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. KEY WORDS: adolescent; young adult; age of onset; AOD (alcohol and other drug) use initiation; AOD use pattern; genetic theory of AODU (alcohol and other drug use); hereditary factors; environmental factors; hereditary vs. environmental factors; social environmental risk and protective factors; family risk and protective factors; longitudinal study; twin study; monozygotic twin; dizygotic twin; the FinnTwin studies; Finland; Collaborative Study on the Genetics of Alcoholism (COGA)
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 (Grant and Dawson 1997). 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. …