Consuming 4 Alcoholic Drinks a Week Might Increase Risk for Cognitive Decline, According to a New Study

Unless you're currently dealing with, have history of or are concerned about a potential addiction,* there are several proven health benefits to drinking alcohol—in moderation, that is.

The technical meaning of "moderate drinking" is up to one drink per day (5 ounces of wine, 12 ounces of beer, 1 ounce of alcohol) for women and up to two drinks per day for men, according to the National Institutes of Health. Health experts have debated if it's time to change what "moderate" means, though, pointing to studies like one in the September 2017 edition of JAMA Psychiatry that reported, "the level of alcohol consumption that minimized harm across health outcomes was zero standard drinks per week."

A new study adds to the stack of evidence that suggests it might be time to shift how much we believe is safe to sip. According to a July 2022 study in the journal PLOS Medicine involving more than 20,000 people in the United Kingdom, drinking more than four standard alcoholic drinks per week can change iron levels in the brain enough to increase risk for cognitive decline.

What This Alcohol Study Found

To come to this conclusion, Anya Topiwala, Ph.D., a senior clinical researcher at the University of Oxford's Nuffield Department of Population Health, and her team analyzed data from more than 20,000 individuals enrolled in the UK Biobank. The medical records of the Biobank include self-reported alcohol consumption and magnetic resonance imaging results.

Since earlier studies have linked high levels of iron in the brain with neurodegenerative diseases such as Parkinson's disease and Alzheimer's as well as slower executive function, lower fluid intelligence and slower reaction times, this team compiled MRI results for levels of iron in the brain. They then compared that with the average number of drinks each participant said they consumed.

"We found that drinking alcohol was linked to higher levels of iron in the brain. These higher brain iron levels in turn were linked to worse performance on memory tasks," Topiwala tells EatingWell.

This appears to be the first study to directly correlate increased brain iron levels with even just moderate alcohol consumption. Participants who drank more than seven units of alcohol per week displayed increased levels of brain iron, Topiwala and team found.

Translating this common UK measurement, Roxana Ehsani, RD, CSSD, a registered dietitian nutritionist in Miami and a national media spokesperson for the Academy of Nutrition and Dietetics says, "one unit is equal to one shot, one glass of wine equals 2 units, and a can of beer is about 2.4 units."

The results of this study build on March 2022 research in Nature Communications that also used UK Biobank info to discover that consuming one to two drinks per day may reduce brain volume. On the flip side, a January 2020 review in Nutrients reports that light to moderate drinking may reduce risk for dementia as we age. So clearly, more research is needed.

But for now, Topiwala says the moral of the story is that "drinking even 'moderately' may harm your brain. Cutting down drinking is the safest thing to do," she says.

So is any level of alcohol "safe" when it comes to cognitive decline? "That's tricky! Based on these findings, we did not find drinking four to seven units a week led to higher brain iron," Topiwala says, so six units or fewer (so up to three glasses of wine or two beers) might not have an impact. "However, in our previous work, we suggested there may not be a safe level."

That said, "there are limitations with this study as with many others," Ehsani says, including the fact that drink levels are self-reported and the pool of participants might not match the demographics of the global average. "Therefore more research needs to be conducted before new guidelines can be established."

The Bottom Line

This research found that drinking seven units or more of alcohol per week might be enough to increase brain iron levels to a point that could lead to cognitive decline. The Dietary Guidelines for Americans still recommend no more than one drink a day for women, and two drinks a day max for men, so aim to consume below that threshold—and, if you ask Topiwala, the fewer drinks the better.

Until we learn more and confirm these results in more studies, Ehsani says that if you enjoy a glass of wine a few times each week, it should be A-OK to "continue to drink in moderation. If you find yourself having more than a glass or two per night, consider cutting back."

Instead of always having a cocktail or glass of wine for happy hour (then with dinner), try a nonalcoholic mixed drink, a nonalcoholic beer, NA wine or sparkling water, Ehsani suggests.

*If you are struggling with your relationship with alcohol (or if a loved one is), visit samhsa.gov or aa.org for support and treatment options near you.