Even Moderate Drinking May Be Bad For The Brain

In the ongoing alcohol-and-health debate, the evidence hasn’t been easy to parse

Picture: © Depositphotos.com/jakubdanek

Some studies have suggested that there's a measurable health benefit to having a little alcohol—one researcher even wrote an editorial suggesting that doctors tell their abstaining patients to start drinking a little for the health benefits. But other research has suggested that there’s no truly safe level of alcohol, since even light drinking is linked to health risks, including cancer. A study last month, for instance, suggested that even the equivalent of a small glass of wine per day is linked to an increased breast cancer risk. And a new study, out in the BMJ this week, throws some more evidence to that side of the debate: It finds that moderate drinking may also not be so innocuous when it comes to brain health.

As the authors of the new study point out, heavy chronic drinking is linked to Korsakoff syndrome and alcoholic dementia, but not much is known about the effects of lower levels of drinking—particularly “non-dependent” drinking, over time. To examine this question, the authors, from the University of Oxford and University College London, looked at data from the Whitehall II cohort study, which measured, among other variables, how much a person drank over 30 years (people were queried about every five years). Participants, 550 men and women who were not addicted to alcohol, also took cognitive tests periodically, and underwent brain scans with MRI at the end of the study period. The researchers looked for connections between alcohol consumption, cognitive function and brain structure.

It turned out that the heaviest drinkers—those drinking 30 units of alcohol per week—were at significantly higher risk of having atrophy in a brain region called the hippocampus, which is thought of as the most critical area for learning and memory, particularly verbal and spatial. But even moderate drinkers (14-21 units/week) were at a threefold risk of having atrophy in this region. Interestingly, light drinkers (up to seven units/week) didn’t seem to have any benefit over abstainers—they weren’t any increased risk, but there didn’t seem to be any protective effect of light drinking, as other studies have suggested. The study hinted that alcohol may affect the volume of the amygdala, but there were no changes in the prefrontal areas of the brain, which are responsible for higher-level thinking and executive function.

For heavier drinkers, there was also a slight drop in the “integrity” of the white matter, the connective tracts between cells that allow neurons to communicate. It’s not totally clear how these physical brain changes translate to function: The only change in cognition was that with increasing alcohol consumption, there was very slight decrease in performance on a test of semantic fluency, which measures how many words a person can generate in a particular category within a certain amount of time. There were no changes in the other cognitive functions tested.

The takeaway of the study seems to be that moderate drinking isn't without its own risks, at least when it comes to atrophy of the hippocampus. The hippocampus generally shrinks with age, and it’s a central area affected by Alzheimer’s disease. So anything that detracts from or contributes to its health as we age is important to be aware of.

It’s worth pointing out that this was an observational study, and the outcome was just a correlation—and despite the fact that the authors tried to control for as many confounding variables as they could, causation still can’t be assumed. There could be some other, as yet unknown, variable that was responsible for the connection between alcohol and brain health. Still, the participants were all living pretty healthy lifestyles, it's also true that the results observed here might be even more pronounced in the general population.

In the UK, where the study took place, alcohol guidelines have already been reduced, based on the accumulation of evidence about the risks. The U.S. has not done such a thing, at least not yet. Whether that will change is still up for grabs. In the meantime, it may be a good idea to keep drinking only very minimally and only if you already do—but to start drinking for the health benefits probably isn't wise. 

“Our findings support the recent reduction in UK safe limits,” write the authors, “and call into question the current U.S. guidelines, which suggest that up to 24.5 units a week is safe for men, as we found increased odds of hippocampal atrophy at just 14-21 units a week, and we found no support for a protective effect of light consumption on brain structure. Alcohol might represent a modifiable risk factor for cognitive impairment, and primary prevention interventions targeted to later life could be too late.”

Alice G. Walton, Contributor

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