Alcohol abuse has long been associated with depression and other detrimental health effects. However in moderation the consumption of alcohol, specifically wine, has also been linked to health benefits, particularly relating to cardiovascular health. Miguel Martínez-González from the University of Navarra, Spain and colleagues investigated whether alcohol can also have a protective effect on the risk of developing depression. Their results, published in a recent study in BMC Medicine, reveal that the relationship between alcohol and depression is less clear cut that previously thought. Martínez-González explains more on how the amount and type of alcohol consumed has a bearing on the likelihood of depression.
This study is part of the Prevención con Dieta Mediterránea (PREDIMED) study, what is this and how did it come about?
The PREDIMED trial is a multicenter, randomised primary cardiovascular prevention trial using Mediterranean diet. During 2002, following a call for proposals by the Spanish government, different Spanish investigators working in nutrition from different perspectives joined forces to start a research network. We applied together for a grant to start a large randomised trial to test the effectiveness of a Mediterranean diet on the ‘primary’ prevention of cardiovascular disease
What led you to look at the association between alcohol consumption and depression?
There is a hypothesis that some risk factors and mediator mechanisms are shared by depression and coronary heart disease. This hypothesis prompted our research on common dietary exposures for both depression and coronary heart disease. It is well known that moderate alcohol consumption is related to lower risk of coronary heart disease.
You found that consuming low to moderate amounts of wine, in the range of two to seven drinks per week, was associated with a lower risk of depression. Why do you think this might be?
The mechanistic explanations on how alcohol in low to moderate amounts may prevent unipolar depression are largely unknown. Moderate ethanol intake is known to increase serum high-density lipoprotein cholesterol, and to exert beneficial effects on endothelial function and inflammation. These mechanisms are likely to be involved not only in coronary heart disease but also in depression. We thought that the higher concentration of active polyphenols in wine may account for higher protection by wine than by other alcoholic beverages. In addition, moderate alcohol drinking has a GABAergic effect, acting on GABAA receptors, that may prevent or counteract the effects of depression on this system.
Previous studies have found a direct association between alcohol consumption and symptoms of depression. Why do you think your results differ?
The direct association between alcohol intake and risk of depression in previous studies was only seen at higher levels of ethanol intake, i.e. only with heavy drinking. But most of our participants who were drinkers, only consumed low to moderate amounts of alcohol. In fact, when we assessed the risk among those who drank more than 40 g/day of alcohol, we found that they were at higher risk, but this association was not statistically significant, probably due to the small number of heavy drinkers in our cohort. The differential characteristics of our study population need to be taken into account, because participants in the PREDIMED trial were an older, traditional Spanish Mediterranean population, who consumed chiefly wine, and mainly in a context of socialisation with family or friends. Subjects with problematic use of alcohol were explicitly excluded from this trial.
Why do you think the effect on the risk of depression was more pronounced with wine consumption in comparison to other alcoholic drinks?
The stronger inverse association for wine may be due in part to the lower average quantity of ethanol consumed among drinkers, but it can specially be strengthened by the presence of considerable amounts of polyphenols in wine. In this line of thought, wine consumption has also previously been related with stronger beneficial cardiovascular effects. In addition, preferentially wine drinkers are known to be at lower risk of becoming heavy drinkers.
Is it possible that there are alternative factors which may explain your results?
A potential alternative explanation might be that wine drinkers are healthier than non-wine drinkers in other aspects. But this is not likely to be a very likely explanation in our study, because we took into account the potential confounding effects of these factors, including lifestyle variables, health indicators and dietary intervention, and adjusted for them. Another potential alternative explanation might be related to different patterns of consumption among wine-drinkers than in other drinkers. In fact, preference for wine drinking has been associated with a less concentrated pattern of consumption, and this can account for a healthier pattern of consumption that avoids binge drinking with its potential harmful neurotoxic effects.
What are the implications of these findings and what further research is needed?
The implications are that moderate alcohol drinking, specifically in the form of wine, may represent a means of preventing unipolar depression; but further prospective studies and trials are needed to confirm our findings.
Questions from Joanna Denyer, Senior Assistant Editor for BMC Medicine and Stephanie Harriman, Deputy Medical Editor for BioMed Central.