Adolescent Drinking Behavior and Genes

by National Institute of Health

Many people begin to consume alcohol and establish drinking patterns during adolescence, making this an important developmental period for alcohol researchers to study. Both drinking initiation and establishment of drinking patterns are influenced to varying degrees by genetic as well as environmental factors. Using twin studies conducted in Finland and other countries, researchers have analyzed the specific genetic and environmental influences as well as the gene - environment interactions that shape drinking behavior in adolescence. These studies indicate that drinking initiation is determined primarily by environmental influences, whereas the establishment of drinking patterns is determined mostly by genetic factors, which themselves are subject to moderation by the environment.

The years between early adolescence and young adulthood are a crucial period for alcohol researchers to study, because drinking typically is initiated during adolescence, and by young adulthood, individual differences in established drinking patterns are evident. The earliest stages of alcohol use merit particular attention because research has suggested that the initiation of alcohol use must be distinguished from the frequency, quantity, and density (i.e., the number of drinks consumed in a certain length of time) of alcohol use once drinking is initiated. Consequently, analyses in adults with already established drinking patterns can explain only part of the mechanisms and contributing factors underlying the development of alcohol abuse and dependence. To obtain a more comprehensive explanation of these processes, it also is necessary to study the factors influencing drinking initiation.

Another reason to focus on early adolescent drinking comes from research evidence indicating that people who begin drinking at an earlier age have a heightened risk for negative consequences of drinking, such as alcohol abuse or alcohol dependence. For example, interviews of adults consistently and convincingly have shown a strong association between an early initiation of drinking and later alcohol-related problems: People who report drinking as early as age 13 or 14 are much more likely to exhibit alcohol-related behavior problems in adulthood than people who began drinking at a later age. The association of drinking problems with earlier age of initiation is particularly strong in people with a family history of alcoholism, but also exists in people without a family history.

But what is the relevance of this association? In most cases, it is hazardous to draw a causal connection based on such observations. Thus, it is possible that drinking initiation at an earlier age is causally related to greater vulnerability to alcohol's cumulative effects. Alternatively, early onset of drinking and a greater likelihood of later problems may simply be correlated - that is, they are independent signs or symptoms of people who are at elevated risk of alcohol dependence. In the latter case, prevention efforts designed to promote delays in age of drinking initiation would do little to reduce the prevalence of adult alcoholism - an issue that is important to resolve. One approach to doing this is to conduct longitudinal studies that follow, over several years, genetically informative samples, such as samples of twins who differ in their age at onset of drinking.

This article reviews recent findings from two ongoing longitudinal twin studies conducted in Finland that elucidate the contributions of genetic and environmental influences to initiation of drinking and later trajectories of alcohol use and abuse. Data from these population-based FinnTwin studies help investigators address questions about factors contributing to various stages of alcohol use. The resulting research has underscored the importance of the concept of dynamic gene - environment interactions.

The General Role of Genetic and Environmental
Factors in Alcohol-Related Behavior

Both genetic and environmental factors contribute to the different stages in a person's drinking history. The factors that influence individual differences in whether, and at what age, drinking is initiated are different in kind from the factors that influence individual variations in patterns of drinking, once the acute subjective effects of alcohol ingestion are experienced. Moreover, it is clear from numerous studies that although genetic factors have some influence on drinking behavior, the effects of genetic differences between people can be enhanced or reduced by variations in the environments in which the people live - that is, there are gene - environment interactions.

A person's susceptibility to developing alcohol dependence and other alcohol- related problems manifests as an unfolding developmental process that involves both genetic and environmental factors and is continuously modulated by gene - environment interplay. This concept of a complex developmental process is supported by fundamental findings in recent behavior-genetic research that have profoundly altered the earlier view that people are passive players who mechanically mirror their environmental experience. Instead, recent research findings indicate the existence of extensive gene - environment correlations, whereby people are active agents who help create the experiences to which they are exposed, selectively seek environments to match their specific dispositions, and modify their environments through their actions. In short, new research suggests that constant gene-by-environment interplay is involved in the development of alcoholism risk over time.

To understand the factors affecting the development of alcoholism, it is essential to appreciate this continuing interaction of genetic and environmental influences (e.g., how a child's behavioral dispositions interact with that child's household environment). Similarly, it is important to acknowledge that the household environment does not stand alone, but is "nested" within neighborhoods, schools, communities, and cultures. Accordingly, the ways in which a child expresses his or her internal dispositions are modulated by the adult models, parenting practices, peer interactions, access to alcohol, and school and neighborhood environments to which the child is exposed. All of these factors either enhance or reduce the risk for alcoholism that results from the child's genetic makeup.

About the Author

NIH is the nation's medical research agency - making important medical discoveries that improve health and save lives. The National Institutes of Health (NIH), a part of the U.S. Department of Health and Human Services, is the primary Federal agency for conducting and supporting medical research.