Does long-term exposure to outdoor artificial light at night have an impact on glucose homeostasis and the prevalence of diabetes? To decode this question, researchers from China enrolled 98,658 participants from the China Noncommunicable Disease Surveillance Study from 162 sites across mainland China in 2010. Their mean age was 42.7 years. Women comprised almost half (49.2%) of the study population. Exposure to outdoor light at night for a minimum duration of 6 months was determined with the help of satellite data. Exposure levels were categorized into five quintiles. People residing in areas of higher quintiles of outdoor light were older, had higher BMI and household income and lived in an urban area.

Analysis of data revealed a positive association between chronic exposure to outdoor light at night and glucose levels both fasting and postprandial, glycosylated hemoglobin (A1c) and insulin resistance measured via HOMA-IR (Homeostatic Model Assessment for Insulin Resistance) even after adjusting for many important diabetes risk factors. However, artificial light had a negative correlation with beta cell function as quantified by HOMA-B. Diabetes prevalence was significantly associated with per-quintile LAN exposure (PR 1.07). With every quintile exposure to artificial light at night, the risk in prevalence of diabetes increased by 7% with a prevalence ratio of 1.07. Diabetes prevalence was increased by 28% among participants exposed to the highest level of exposure to nighttime light (median 69.1 nW cm-2 sr-1) compared to those exposed the least (median 1.0 nW cm-2 sr-1) with an adjusted prevalence ratio of 1.28.

Rapid urbanization and industrialization has increased artificial lights at night. Excessive use of night outdoor artificial light causes what has been called light pollution. While the glittering lights are mesmerizing, they negatively affect health as demonstrated in this study. It shows that frequent exposure to the bright outdoor lights at night is associated with greater risk of hyperglycemia, insulin resistance and diabetes and suggests artificial light at night as a potential novel risk factor for diabetes. Disruption in the circadian rhythm has been hypothesized as the underlying mechanism. However, the study has shown only an association between the two and does not prove a causal relationship.

Reference

1. Zheng R, et al. Outdoor light at night in relation to glucose homoeostasis and diabetes in Chinese adults: a national and cross-sectional study of 98,658 participants from 162 study sites. Diabetologia. 2022 Nov 14. doi: 10.1007/s00125-022-05819-x.