A team of researchers from Washington University and from the Queensland Institute of Medical Research in Brisbane, Australia, studied 5,974 twins born between 1902 and 1964 who were part of the Australian Twin Register. They also spoke with 3,814 of those twins' spouses for the study, published in the May issue of the journal Alcoholism: Clinical & Experimental Research.
"As they say, 'like marries like,'" says first author Julia D. Grant, Ph.D., research assistant professor of psychiatry at Washington University. "Spouse selection is not a random process, and we call this non-random mating. People tend to choose mates who are similar to them, not only from the same neighborhood or socio-economic background but also alike in personality and other behaviors. We found that people at risk for alcohol dependence tend to marry others who are at risk."
Alcohol dependence is influenced by both genetic and environmental factors. Genetic influences explain about half of the variance in a person's total risk for alcohol dependence. The other half of an individual's risk for alcohol dependence comes from environmental factors — such things as employment, interests, friends and family.
"There's lots of room for different factors to influence the behavior of two people who are married," Grant says. "One spouse could work at a place where the co-workers go out for a drink after work. Or one spouse could be a regular churchgoer, while the other prefers to sleep."
Another aspect of the environment is the drinking behavior of one's partner. The researchers found that the impact of the partner's drinking depends on whether it's examined along with non-random mating. Once the researchers accounted statistically for the fact that "like marries like," they saw that the additional influence of the partner's behavior tended to reduce the likelihood of problem drinking. Grant says that although non-random mating means that a person with genetic risks for alcohol problems will tend to marry another with a propensity toward alcohol dependence, it appears that when one spouse begins to abuse alcohol, the other might actually reduce alcohol intake.
"We don't really know how this works," she explains. "It is possible that an individual decreases his or her alcohol consumption in reaction to the other's excessive alcohol use. Maybe one person is responsible for getting the kids up and out for school in the morning, for example."
Grant says she hopes soon to study how spouses might influence not only each other's risk of alcohol dependence but also other psychiatric disorders, such as depression and how those factors interact. And she says as more is learned about these risks, it's important to let people know what they're up against.
"Education is a key to reducing risk for alcohol dependence," she says. "Regardless of genetic risks, there are other detrimental environmental factors associated with alcohol, including reduced educational attainment and income, fewer social and neighborhood support networks, higher rates of divorce and single parenthood and exposure to other psychiatric problems. We need to make people aware of all of their risks, so they can take steps to protect themselves."
Grant JD, Heath AC, Bucholz KK, Madden PAF, Agrawal A, Stratham DJ, Martin NG. Spousal concordance for alcohol dependence: evidence for assortative mating or spousal interaction effects? Alcoholism: Clinical & Experimental Research, vol. 31 (5), pp. 717-728, May 2007.
DOI: 10.1111/j/1530-0277.2007.00356.x
This research was supported by was supported by the National Institute on Alcohol Abuse and Alcoholism of the National Institutes of Health.
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