A new study does not support the belief that alcohol consumption causes depression - nor that it prevents it. This was the conclusion of clinical neuroscientists from the University of Western Australia (UWA).
They write about their findings in a paper published online recently in the journal Molecular Psychiatry.
In their paper, the authors describe how research has linked alcohol use, particularly alcohol abuse and dependence, to raised risk for depression.
They also note that current practice for diagnosing depression implies the link is causal.
However, they say the evidence has come only from studies that are not designed to determine cause and where unexplored factors can interfere with the results, as Professor Osvaldo Almeida, lead author from UWA's School of Psychiatry and Clinical Neurosciences, explains:
Contrary to previous studies, researchers found that alcohol neither causes nor prevents depression.
"Even one of the diagnoses we have for depressive disorders - Substance Induced Mood Disorder - is a diagnosis where alcohol plays a role. However, because of the observational nature of the association between alcohol and depression, and the risk of confounding and bias that comes with observational studies, it is difficult to be entirely certain that the relationship is causal."
For example, he says heavy drinkers may also be heavy smokers, have poor diets and other health problems, and these factors could explain why so many also suffer with depression.
Given the logistic and ethical problems of conducting a trial of alcohol use to prevent depression, Almeida and colleagues decided to use another approach to find if there was a causal link, by exploring it through a genetic pathway.
Gene variant not linked to depression
It is well established that certain gene mutations affect the amount of alcohol that people drink, and that one in particular - a variant of the Alcohol dehydrogenase 1B (ADH1B) gene - is linked to metabolism of alcohol.
The ADH1B gene variant produces a version of the ADH1B enzyme that makes the body up to 80 times less efficient at breaking down alcohol, with the result that people who carry the variant are much less tolerant of the substance. In fact, recent studies have found they are also far less likely to have alcohol-related disorders.
Almeida explains how a "triangular study" looking at this genetic variant, alcohol use and depression can help determine if there is a causal link between alcohol and depression:
"Now, if alcohol causes depression, then a genetic variation that reduces alcohol use and alcohol-related disorders, should reduce the risk of depression. The great advantage of looking at the gene is that this association is not confounded by any other factors - people are born like that."
For their study, the team used data collected over 3 to 8 years from 3,873 elderly men taking part in the long-running Health in Men Study (HIMS).
The results showed - as expected - that the ADH1B gene variant was linked with reduced consumption of alcohol, but there was no association whatsoever with depression.
Prof. Almeida says:
"The conclusion is that alcohol use neither causes nor prevents depression in older men. Our results also debunk the view that mild to moderate alcohol consumption may reduce the risk of depression."
He believes the link that observational studies have found between alcohol use and depression is probably explained by other factors, not a direct result of the alcohol itself.
This has been suggested before, even by studies that propose alcohol use raises depression risk.
For instance, a 2009 report in the JAMA journal Archives of General Psychiatry that describes how a statistical model shows alcohol abuse may lead to depression risk rather than vice versa, suggests the raised risk for depression could in part be due to the stress brought on by alcohol problems, including social, financial and legal issues.
The authors concluded there was a need for more studies to examine the "possible links between alcohol use and major depression."
In the meantime, Prof. Almeida urges these findings do not mean it is safe for people to consume alcohol "in whatever way they like." He notes there are lots of other health problems that are known to result from excessive use of alcohol. Their new study just shows that depression is not one of them, he adds.