Light Exposure before Bedtime in Pregnancy is Associated with a Higher Risk of Gestational Diabetes

Abstract Introduction Evidence suggests a link between mistimed light exposure and impaired glucose regulation among nonpregnant adults, yet little is known about the magnitude and significance of evening light exposure during pregnancy. This study examined the relationship between evening light exposure before sleep, during pregnancy, and the incidence of gestational diabetes mellitus (GDM). Methods In this prospective cohort study conducted at 8 U.S. clinical sites, nulliparous women wore a wrist actigraphy monitor and completed a daily sleep diary for seven days between 160 and 216 weeks’ gestation. The primary exposure variable was time spent above 10 lux (dim light) during the three hours preceding sleep onset (“TAT10 pre-sleep”), averaged over valid days of recording and categorized to tercile groups (“High”, “Medium”, “Low”). Primary outcome variable was the incidence of GDM. Associations of TAT10 pre-sleep groups with baseline characteristics, sleep and activity variables were examined with Chi-squared and Kruskal-Wallis rank sum tests. Univariate and multiple logistic regression models were used to characterize the relationship between pre-sleep light exposure and GDM. Results 901 eligible women consented to participate; 758 submitted valid actigraphy recordings. Excluding women with pre-gestational diabetes and those with unknown gestational diabetes status, 741 were included in the analysis. Greater pre-sleep light exposure was associated with an increased risk of GDM (odds ratio [95% confidence interval]: 5.49 [1.8–23.84] in high and 4.05 [1.27–17.94] in medium vs 1 [reference] in low group). Women in the high group had more daytime light and were less likely to be late (midpoint > 5AM) or fragmented (wake after sleep onset ≥ 75th percentile) sleepers. Sleep duration, mean activity level, and light during sleep were not different between groups. After adjusting separately for age, body mass index, race/ethnicity, sleep duration, sleep midpoint, education, employment schedule, season, and daytime light exposure, pre-sleep light exposure remained significantly associated with GDM. Conclusion Increased evening light exposure in pregnancy may be an under-recognized, potentially modifiable risk factor for GDM. Future research should investigate light-targeted interventions as a potential preventive strategy for GDM. Support (if any) R01HL105549, nuMoM2b Network