Study: Even One Glass of Alcohol Daily May Shrink the Brain

Is drinking a beer every day doing you more harm than good? According to a new study published in the journal Nature Communications, it might be.

An international team of researchers found that drinking alcohol was linked to a decrease in gray and white matter in the brain. People who had a heavy amount of alcohol consumption per day were at the greatest risk for shrinkage. However, the researchers also observed reductions in brain volume even if people drank just one drink a day.

But James Giordano, PhD, MPhil, a professor in the departments of neurology and biochemistry at Georgetown University who was not involved in the study, cautioned not to mix up brain volume with brain function. In other words, a decrease in brain volume is not correlated with a decrease in how your brain works. 

“Is social drinking directly harmful to the brain? The consensus is not in the short term. And there may even be certain benefits that we recognize, such as antioxidants in red and white wine,” Giordano told Verywell. “But there is a threshold for the extent [alcohol] has a negative impact that’s going to have a meaningful effect on the capability and function of the brain. An individual having one or two drinks a few times a week is on the lower end of the spectrum.”

The good news is that many of the shorter-term changes in brain structure and function—impairments in movement, decision-making, and slow reaction time—are reversible once you stop drinking. However, Giordano says there is a point when individuals who drink a moderate to heavy amount of alcohol over a long period of time may experience real changes.

“The important issue here is how much alcohol you’re drinking daily. And as that number goes up, then clearly the daily effect is going to go up,” Giordano said. “Then what you’re seeing is an increase in the probability for at least some structural changes. Those structural changes can then lead to functional changes that can be durable over time...Now we’re talking years, and then many of the changes in the brain that could occur from alcohol use may be permanent.”

Alcohol Linked to Reduction in Brain Matter

The researchers studied the brains of 36,678 European adults between the ages of 40 to 69. All adults in the study had no preexisting conditions. Every adult reported their average alcohol consumption with one to two drinks a day considered light drinking and over four drinks considered heavy drinking.

“What you’re really looking at is the iterative cumulative effects of alcohol ingestion across a range of doses over a period of time,” Giordano explained. “They’re not talking about an individual who has one drink, for example on Monday, and then has a drink on Thursday. They’re talking about an individual who has one drink per day over a year.”

Men drank more glasses a day than women did, but the reduction in brain volume was similar. However, brain imaging picked up decreases in gray and white matter volume in the brains of people who regularly drank alcohol. Gray matter contains most neuronal cell bodies and is important in the processing of information in the brain. White matter comprises millions of axons—the part of the neuron that sends information to other brain cells—and is involved in communication across multiple brain areas.

While people with high alcohol consumption showed the greatest reduction in gray and white matter, the team noticed decreases among people who had only one alcoholic drink a day.

What Does It Mean?

What's behind the shrinkage? Giordano said the most likely explanation is the dehydrating effect of alcohol and dehydration over time from repeated alcohol use. He explained that if you’ve ever felt thirsty while drinking alcohol, it’s because alcohol pulls water from between tissue and cells. This also happens in the brain where white matter, the connective parts of the brain, houses axons loaded with water.

The decrease in water may explain the decrease in white matter and gray matter. Giordano noted that people who drank the highest daily amounts may experience both dehydration and neurotoxic effects since the reduction in brain volume occurred in key areas involved in brain networking.

The reductions in brain volume were present in several different regions of the brain. The findings suggest alcohol’s effects on brain volume are widespread rather than concentrated in a single region.

On a deeper level, decreases in white matter extended to fibers and tracts within white matter regions such as the fornix—an area where messages are sent out of the hippocampus. The hippocampus is one brain region in communication with other areas of the brain to process memory and learning. Previous research has linked changes in white matter in the fornix to heavy alcohol drinking and memory problems.

The study authors may have found a statistically significant change in brain volume for people who drank only one glass, but Giordano says that does not equate to a change or loss in brain function. Giordano added that future research should focus on how a decrease in brain volume impacts the function of nerve cells and how that translates to overall brain function.

Previous research has found that changes in brain volume are associated with a decrease in cognition. “One thing we would be concerned about is the connectivity of nerve cells, which then decreases their capacity for network activity,” Giordano said. “This will then be evidenced in potential changes in cognition, emotion, and behavior.”

Study Limitations

The brains of adolescents and adults respond differently to alcohol, even if it’s just one drink. Because the study only studied the brain health of middle-aged Europeans, there is a possibility that the findings differ by age and that there may be more damage in younger people who drink.

The researchers also used self-reported data about how much participants drank per day. This leaves the possibility that people may have inaccurately overestimated or underestimated how much they had to drink.

The study design also influences how people should interpret the results. It is difficult to measure a person’s drinking habits, including their past relationship with alcohol. Therefore, it is difficult to control for other outside factors that could have caused or influenced the changes in gray and white matter in the brain.

For example, some people who drank very little alcohol in the past year could have had abused alcohol in the past, leaving the possibility that the neurological changes were already there before the past year. Other factors they did not control for included the type of drink or the amount of alcohol in each drink—a person who took two shots of Everclear may have drunk more alcohol than someone drinking four cans of hard seltzer.

The Dangers of Drinking Too Much

Drinking too much alcohol can cause permanent damage to your central nervous system. It can also increase your risk of depression, anxiety disorders, and cause inflammation in the brain.

Heavy alcohol consumption may also indirectly cause a brain disorder called Wernicke-Korsakoff syndrome (WKS). Giordano explains that excessive drinking impairs the GI tract and can completely block the absorption of thiamine (vitamin B1)—an essential vitamin that’s important for the nervous system to carry out its job.

Because of the disruption in thiamine absorption, there is a depletion of thiamine in the brain, which snowballs into your nerve cells not functioning correctly. A person with WKS may experience severe memory impairments, extreme confusion, and problems with eyesight.

“Alcohol has a potentially harmful and toxic effect and therefore should be indulged with caution,” Giordano warned.

To cut back on drinking, you should try to make gradual changes rather than quit cold turkey. Some suggestions include:

• Swapping your drink with another but with less alcohol in it
• Alternating a drink of alcohol with water or a non-alcoholic beverage
• Setting a budget on how much alcohol you’re willing to spend for a night
• Creating a plan on how much alcohol you’re drinking that night 
• Reducing your alcohol intake a little each day