A number of epidemiological studies have shown that alcohol abuse or dependence is associated with major depression, according to background information in the article. However, it has previously been unclear whether one disorder causes the other, or whether a common underlying genetic or environmental risk factor increases risk for both.
Using data gathered from a 25-year study of health and development in New Zealand, David M. Fergusson, Ph.D., and colleagues at the Christchurch School of Medicine and Health Sciences, University of Otago, Christchurch, New Zealand, examined the associations between alcohol abuse and depression. A sample of 1,055 participants born in 1977 were assessed for both conditions at ages 17 to 18, 20 to 21 and 24 to 25 years and also asked questions about lifestyle and demographic factors.
At ages 17 to 18, 19.4 percent of the participants met criteria for alcohol problems and 18.2 percent for major depression; at ages 20 to 21, 22.4 percent had alcohol disorders and 18.2 percent major depression; and at age 24 to 25, 13.6 percent met alcohol disorder criteria and 13.8 percent had major depression. At all ages, alcohol abuse or dependence was associated with an increased risk of major depression-those who fulfilled criteria for alcohol abuse or dependence were 1.9 times more likely to also fulfill criteria for major depression.
Three models were tested to fit the data-one in which major depression and alcohol abuse disorders had a reciprocal association within time, a second in which alcohol disorders caused major depression and a third in which major depression caused alcohol disorders. "This analysis suggested that the best-fitting model was one in which there was a unidirectional association from alcohol abuse or dependence to major depression but no reverse effect from major depression to alcohol abuse or dependence," the authors write.
"The underlying mechanisms that give rise to such an association are unclear; however, it has been proposed that this link may arise from genetic processes in which the use of alcohol acts to trigger genetic markers that increase the risk of major depression," they continue. "In addition, further research suggests that alcohol's depressant characteristics may lead to periods of depressed affect among those with alcohol abuse or dependence."
The causal links also may include an increased risk of depression due to stressful life circumstances brought by alcohol problems, including social, financial and legal issues. "However, further research is required to elucidate the nature of the possible links between alcohol use and major depression," the authors conclude.