Light at night (LAN) is a significant but underappreciated risk factor contributing to cardiometabolic disease (CMD). We therefore conducted the review examining the relationship of LAN exposure with CMD in order to investigate the effects of LAN exposure on CMD. We searched PubMed, Web of Science, Embase, and Scopus for eligible studies published from database inception to August 17, 2023. The pooled effect size was calculated using random-effects models. Heterogeneity among the studies was quantified by Cochran's Q test and Istatistic. A total of 1,019,739 participants from 14 studies (5 cohort studies and 9 cross-sectional) were included. Among the 14 eligible studies, 9 on obesity, 4 on diabetes, 2 on hypertension, 1 on dyslipidemia, and 1 on coronary heart disease. Exposure to higher levels of LAN were associated with 21% higher risk of CMD (Summary risk ratio, SRR: 1.21, 95% CI = 1.16-1.27), accompanied by substantial heterogeneity (I = 61%; tau = 0.004; Cochran's Q = 41.02). Specifically, individuals in the highest category of LAN exposure exhibited 23% higher risk of obesity (SRR: 1.23, 95% CI = 1.14-1.32), 46% higher risk of diabetes (SRR: 1.46, 95% CI = 1.05-2.03) and 21% higher risk of other CMDs (SRR: 1.21, 95% CI = 1.10-1.34). Subgroup analyses revealed that the pooled-effect size of LAN and CMD was higher for indoor LAN than outdoor LAN (indoor LAN: SRR = 1.36; outdoor LAN: SRR = 1.17, P = 0.03). The overall quality was rated as moderate using GRADE guideline. Our study strengthens the evidence on the increase in CMD risk due to LAN exposure. Findings from this study have important implications for identifying modifiable risk factor of CMD, future prevention strategy development, and resource allocation for high-risk group. 2 2 2
