Drinking by parents, siblings, and friends as predictors of regular alcohol use in adolescents and young adults: a longitudinal twin-family study.

AIMS The aim of this study was to examine whether the drinking habits of parents, siblings, and friends were related to regular drinking in adolescents and young adults, cross-sectionally as well as longitudinally. METHODS Data of 12-30-year-old twins from the Netherlands Twin Register were analysed. Information on regular drinking was collected in 1993, 1995, and 2000. Logistic regression analyses were conducted on cross-sectional data of 1993 (N=3760), short-term longitudinal data of 1993-95 (N=2919), and the long-term longitudinal data of 1993-2000 (N=1779). RESULTS Results show that age, sex, and one's own previous drinking habits were important predictors of later-life regular drinking. Drinking habits of parents showed small but persistent positive associations. Alcohol use of the co-twin was strongly related to alcohol use of the participants, especially in the cross-sectional analyses, while alcohol use of additional siblings other than the co-twin was relatively unimportant. Cross-sectionally, friends' alcohol use showed a high association with regular drinking, but this association decreased over time. CONCLUSION Cross-sectional analyses showed that a substantial part (29%) of the variance in regular drinking habits of adolescents and young adults was explained by the drinking habits of family members and friends, in particular, by drinking of co-twins and friends. But, over time, drinking by family members and friends could only explain a relatively small part (4-5%) of the variance in adolescents' and young adults' alcohol use.