Huge UK Study Shows Even Light Alcohol Consumption Can Still Cause Brain Shrinkage in Adults

Key Points: 

• Analysis of thousands of U.K. middle-aged and older adults shows increased alcoholic beverages consumed per day is linked to decreased brain volume. 
• Predictions show that people who consume 2 drinks per week have brains that are 10 years older than people who do not drink. 
• Alcohol consumption is associated with damaging parts of the brain important for memory, attention, and cognition. 

Drinking alcohol can be fun, but it’s also a toxin that poisons our body and brain. As they say, the occasional drink is fine, but how many drinks can we have before our brain starts to deteriorate?

A new study published in Nature Communications by Daviet and colleagues from the University of Pennsylvania showed that having just one drink a day could cause our brain to shrink. The Penn scientists analyzed the drinking habits and brain scans of thousands of participants from the United Kingdom (U.K.) to find that drinking one or more alcoholic beverages per day is associated with having less brain matter and predicted that having too many drinks could age the brain by up to 10 years. They also found an association between alcohol consumption and damage to regions of the brain associated with cognition.

Notably, changes in brain structure were observed in individuals who consume between 1 and 2 units of alcohol daily, which is between ½ and 1 alcoholic drink. (The UKB assessment defined units of alcohol as follows: a pint or can of beer/lager/cider = two units; a 25 ml single shot of spirits = one unit; and a standard glass of wine (175 ml) = two units.)

“These findings contrast with scientific and governmental guidelines on safe drinking limits,” says Kranzler, who directs the Penn Center for Studies of Addiction. “For example, although the National Institute on Alcohol Abuse and Alcoholism recommends that women consume an average of no more than one drink per day, recommended limits for men are twice that, an amount that exceeds the consumption level associated in the study with decreased brain volume,”

These findings help confirm that having that extra drink might not be such a good idea. 

Drinking More Alcohol is Associated with Less Brain Matter 

It probably does not surprise anybody that chronic alcohol use isn’t healthy, as it is associated with cardiovascular disease, nutritional deficiency, cancer, and accelerated aging. It is also associated with brain shrinkage (atrophy). Some studies even suggest that the effect of alcohol consumption and aging on brain size interact, meaning that drinking too much alcohol as we age could accelerate the deterioration of our brain.  

However, much of what we know about the deleterious effects of alcohol consumption on the brain are from studies on individuals with alcohol use disorder (AUD) – individuals who are unable to stop drinking despite the negative consequences. There is limited research on individuals who consume alcohol that do not have AUD, much of which is inconclusive, likely due to a small number of participants. 

By using the data from the UK Biobank, the largest collection of high-quality MRI brain scans and alcohol-related behaviors, Daviet and colleagues were able to work with data from a large number of participants (large sample size) without AUD.  

The study includes 36,678 healthy middle-aged and older adults (52.8% female) from the UK aged 40 to 69 years. “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,” says Gideon Nave, a corresponding author on the study. 

From the brain scans, Daviet and colleagues quantified the levels of gray and white matter from each participant’s brain. Gray matter composes the portions of the brain not enriched with fat, mostly the cell bodies of neurons. White matter represents the connections in our brain, as the axons of our neurons are sheathed in fat (fat is white) to promote incredibly fast electrical signals that transmit information from one region of the brain to another. 

The results of this large-scale analysis revealed that both gray and white matter brain volume decreased as a function of daily alcohol intake. Separating the data by daily alcohol consumption shows the non-linear nature of changes in brain structure.

“It’s not linear,” says Daviet, the lead author of the study. “It gets worse the more you drink.”

Even Light Alcohol Consumption Predicted to Accelerate Aging 

As part of their analysis, Daviet and colleagues predicted how much gray and white matter would be lost in the average 50-year-old if they were to increase their alcohol intake. Since the volume of our brain decreases with aging naturally, the Penn scientists were able to compare the equivalent age at which that volume would be lost due to age. In other words, they were able to predict how many years the brain would age in response to increased alcohol intake. For example, increasing intake from 0 to 4 units (0 to 2 drinks) per day, was predicted to decrease the volume of the brain to a size equivalent to aging the brain 10 years. 

Alcohol Damages Cognition Associated Regions of the Brain 

In addition to brain volume changes, Daviet and colleagues analyzed brain structural (microstructural) changes. One of the brain regions most highly associated with increased alcohol consumption was the fornix – the main connection between other regions of the brain and the hippocampus, the part of the brain that forms new memories. Damage to the fornix has consistently been associated with heavy alcohol consumption and memory impairments. The East Coast researchers also found a strong relationship between alcohol consumption and damage to regions of the brain associated with attention and cognitive function. These results are similar to the studies of AUD individuals.

Limitations of the Study 

Overall, Daviet and colleagues confirm many of the brain deteriorating effects of drinking one too many alcoholic beverages. This study has a large dataset giving it high statistical power and reliability, but it does have its limitations. One of these limitations is that all the participants are of European ancestry, specifically individuals living in the UK. Also, all the participants are middle-aged and older adults. Future studies can be more generalizable by including different age groups from all over the world. Another limitation is that the study cannot identify causal effects. Reverse causality is therefore a possibility. This means that there is a possibility that individuals with smaller brain volumes tend to drink more. 

Who Should Drink Less?

This is the first large-scale study to analyze individuals who don’t necessarily have a drinking problem. In other words, the study analyzes individuals who voluntarily chose to drink. One of the main findings is that just one, or even half a drink a day could lead to decreases in brain volume. The consequences of this decrease in brain size were not analyzed (and it would be difficult to do so), so it is unclear how much of an effect a small decrease in brain volume would have on our behavior and ability to think and feel. There could also be other effects of alcohol, other than brain size that are beneficial, but this was also not measured and would also be difficult to tease out. 

Some individuals, especially the younger crowd do not necessarily drink every day, but drink a lot on one or two days of the week, like the weekend. This could hypothetically be a lot worse than drinking throughout the week. “This study looked at average consumption, but we’re curious whether drinking one beer a day is better than drinking none during the week and then seven on the weekend,” Nave says. “There’s some evidence that binge drinking is worse for the brain, but we haven’t looked closely at that yet.”

Another key finding was the non-linear relationship between the number of drinks consumed and the volume of brain matter lost, meaning that a little more alcohol could lead to a lot more brain loss. “There is some evidence that the effect of drinking on the brain is exponential,” says Daviet. “So, one additional drink in a day could have more of an impact than any of the previous drinks that day. That means that cutting back on that final drink of the night might have a big effect in terms of brain aging.” In other words, Nave says, “the people who can benefit the most from drinking less are the people who are already drinking the most.”