The science on heavy drinking and the brain is clear: The two don't have a
healthy relationship. People who drink heavily have alterations in brain
structure and size that are associated with cognitive impairments.
But according to a new study, alcohol consumption even at levels most would
consider modest—a few beers or glasses of wine a week—may also carry risks
to the brain. An analysis of data from more than 36,000 adults, led by a
team from the University of Pennsylvania, found that light-to-moderate
alcohol consumption was associated with reductions in overall brain volume.
The link grew stronger the greater the level of alcohol consumption, the
researchers showed. As an example, in 50-year-olds, as average drinking
among individuals increases from one alcohol unit (about half a beer) a day
to two units (a pint of beer or a glass of wine) there are associated
changes in the brain equivalent to aging two years. Going from two to three
alcohol units at the same age was like aging three and a half years. The
team reported their findings in the journal Nature Communications.
"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 and faculty
member at Penn's Wharton School. He collaborated with former postdoc and
co-corresponding author Remi Daviet, now at the University of
Wisconsin-Madison, and Perelman School of Medicine colleagues Reagan
Wetherill—also a corresponding author on the study—and Henry Kranzler, as
well as other researchers.
"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,"
Ample research has examined the link between drinking and brain health, with
ambiguous results. While strong evidence exists that heavy drinking causes
changes in brain structure, including strong reductions in gray and white
matter across the brain, other studies have suggested that moderate levels
of alcohol consumption may not have an impact, or even that light drinking
could benefit the brain in older adults.
These earlier investigations, however, lacked the power of large datasets.
Probing massive quantities of data for patterns is the specialty of Nave,
Daviet, and colleagues, who have conducted previous studies using the UK
Biobank, a dataset with genetic and medical information from half a million
British middle-aged and older adults. They employed biomedical data from
this resource in the current study, specifically looking at brain MRIs from
more than 36,000 adults in the Biobank, which can be used to calculate white
and gray matter volume in different regions of the brain.
"Having this dataset is like having a microscope or a telescope with a more
powerful lens," Nave says. "You get a better resolution and start seeing
patterns and associations you couldn't before."
To gain an understanding of possible connections between drinking and the
brain, it was critical to control for confounding variables that could cloud
the relationship. The team controlled for age, height, handedness, sex,
smoking status, socioeconomic status, genetic ancestry, and county of
residence. They also corrected the brain-volume data for overall head size.
The volunteer participants in the Biobank had responded to survey questions
about their alcohol consumption levels, from complete abstention to an
average of four or more alcohol units a day. When the researchers grouped
the participants by average-consumption levels, a small but apparent pattern
emerged: The gray and white matter volume that might otherwise be predicted
by the individual's other characteristics was reduced.
Going from zero to one alcohol units didn't make much of a difference in
brain volume, but going from one to two or two to three units a day was
associated with reductions in both gray and white matter.
"It's not linear," says Daviet. "It gets worse the more you drink."
Even removing the heavy drinkers from the analyses, the associations
remained. The lower brain volume was not localized to any one brain region,
the scientists found.
To give a sense of the impact, the researchers compared the reductions in
brain size linked with drinking to those that occur with aging. Based on
their modeling, each additional alcohol unit consumed per day was reflected
in a greater aging effect in the brain. While going from zero to a daily
average of one alcohol unit was associated with the equivalent of a half a
year of aging, the difference between zero and four drinks was more than 10
years of aging.
In future work, the authors hope to tap the UK Biobank and other large
datasets to help answer additional questions related to alcohol use. "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."
They'd also like to be able to more definitively pin down causation rather
than correlation, which may be possible with new longitudinal biomedical
datasets that are following young people as they age.
"We may be able to look at these effects over time and, along with genetics,
tease apart causal relationships," Nave says.
And while the researchers underscore that their study looked only at
correlations, they say the findings may prompt drinkers to reconsider how
much they imbibe.
"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."
Reference:
Associations between alcohol consumption and gray and white matter volumes
in the UK Biobank, Nature Communications (2022).
DOI: 10.1038/s41467-022-28735-5