Onset of regular cannabis use and adult sleep duration: Genetic variation and the implications of a predictive relationship

Background: Limited evidence suggests that early cannabis use is associated with sleep problems. Research is needed to understand the developmental impact of early regular cannabis use on later adult sleep duration. Methods: In a sample of 1656 adult twins (56% female, Mean age = 25.79yrs), linear mixed effects models were used to analyze the influence of retrospectively assessed age of onset of regular cannabis use on adult sleep duration controlling for sex, depression, and current substance use. Twin analyses provided genetic and environmental variance estimates as well as insights into the association and potential casual relationships between these traits. Results: Earlier age of onset for regular cannabis use was significantly associated with shorter adult sleep duration on both weekdays (beta = -0.13, 95% CI = [-0.23, -0.04]) and weekends (beta = -0.18, 95% CI = [-0.27, -0.08]). Additive genetics significantly contributed to the onset of regular cannabis use (alpha(2) = 76%, 95% CI = [68, 85]) and adult weekend sleep duration (alpha(2) = 20%, 95% CI = [11, 32]). We found evidence of a significant genetic correlation (r(A) = -0.31, 95% CI = [-0.41, -0.15]) between these two traits and our best fitting model was consistent with early onset of regular cannabis use causing shorter adult weekend sleep duration (beta = -0.11, 95% CI = [-0.18, -0.03]). Conclusions: Our results are consistent with the hypothesis that early onset of regular cannabis use may have a negative impact on adult sleep duration.