The Queensland Institute of Medical Research (QIMR) and the Royal Prince Alfred Hospital have determined that although alcohol consumption and alcohol dependence are closely related, the causes of susceptibility are not necessarily the same.
This new study found that variation in long-term average alcohol intake is almost entirely due to genetic differences.
A study in the August issue of Alcoholism: Clinical & Experimental Research looks at genetic and environmental causes of variation in long-term alcohol consumption, and estimates what degree of overlap may exist with causes of susceptibility to alcohol dependence. Results indicate that variation in long-term average alcohol intake is almost entirely due to genetic differences, and that some genes affect both intake and dependence while others affect only dependence.
"Alcohol consumption is about how much a person drinks at some particular time, whereas alcohol dependence is more about the effects of alcohol on a person - their behaviour, their neurophysiology, and their relationships," said John Whitfield, first author of the study and senior scientist at the RPA Hospital and part-time QIMR research fellow. "Most people in western societies consume alcohol but only some consume it in large enough quantities to cause harm," said Whitfield, "similarly, only some are so affected by it that they meet the psychiatric criteria for 'alcohol dependence.' There may not be a relationship between intake and dependence, except during bouts of uncontrolled and extremely heavy drinking, or there may be some overlap or common causes for each, or the same underlying causes for both. The study sought to explore this relationship, which has received little attention in the past because most studies have concentrated on either one or the other."
Using twin studies, QIMR scientists have examined items of alcohol consumption as well as possible diagnoses of alcohol dependence. "In the people we studied, alcohol intake was reasonably constant across time as a person who reports high intake at one time is likely to report high intake at other times," said Whitfield. "However, we were able to show that variation between people in their long-term average intake is almost entirely due to genetic differences between people. Secondly, we found that higher reported alcohol intake, at any of the three times studied, was associated with a higher probability of alcohol dependence at some time in a person's life. The association was mainly due to genetic effects on both alcohol intake and alcohol dependence, but our results also show that some genes affect only dependence."
Whitfield noted that one of the strengths of this study is its examination of long-term averages of intake. It is the long-term average which is important for both the harmful physical effects of alcohol and its association with decreased cardiovascular risk. The differences between people which do persist across time, or the differences in long-term average intake, appear to depend on genetic differences between them.
Researchers are hopeful that this research may help to change perceptions of alcoholism. "Naturally enough," he said, "public attention focuses on the most extreme forms of alcohol dependence and literary and dramatic portrayals of 'alcoholics' shape or reinforce this view. However, people with less extreme forms of alcohol dependence also report many alcohol-related problems, including relationship and employment difficulties.
From this study we can see more clearly that certain people are born with an increased risk of developing alcohol problems. An individual who is aware of a family history of alcohol-related problems needs to take efforts to reduce their own risk of problems, and society needs to provide support by reducing its tacit approval of heavy drinking.