Age at first drink and its influence on alcohol use behaviours in young adulthood: Evidence from an Australian household-based panel study

Background: Public health guidelines recommend delaying the initiation age for alcohol. However, the causal link between age-at-first-drink (AFD) and future alcohol use in young adulthood is uncertain. This study examined the association between AFD and alcohol-related outcomes at age 20 years using an Australian sample. Methods: Data were obtained from Waves 1-19 (years 2001-2019) of the Household, Income and Labour Dynamics in Australia Survey on 20-year-olds with responses across >= 3 consecutive waves (n = 2278). The AFD for each respondent (between 15 and 20 years) was analysed relative to Australian legal drinking age (18 years). Inverse probability treatment weighting was used to evaluate associations between AFD and four outcomes at age 20 years: risk of current alcohol use; quantity of weekly alcohol consumption; risk of binge drinking; and frequency of binge drinking. Adjustments were made for confounders (e.g., heavy drinking by parents). Robustness of study findings was evaluated using several diagnostic tests/sensitivity analyses. Results: Among 20-year-olds, those with an AFD of 15-16 years consumed significantly more alcohol per week compared to an AFD of 18 years. Additionally, 20-year-old drinkers with an AFD of 16 years were significantly more likely to binge drink (though this association was likely confounded). An inverse dose-response relationship was observed between AFD and weekly alcohol consumption at 20 years, where a higher AFD led to lower alcohol consumption. Conclusion: Study findings indicate an association between a higher AFD and consuming less alcohol in young adulthood, which could potentially support the scale-up of prevention programs to delay AFD among Australian adolescents.