Brighter Bedroom Light at Night Predicts Risk for Earlier Pubertal Onset: A 2-Year Longitudinal Study

Light at night (LAN), as an environmental endocrine disruptor, can accelerate gonadal development in animals, but evidence in humans remains limited.

To investigate whether individual-level bedroom LAN exposure is associated with accelerated pubertal onset in boys and girls.

This prospective study was performed from September 2022 in Tianchang, Anhui province, China, and investigated 886 boys and girls aged 6 to 10 years. Bedroom LAN exposure was recorded at 1-minute intervals for 2 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 models were utilized to examine the associations between timing, intensity, and duration of LAN exposure with earlier onset of puberty.

Puberty started 3.84 months earlier among boys [time ratio (TR): 0.96; 95% confidence interval (CI): 0.95-0.98] and 4.12 months 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 a 9% higher risk of earlier testicular development in boys [hazard ratio (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 postbedtime light exposure compared to preawake light exposure.

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.