (BMI), fasting blood glucose (FBG) and triglycerides (TG) could account for the LAN-hypertension association.

Compared with the lowest LAN quintile (Q1), participants in Q2-Q5 had significantly increased hypertension and hypertension subtype. For hypertension, the hazard ratios (HRs) from Q2 to Q5 were 1.14 (95%CI: 1.01, 1.29), 1.16 (95%CI: 1.03, 1.35), 1.19 (95%CI: 1.05, 1.35), and 1.23 (95%CI: 1.09, 1.40), respectively. BMI, FBG, and TG partially explained the association between outdoor LAN exposure and hypertension in exploratory analyses, accounting for 10.32% (95%CI: 6.69%, 16.09%), 4.81% (95%CI: 2.15%, 7.80%), and 1.71% (95%CI: 0.57%, 2.97%) of the total effect, respectively.

This cohort study provides longitudinal evidence that higher residential ambient light at night exposure is associated with an increased risk of hypertension in adults from a developing country. Abnormal metabolism represented by high BMI, FBG, and TG levels may partially serve as a potential explanation that needs further research.