Genetics may play a role by predisposing certain individuals to exhibit tolerance to physiologic effects of alcohol early in their drinking careers thereby contributing to the establishment of heavier drinking patterns later in life. 21 Familial sources including both shared genetic and environmental may account for the early onset later dependence relation. 22 Persons who drink earlier may have physiologic changes that contribute to greater tolerance and the need to drink more to achieve the same pleasurable sensations after drinking. Persons who start drinking earlier in life may learn to drink in less controlled situations with peers whose drinking norms are to drink to intoxication rather than with family and parents whose norms might tend more towards moderate drinking. Second, there is also a need for research examining why even when diagnosis of alcohol dependence and measures of frequency of lifetime and past year heavy drinking are controlled, persons who began drinking at an earlier age are more likely to place themselves in situations that pose risk of injury.
Several explanations are possible.
Those who begin drinking at an early age may be less fearful of injury and situations that pose risk of injury. Some may derive pleasure or a sense of self-esteem by taking risks associated with injury. It is well known that persons who drive after drinking, for example, are more likely to speed and are less likely to wear seat belts. Alternatively, persons who start drinking at earlier ages may not be as aware or appreciate how alcohol increases injury risk. Other studies have shown that people who drive after heavy drinking are more likely to believe they can drive safely after higher amounts of alcohol consumption.