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

Experimental models suggest that in utero photoperiod influences circadian regulation and systems tied to later-life anxiety, depression, and addiction. Whether in utero photoperiod is associated with mental health and substance use in adolescents and young adults remains unknown. 10,721 full term born children from the GUTS cohort contributed to these analyses. Total photoperiod was calculated by summing daily light hours across 280 gestational days using each offspring's exact birth date and state. We used multivariable adjusted generalized estimating equations, logistic regression, and linear regression to estimate odds ratios (ORs) and mean differences (MDs) for self-reported mental health and substance use outcomes across quintiles of in utero photoperiod. We observed no association between in utero photoperiod and mental health outcomes. Marijuana, opioids, stimulants, and alcohol use also did not differ by photoperiod. However, offspring in the top versus bottom photoperiod had lower odds of ever smoking [MV-OR Q5vsQ1 , 0.89; 95% CI: 0.80,0.99; P = 0.08], smoked fewer cigarettes per day [MV-MD Q5vsQ1 , −0,16; 95%CI: −0.29,-0.04; P = 0.02], and showed lower nicotine dependence [MV-MD Q5vsQ1 , −0,46; 95%CI: −0.8,-0.12; P = 0.007]. No sex interactions were observed for mental health; for smoking and marijuana, males had lower odds of use. In utero photoperiod was not associated with mental health. Greater prenatal light exposure was linked to reduced smoking, but not alcohol or marijuana use, in offspring. Further research should examine cumulative prenatal and postnatal photoperiod effects on these outcomes. • In utero photoperiod showed no link with offspring mental health • Greater in utero light exposure was associated with lower odds of smoking • Longer in utero photoperiod was linked to fewer cigarettes and less dependence • No association found with alcohol, marijuana, or stimulant use