Brighter bedroom light at night predicts risk for earlier pubertal onset: a two-year longitudinal study

Abstract Context Light at night (LAN), as an environmental endocrine disruptor, can accelerate gonadal development in animals, but evidence in humans remains limited. Objective To investigate whether individual-level bedroom LAN exposure is associated with accelerated pubertal onset in boys and girls. Methods This prospective study was performed from September 2022 in Tianchang, Anhui province, China, investigated 886 boys and girls aged 6 to 10 years. Bedroom LAN exposure was recorded at one-minute intervals for two nights using a portable illuminance meter at baseline. Breast development for girls and testicular volume for boys were assessed at baseline and every 6 months for 2 years. Accelerated failure time (AFT) models were utilized to examine the associations between timing, intensity and duration of LAN exposure with earlier onset of puberty. Results Puberty started 3.84-month earlier among boys (TR, 0.96; 95%CI, 0.95–0.98) and 4.12-month earlier among girls (TR, 0.96; 95% CI, 0.94–0.98) in the highest LAN exposure group compared to the lowest exposure group. Each 30-minute increase in the duration of LAN exposure ≥ 3 lx was associated with an 9% higher risk of earlier testicular development in boys (HR, 1.09; 95% CI, 1.02–1.16), and a 12% higher risk of earlier thelarche in girls (HR, 1.12; 95% CI, 1.07–1.16). Notably, the increased risk was more pronounced with post-bedtime light (PBL) exposure compared to pre-awake light (PAL) exposure. Discussion These findings suggest an accelerating effect of individual-level LAN exposure on pubertal onset in both boys and girls, particularly during the post-bedtime period.