How Alcohol Shrinks Your Brain With Just One Drink per Day

Even moderate alcohol consumption leads to reduced gray matter volume.
no to alcohol

Heavy alcohol consumption and the human brain have been proven not to have a healthy relationship. The connection between drinking and brain health has been studied extensively.

While solid evidence shows that people who drink heavily have alterations in brain structure, including brain atrophy, neuronal loss, substantial reductions in grey and white matter across the brain, other researchers have found that moderate alcohol intake may have little effect on the brain or even that mild drinking may improve the brain in older populations. However, the new research shows that the association grew stronger just as the level of alcohol consumption increased.

The evidence has been conflicting

drunk man sitting at the bar

An analysis of data from over 36,000 adults, generally healthy middle-aged and older adults from the UK, was conducted in a new study. A team of scientists from the University of Pennsylvania led the study, and the findings were published in the journal Nature Communications. The result shows that alcohol consumption, even at levels most would consider modest, may carry risks to the brain. They discovered a connection between drinking and lowered brain volume, stating that an average intake level of one alcohol unit a day – approximately half a beer can result in less brain activity. They also stated that the association between alcohol and the brain grew stronger just as the level of alcohol consumption increased.

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For instance, an average increase in drinking – among individuals 50 years old – from one alcohol unit a day to two units (a glass of wine or a pint of beer) reveals brain alterations are equivalent to two years of aging. At the same age, going from two to three alcohol units was like aging three and a half years. 

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It was necessary to adjust for unobserved heterogeneity that could cloud probable associations between drinking and the brain. The team considered age, handedness (individual’s preferential use of one hand), height, smoking status, sex, genetic ancestry, socioeconomic status, and county of residence. They also adjusted the brain-volume data to account for the overall head size.

The Biobank’s volunteer members had answered survey questions on their alcohol usage levels, ranging from complete abstinence to an average of four or more units per day. When the researchers divided the subjects into groups based on their average consumption levels, they noticed a subtle but noticeable pattern: the gray and white matter volume that the features of other individuals might otherwise predict was lowered.

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Going from zero to one alcohol unit per day did not affect brain volume, but going from one to two -or two to three units a day – was linked to reductions in gray and white matter.

“It’s not linear,” Daviet says. “The more you drink, the worse it becomes.”

Even when the heavy drinkers were excluded from the analysis, the correlations remained. The scientists discovered that the reduced brain volume was not restricted to a single brain region. The researchers compared the changes in brain size associated with drinking to those associated with aging to feel the impact.

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total alcohol consumption per capita litres of pure alcohol
Credit: OurWorldInData.org

According to their modeling, each additional unit of alcohol consumed per day resulted in a more significant aging effect in the brain. While moving from zero to one drink per day was linked with a half-year of aging, going from zero to four drinks was connected with more than ten years of aging.

Does the large sample size work?

Previous research lacked the power of large datasets. However, Nave, Daviet, and colleagues have previously conducted studies using the UK Biobank, a dataset of genetic and medical information from half a million UK middle-aged and older persons, to look for patterns in large data sets. They used biomedical data from this resource in the current work, especially brain MRIs from over 36,000 adults in the Biobank, which can help determine white and gray matter volume in various brain areas.

“Having this dataset is like having a more powerful microscope or telescope,” Nave explains. “With a higher resolution, you can see patterns and connections that you couldn’t see previously.”

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“The large sample size is a big help. It allows us to identify minor connections, even between drinking half a beer and one beer a day,” explains Gideon Nave, a contributing author on the study and faculty member at Penn’s Wharton School.

Research vs. governmental guidelines

The findings from the research contradict scientific and governmental recommendations for safe drinking limits,” explains Kranzler, the director of the Penn Center for Studies of Addiction. “For instance, while the National Institute on Alcohol Abuse and Alcoholism advises that women should take an average of one drink daily, the recommended drink limit for men is twice that, which is higher than the consumption level connected to lowered brain volume in the study.

Future research

The authors hope to use the UK Biobank and other large datasets in future research to answer further concerns about alcohol usage.

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“We’re intrigued if drinking one beer per day is better than drinking none during the week and then drinking seven on the weekend,” Nave explains. Although we haven’t looked into it yet, there’s some indication that heavy drinking is bad for the brain.”

They’d also like to prove causes rather than association, which could be achievable with new longitudinal biological datasets that track young people as they grow older. 

“We may be able to consider these effects over time and, with genetics, separate causal relationships,” Nave explains.

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While the scientists explained that their study focused solely on associations, they believe the findings may cause drinkers to reassess their consumption levels.

“Some evidence suggests that drinking has an exponential effect on the brain,” Daviet explains. “So, one additional drink in a day may have a greater effect than any of the previous drinks consumed that day. It means cutting back on that last drink of the night could have a significant impact on brain aging.” 

In other words, Nave explains, “those who can benefit the most from drinking less are the ones that are already drinking the most.”

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