Early-life light exposure and mental health and substance use outcomes in adolescence and young adulthood.

Offspring with the highest in utero photoperiod had lower odds of ever smoking compared to those with the lowest photoperiod exposure.

• Multivariable-adjusted OR for top versus bottom quintile of photoperiod: MV-ORQ5vsQ1 = 0.89; 95% CI: 0.80, 0.99
• P-value = 0.08 for the quintile comparison of ever smoking
• Analysis was conducted using generalized estimating equations with multivariable adjustment
• Study population was 10,721 full-term born children from the GUTS cohort

Offspring with the highest in utero photoperiod smoked fewer cigarettes per day compared to those with the lowest photoperiod exposure.

• Mean difference for top versus bottom quintile: MV-MDQ5vsQ1 = -0.16; 95% CI: -0.29, -0.04
• P-value = 0.02
• This finding was statistically significant at conventional thresholds

Offspring with the highest in utero photoperiod showed lower nicotine dependence compared to those with the lowest photoperiod exposure.

• Mean difference for top versus bottom quintile: MV-MDQ5vsQ1 = -0.46; 95% CI: -0.8, -0.12
• P-value = 0.007, the strongest statistical association observed in the study
• Nicotine dependence was a self-reported outcome

In utero photoperiod was not associated with mental health outcomes in adolescents and young adults.

• No association was observed between in utero photoperiod and mental health outcomes across quintiles of photoperiod exposure
• No sex interactions were observed for mental health outcomes
• Outcomes were self-reported and analyzed using multivariable adjusted generalized estimating equations, logistic regression, and linear regression

In utero photoperiod was not associated with marijuana, opioid, stimulant, or alcohol use.

• Marijuana, opioids, stimulants, and alcohol use did not differ by photoperiod quintile
• For smoking and marijuana use, males had lower odds of use in sex-stratified analyses
• No sex interactions were observed for mental health outcomes, but sex differences were noted for smoking and marijuana

Total in utero photoperiod was calculated by summing daily light hours across 280 gestational days using each offspring's exact birth date and state.

• The study included 10,721 full-term born children from the Growing Up Today Study (GUTS) cohort
• Photoperiod exposure was categorized into quintiles for analysis
• Offspring birth date and state of residence were used to calculate photoperiod
• Experimental models suggesting that in utero photoperiod influences circadian regulation provided the biological rationale for the study