A twin study of genetic influences on diurnal preference and risk for alcohol use outcomes.

OBJECTIVE The population-based University of Washington Twin Registry (UWTR) was used to examine (1) genetic influences on chronobiology and (2) whether these genetic factors influence alcohol-use phenotypes. METHODS We used a reduced Horne-Östberg Morningness-Eveningness Questionnaire (rMEQ) to survey UWTR participants for diurnal preference. Frequency and quantity of alcohol use, as well as binge drinking (6+ drinks per occasion), were assessed on a 5-point Likert scale. Both diurnal preference and alcohol use were self-reported. Twin data were analyzed by using structural equation models. RESULTS The sample consisted of 2,945 participants (mean age = 36.4 years), including 1,127 same-sex and opposite-sex twin pairs and 691 individual twins. The rMEQ range was 4-25, with a mean score of 15.3 (SD 4.0). Diurnal "morning types" comprised 30.7% (N = 903) of participants, while 17.4% (N = 513) were "evening types." Regarding alcohol use, 21.2% (N = 624) reported never drinking. Among drinkers, 35.7% (N = 829) reported ≥ 3 drinks per occasion and 48.1% (N = 1,116) reported at least one instance of binge drinking. Genetic influences accounted for 37% of the variance in diurnal preference, with the remaining 63% due to non-shared environmental influences. Genetic propensities toward diurnal eveningness were significantly associated with increased alcohol quantity (β = -0.17; SE = 0.05, p < 0.001) and increased binge drinking (β = -0.19; SE = 0.04, p < 0.001), but not with frequency of alcohol use. Environmental paths between diurnal preference and alcohol use phenotypes were not significant. CONCLUSIONS Genetic influences on diurnal preference confer elevated risk for problematic alcohol use, including increased quantity and binge drinking. Differences in circadian rhythm may be an important and understudied pathway of risk for genetic influences on alcohol use.