Alcohol Dependence and Habitual Smoking : Risks

by National Institute of Health

Smoking and alcohol dependence frequently occur together, and both behaviors are determined in part by genetic influences. The Collaborative Study on the Genetics of Alcoholism (COGA), which is investigating the genetic factors contributing to alcohol dependence, also allows for analyses of the genetic factors determining smoking. Using a sample comprised of alcoholics and their closest (first-degree) relatives as well as a community-based control sample, COGA investigators found that both alcohol dependence and habitual smoking were transmitted within families. This familial transmission resulted from both common and drug-specific influences, which likely include genetic factors. Further genetic studies (candidate gene studies and genomic screening approaches) have identified several DNA regions that may contain genes that confer a susceptibility for alcoholism. Some of those genes also may contribute to the risk for habitual smoking.

In the United States, excessive alcohol use is a serious public health problem. At some time in their lives, 19 percent of men and 8 percent of women have been diagnosed with alcohol dependence as defined in the American Psychiatric Association's (APA's) Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV). Moreover, 6 percent of men and 3 percent of women have experienced symptoms of alcohol dependence in the past year. Unfortunately, the prevalence of alcohol dependence has been increasing among younger people, indicating that alcohol dependence may become an ever more prominent public health problem. In addition to causing numerous serious medical disorders (liver and heart disease), alcohol dependence is associated with costly, adverse social consequences, such as disruption of families, crime, traumatic accidents, and lost productivity. As a result, the annual costs related to alcohol dependence in the United States for 1998 have been estimated at $185 billion.

At the same time, 25 percent of the U.S. adult population can be classified as current smokers. Although the prevalence of smoking has decreased during the past 30 years, little change in smoking rates has occurred since the mid-1990s. More worrisome, smoking rates have increased among adolescents and young adults in the United States, accompanied by a dramatic increase in tobacco use worldwide. Smoking is a leading cause of preventable disability and death and is associated with multiple well-documented adverse health effects, including heart disease, pulmonary disease, and various cancers. The economic burden of smoking is high. Thus, the annual costs attributable to smoking in the United States have been estimated to be $50 billion in direct medical costs plus a similar amount in lost productivity.

Alcohol dependence and smoking frequently occur together. Smokers, including those who are nicotine dependent, have an elevated risk for alcohol dependence. Thus, smokers in general have a 2.1 times greater risk and nicotinedependent smokers have a 2.7 times greater risk of becoming alcohol dependent compared with nonsmokers. Similarly, alcohol-dependent people have a greatly increased risk of smoking than do non-alcohol-dependent people.

Both alcohol dependence and smoking are complex behaviors that are influenced by environmental as well as genetic factors. Various types of research, including studies of identical and fraternal twins, adoptees, and families with multiple alcoholic members have provided evidence for a strong genetic component in the development of alcohol dependence. Based on these findings, the heritability of alcohol dependence has been estimated at 64 percent. Similarly, twin studies have supported the role of genetic influences on smoking, suggesting a heritability of 60 percent for nicotine dependence. Because alcohol dependence and smoking frequently co-occur and because genetic factors influence both behaviors, twin studies have examined the extent to which both addictions might share some genetic risk factors. These analyses found evidence of a substantial overlap in genetic factors influencing nicotine and alcohol dependence. These data support a common underlying genetic vulnerability to both alcohol and nicotine dependence.

Another study that has assessed the genetic factors contributing to alcohol dependence and has enabled researchers to investigate the relationship of those factors with the genetic factors determining smoking is the Collaborative Study on the Genetics of Alcoholism. This article provides a brief overview of COGA and its design as well as highlights of some of the study's results regarding the prevalence of smoking in families of alcohol-dependent people. In addition, the article discusses specific genetic associations between alcohol and nicotine dependence that have been identified by analyzing specific genes (candidate genes) or by screening study participants' entire genetic material (the genome).

Description of COGA

COGA is a comprehensive study conducted at multiple sites across the United States to detect and map genes that confer a susceptibility for alcohol dependence and related disorders, including dependence on other drugs (nicotine). The study initially recruited alcohol-dependent people and their family members, thereby obtaining a sample of people at high risk for both alcohol-use disorders (alcohol abuse and alcohol dependence) and smoking. This sample allows COGA investigators to study the relationship between alcohol dependence and smoking among family members.

To obtain their sample, the investigators first recruited alcohol-dependent patients (also called index cases or probands) who were treated in both inpatient and outpatient chemicaldependency treatment centers. The investigators obtained the probands' permission to contact first-degree relatives and invited those family members to participate in the study. In addition, the study included a community-based comparison group that was recruited from a variety of sources, such as dental clinics, health maintenance organizations, and a driver's license registry. Control families with alcohol-dependent family members were not excluded from the study. This comparison group provided baseline measurements of alcohol dependence and related characteristics in the general population.

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.