Imbibing just a handful of beers a week is associated with long-term changes to a person’s brain, a new study finds — although the functional meaning of these changes is unclear.

Why it matters:

While it’s widely accepted that drinking too much is bad for you, conventional wisdom — and the government’s dietary guidelines — says that alcohol can be consumed in moderation. The US government defines that as one drink a day for women and two for men.

This study, published in the BMJ on Tuesday, finds that drinking around these levels — 8 to 12 drinks a week — is associated with a few measures of cognitive decline that showed up on brain scans.

The nitty-gritty:

Researchers brought 550 Londoners to Oxford and ran them through an MRI machine. But these weren’t just any Londoners — they were government employees who, about every five years since 1985, had been filling out surveys about their health habits, including how much alcohol they consumed. This enabled the researchers to look for relationships between the individuals’ drinking habits and what showed up on their brain scans.

The researchers found that moderate drinking over those 30-plus years was associated with degeneration and shrinking of the hippocampus, a region of the brain involved in memory and navigation, as well degeneration of the brain’s white matter.

In essence, “the more people drank, the smaller their hippocampus,” said first author Anya Topiwala, a psychiatry professor at University of Oxford. Consuming one more alcoholic drink per week was associated with a 0.01 percent decrease in the size of the hippocampus. For comparison, aging one year was associated with a 0.02 percent decrease.

But keep in mind:

The study only looked at a few hundred Londoners, mostly well-educated and middle-class, so it may not be representative of a wider population. Topiwala also pointed out there might have been “selection bias” in the sample — individuals had to get from London to Oxford in order to undergo the MRI scans and then spend an hour in a brain scanning machine and undergo other memory tests — which individuals who were alcohol dependent or had suffered brain damage from alcohol use might be less likely to do.

The authors also noted that the changes in the hippocampus are only statistically significant for the right hippocampus, not the left hippocampus. Topiwala said she’s not sure why this is the case.

What they’re saying:

In an accompanying editorial, Killian Welch, a neuropsychiatrist at a hospital in Scotland, wrote that the study might change what we think constitutes a healthy level of drinking.

“[The] findings strengthen the argument that drinking habits many regard as normal have adverse consequences for health,” Welch wrote. “This is important. We all use rationalizations to justly persistence with behaviors not in our long term interest. With publication of this paper, justification of ‘moderate’ drinking on the grounds of brain health becomes a little harder.”

The bottom line:

Alcohol has an effect on your brain, perhaps at lower levels than previously thought.

Republished with permission from STAT. This article originally appeared on June 6, 2017