Even moderate drinking may be related to higher iron levels in the brain - a potentially risky situation for memory and thinking skills, a new study suggests.
Researchers found that among nearly 21,000 middle-aged and older adults, those who drank as little as a few beers a week showed more iron accumulation in their brains than non-drinkers.
And iron buildup in certain brain areas correlated with weaker scores on tests of mental abilities like reasoning, planning and problem-solving.
It's not yet clear what it all could mean. But the findings add to evidence that there may be no "safe" level of drinking when it comes to brain health.
"Even small amounts of alcohol, within current alcohol guidelines, could harm your brain," said lead researcher Dr. Anya Topiwala of the University of Oxford in the United Kingdom.
The brain requires a certain level of iron to function normally, but the aging brain can accumulate an excess. And that excess iron has been linked to cognitive decline - a slow deterioration in memory and thinking skills that can lead to dementia.
Excess brain iron has also been found in people with alcohol dependence, according to Topiwala's team. But whether moderate drinkers might harbor more brain iron than non-drinkers has been unknown.
For the new study, the investigators turned to the UK Biobank, a research database with medical and genetic information on about 500,000 British adults aged 40 and older.
The researchers focused on just under 21,000 who had undergone MRI brain scans and reported on their average alcohol intake.
Overall, markers of brain iron were lowest in non-drinkers. And even moderate drinking - anything above four standard drinks a week - was tied to a greater accumulation of brain iron.
Higher brain iron, in turn, was linked to lower scores on tests of mental skills like planning, reasoning, reaction time and problem-solving.
The findings - published online July 14 in the journal PLOS Medicine - do not prove that alcohol directly raised brain iron or that brain iron was responsible for the lower test scores.
And the actual effects on test performance were small, according to Topiwala.
But they appeared to add to the effects of aging. As expected, Topiwala said, people's mental sharpness waned with age, and higher brain iron seemed to worsen that effect.
The findings add to evidence questioning whether lighter drinking is safe for the brain.
A study published in March, for example, found that people who drank regularly showed more age-related brain shrinkage than non-drinkers. Heavy drinking had the greatest impact, but even moderate levels - a few drinks per week - were tied to quicker brain atrophy.
But from a practical standpoint, there's no clear way to use the current findings, according to Dr. Kenneth Mukamal, who studies alcohol consumption and disease risk.
"This is an effort to look at one pathway - not a well-studied one - by which alcohol consumption could affect brain structure and function," said Mukamal, of Beth Israel Deaconess Medical Center in Boston.
"As a primary care clinician," he said, "knowing that alcohol does or does not associate with brain iron would not meaningfully impact recommendations I might make regarding alcohol use, which always should start with the current USDA (U.S. Department of Agriculture) guidelines."
Those guidelines say men should have no more than two alcoholic drinks per day, while women should limit themselves to one a day.
Valentinos Zachariou is a researcher at the University of Kentucky who studies the effects of excess brain iron.
He said that aging, itself, is the biggest contributor to increases in brain iron. That may be related to a breakdown in the blood-brain barrier (a border of specialized cells that keep toxins out of the brain), or changes in body cells that impair their ability to store iron.
At the same time, there could be ways to modify that aging effect.
In a study last year, Zachariou found that certain dietary nutrients correlated with both lower brain iron and better memory performance in a small group of older adults. Those nutrients included vitamin E and fatty acids found in foods like fish and nuts.
Zachariou said it's not clear "how concerned" people should be about the current findings. More research is needed, he said, to show whether moderate drinking, itself, raises brain iron, and to clarify the potential health significance.
Until then, he said, it wouldn't hurt to drink a little less beer, or add some fish to your diet.
If it is proven that alcohol harms the brain by raising iron levels, Topiwala said, that would raise the possibility of a treatment to minimize the damage.
"We already have iron chelators - medicines to reduce serum iron," Topiwala noted. "It's quite an intriguing possibility."
The U.S. National Institute on Alcohol Abuse and Alcoholism has more on alcohol's health effects.
SOURCES: Anya Topiwala, MD, PhD, senior clinical researcher, Nuffield Department of Population Health, University of Oxford, Oxford, U.K.; Kenneth Mukamal, MD, MPH, associate professor, medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston; Valentinos Zachariou, PhD, research scientist, Cognitive Neuroscience of Aging Laboratory, University of Kentucky, Lexington; PLOS Medicine, July 14, 2022, online