This study tested a third mechanism via which age at 1st drink may be related to AD symptoms – according to this hypothesis, the extent to which genetic and environmental factors influence AD symptoms differs in those with earlier versus later age at 1st drink – in other words, age at 1st drink moderates/interacts with the extent to which genetic and environmental factors influence liability to AD symptoms. Evidence supporting this hypothesis was obtained by showing that heritable factors for AD symptoms are more pronounced in those who start drinking at an early age. However, in those who initiated their drinking careers later in life, especially during early adulthood, individual differences in their AD symptomatology was largely due to those environmental factors that are unique to each individual (and measurement error). The implication of this model, from a public health standpoint, is that encouraging adolescents to delay their initiation of alcohol consumption may serve to buffer the expression of familial predisposition to later alcohol-related problems.
