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Experts recommend women limit their alcohol intake to one glass a day. Westend61/Getty Images
  • Experts recommend that women limit alcohol intake to one drink a day and men limit it to two drinks a day.
  • However, researchers say that even a single drink on average per day can decrease brain volume over time.
  • Their study showed that a 50-year-old who drinks a pint of beer or a glass of wine a day effectively ages their brain by 2 years.
  • Experts note, though, that heavier drinking has a more substantial impact on brain size.

A drink a day could shrink your brain away, a new study suggests.

Heavy alcohol use has long been associated with changes in the brain. However, researchers from the University of Pennsylvania have found that even light to moderate drinking — as little as a glass of beer or wine daily — is associated with reduced brain size and structure.

Such changes could be warning signs of cognitive impairment, the researchers warned.

The researchers’ report, based on an analysis of data about drinking and brain health among more than 36,000 people, likened the changes in brain volume among drinkers to aging.

For example, a 50-year-old who on average drinks a pint of beer or a glass of wine once a day effectively ages their brain by two years, according to findings published in the journal Nature Communications.

And those who consume an average of 4 drinks daily had brains that were 10 years “older” than those who did not drink.

“The fact that we have such a large sample size allows us to find subtle patterns, even between drinking the equivalent of half a beer and one beer a day,” said Gideon Nave, a corresponding author on the study and faculty member at the University of Pennsylvania’s Wharton School.

The findings suggest that even drinking at levels considered “safe” in government guidelines may not be benign, researchers said.

For example, the National Institute on Alcohol Abuse and Alcoholism (NIAAA) sets safe drinking levels as one drink daily for women and two daily drinks for men. Consumption at either of those levels causes detectible, harmful changes in the brain, the study authors wrote.

“Our presumption of what is a safe level of drinking is inadequate,” said Dr. Henry Kranzler, a study co-author and the director of the Center for Studies of Addiction at the University of Pennsylvania’s Perelman School of Medicine. “The NIAAA limits are probably higher than they should be, perhaps by a factor of two given our findings.”

The changes were small at low drinking levels — going from zero to one alcohol units or averaging half a drink daily didn’t change brain volume significantly. But both gray and white matter in the brain was noticeably reduced as consumption climbed to a drink a day or higher.

“It gets worse the more you drink,” said Remi Daviet, a study co-author and an assistant professor at the University of Wisconsin-Madison.

“If you limit your focus to the brain, it’s probably not all that concerning if someone is having a drink a day versus half a drink,” said Kranzler. “As it gets above that, the risk gets more substantial.”

“I’m a lover of good wine,” Kranzler added. “These findings have led me to rethink [how much I drink]. I didn’t welcome this news, but I’d rather have my brain.”

The researchers controlled for various factors that could have skewed the results, including age, height, left and right-handedness, sex, smoking status, socioeconomic status, genetic ancestry, county of residence, and — for the brain-volume data — overall head size.

Future research will look at whether the brain changes are permanent or related to binge drinking or general alcohol consumption rates.

“We’re curious whether drinking one beer a day is better than drinking none during the week and then seven on the weekend,” Nave said. “There’s some evidence that binge drinking is worse for the brain, but we haven’t looked closely at that yet.”

Alcohol use reduces brain volume by causing brain cells and cells in their connective tissue to expel water, said James Giordano, PhD, a professor of neurology and biochemistry at the Georgetown University Medical Center in Washington, D.C.

“What we see is a systemic desiccating effect, but loss of volume doesn’t necessarily mean loss of function,” he told Healthline. “It doesn’t mean one drink will be harmful for you. But repeated or high-volume consumption of alcohol is going to have problematic effects.”

Kranzler said that while the desiccating effects of alcohol could be the root cause of some of the brain damage observed in the study, researchers also observed changes in the integrity of white matter that are unlikely to be related to dehydration.

The old saying about drinking “killing brain cells” isn’t quite accurate, said Giordano, “but it can disrupt their function.”