Associations between timing of secondhand smoke exposure and sleep disorders: National Chinese Children Study.

Background: Previous studies have shown that current secondhand smoke exposure increases the risk of sleep disorders. However, evidence of different time windows of secondhand smoke exposure and childhood sleep disorders remains scarce. We aimed to evaluate the time-varying associations between secondhand smoke exposure and childhood sleep disorders in China.

Methods: We recruited 188,090 children aged 6 to 18 years from Liaoning, Guangdong, and Xinjiang, China between April 2012 and May 2018. Secondhand smoke exposure and sleep disorders were assessed via parent- or guardian-completed questionnaires, with sleep disorders evaluated through the Sleep Disturbance Scale for Children (SDSC). Generalized linear mixed models were used to evaluate the association between time-varying secondhand smoke exposure and sleep disorders, with false discovery rate correction for multiple comparisons.

Results: Prenatal, postnatal, or current exposure to secondhand smoke was associated with greater total t-sleep scores and a higher likelihood of sleep disorders after false discovery rate correction, especially among children exposed from the prenatal period through childhood. These children had higher total t-sleep scores (β = 4.48; 95% CI, 4.32, 4.65) and higher odds of sleep disorders (OR = 2.28; 95% CI, 2.12, 2.45). Additionally, each 5-unit increase in cigarette exposure was associated with a 0.97-point (β = 0.97; 95% CI: 0.91, 1.02) increase in total sleep t-score.

Conclusions: Secondhand smoke exposure at different time windows, especially exposure from prenatal to childhood, and higher family smoking frequency, was associated with an increased risk of sleep disorders in children. These findings highlight the need for a smoke-free home environment to support sleep healthy in children.