Even light to moderate alcohol intake shows effects

Light to moderate alcohol consumption — as few as one or two drinks a day — was linked with reductions in overall brain volume, a cross-sectional study showed.

Among nearly 37,000 healthy adults in the U.K. Biobank, alcohol intake was negatively associated with global brain volume measures, regional gray matter volumes, and white matter microstructure, reported Reagan Wetherill, PhD, of the University of Pennsylvania Perelman School of Medicine in Philadelphia, and co-authors, in Nature Communications.

The link was stronger with greater alcohol consumption. As drinking increased from one alcohol unit (about half a beer) a day to two units (a pint of beer or a glass of wine) in 50-year-olds, for example, brain changes were equivalent to the effect of aging 2 years. An increase from two alcohol units to three showed changes equivalent to aging 3.5 years. Associations remained even when heavy drinkers were removed from the analysis.

“These findings contrast with scientific and governmental guidelines on safe drinking limits,” co-author Henry Kranzler, MD, of the Penn Center for Studies of Addiction, said in a statement.

“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,” Kranzler observed.

The study looked at alcohol intake and brain structure of 36,678 generally healthy adults ages 40 to 69 years in the U.K. Biobank who had data available as of September 2020. Participants completed questionnaires about demographic and health information, and a nurse conducted medical history interviews.

Participants self-reported the number of weekly or monthly alcohol units consumed in the past year, including wine, champagne, beer, cider, spirits, fortified wine, and other beverages. A pint or can of beer, lager, or cider was considered two alcohol units, a 25 mL single shot of spirits was one unit, and a standard 175 mL glass of wine was two units.

The analysis controlled for age, height, handedness, sex, smoking status, socioeconomic status, genetic ancestry, and county of residence. Brain imaging data included three structural assessments, resting and task-based fMRI, and diffusion imaging. Brain volumes were normalized for head size.

Nearly 90% of all regional gray matter volumes showed significant negative correlations with alcohol intake, and lower volume was not localized to any one brain region. The most extensively affected regions included the frontal, parietal, and insular cortices, with changes also in temporal and cingulate regions. In addition, associations were noted in the brain stem, putamen, and amygdala.

Drinking also was tied to lower coherence of water diffusion, lower neurite density, and higher magnitude of water diffusion, indicating less healthy white matter microstructure with increasing alcohol intake.

“Like individuals with alcohol use disorder, alcohol intake in this healthy population sample is associated with microstructural differences in superficial white matter systems functionally related to gray matter networks, including the frontoparietal control and attention networks, and the default mode, sensorimotor, and cerebellar networks,” Wetherill and co-authors noted.

Deeper white matter systems thought to be involved in cognitive functioning also were linked with alcohol intake, they added.

The research had several limitations: it was cross-sectional and based solely on middle-aged people of European ancestry. Reports of alcohol consumption were subject to reporting and recall bias, and the study did not account for people who may have had alcohol use disorder in the past. Reverse causality or potential confounding may have influenced results.

The researchers plan to use the U.K. Biobank and other large cohorts to help answer more questions about 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,” said co-author Gideon Nave, PhD, of the University of Pennsylvania Wharton School. “There’s some evidence that binge drinking is worse for the brain, but we haven’t looked closely at that yet.”

New longitudinal datasets that follow young people as they age may shed more light in the future, Nave added: “We may be able to look at these effects over time and, along with genetics, tease apart causal relationships.”