As you sip that glass of beer, wine, or craft cocktail, you may be thinking you're getting a health boost, since researchers have been saying for years that moderate drinking has brain and heart benefits. But new studies—and new interpretations of old research—have cast doubt on that idea, and evidence about the effect on the brain of light to moderate drinking remains mixed.

A light drinker has no more than three drinks per week on average. Moderate drinking would be four to seven drinks per week for women and four to 14 drinks per week for men. Anything over that would be considered heavy drinking, according to the U.S. Centers for Disease Control and Prevention.

Among the studies that suggested health benefits for light to moderate drinking, a 2019 meta-analysis in the Journal of Alzheimer's Disease found that those who drank moderately reduced their likelihood of developing Alzheimer's disease by 28 to 39 percent compared with nondrinkers. In the Mass General Brigham Biobank study of 53,064 men and women, published in the Journal of American Cardiology in 2023, light to moderate drinking was linked to a 26 percent reduced risk of stroke. A large international study published in Neurology found that light drinking was associated with a 34 percent reduced risk of stroke in North America and Europe.

Research has not shown a link between drinking alcohol and the risk of developing Parkinson's disease or amyotrophic lateral sclerosis (ALS). That includes a large European study published in Movement Disorders in 2020, which tracked about 210,000 people and found no association with alcohol consumption in people who'd developed Parkinson's at the 12-year follow-up, and a review in the International Journal of Molecular Sciences in 2020, which concluded that further studies are needed to reach any conclusion regarding ALS and alcohol.

But the notion that light to moderate drinking could protect brain health has been challenged recently by findings from the UK Biobank, a large-scale database of individuals’ genetic and medical information. At least two different studies involving UK Biobank participants found an association between light and moderate drinking and shrinkage of the brain's gray matter and structural damage in white matter.

One of the studies, published last year in Nature Communications, showed that the impact worsens as alcohol intake increases. According to the other study, which lasted nine years and was published in NeuroImage: Clinical in 2022, brain MRIs of 23,378 participants showed that damage to white and gray matter could occur when people consume as few as four drinks per week.

Gray matter, critical for processing information, makes up most of the brain's outer layer. White matter, in the brain's interior, allows regions of gray matter to communicate with one another. “The more alcohol consumed, the smaller the volume of brain regions,” says the MRI study co-author Anya Topiwala, senior clinical researcher and consultant psychiatrist at the University of Oxford.

Dr. Topiwala's study did not find that brain changes necessarily corresponded to lower scores on cognitive tests, except in people with lower levels of education. “It could be the tests weren't sensitive enough to capture subtle cognitive problems,” says Dr. Topiwala. “Or they're too easy for people who are more highly educated, or our brains develop work-arounds.”

Certain factors also could influence the results showing that light to moderate drinking may protect against Alzheimer's and dementia. Those at higher socioeconomic levels can afford better-quality health care, which reduces dementia risk, says Louise Mewton, PhD, associate professor at the University of Sydney's Matilda Centre for Research in Mental Health and Substance Use, who researches the link between alcohol and dementia.

Another possible factor, particularly in studies of older people, is “selection bias”: Healthier people tend to volunteer for studies. And formerly heavy drinkers who now abstain are often included in the same category as never-drinkers, even though they may have residual damage to their brains from past alcohol use—which would skew findings that link abstaining from alcohol to higher likelihood of dementia. “With the data we currently have, it is really difficult to determine whether these confounding factors or alcohol itself are driving the lower risk of dementia among those who drink low-to-moderate amounts,” Dr. Mewton says.

Heavy drinking—for women, four or more drinks on any day or eight or more per week; for men, five or more drinks on any day or 15 or more per week—is linked to hundreds of health problems, including cirrhosis of the liver, heart disease, and various types of cancer, as well as to higher incidence of suicide, vehicular accidents, and violence, according to the National Institute on Alcohol Abuse and Alcoholism, which ranks heavy drinking as the seventh- leading cause of death and disability worldwide.

Alcohol use disorder, the medical term for heavy drinking (previously called alcoholism), was shown to triple the risk for dementia at any age and to be a leading cause of early-onset dementia, according to a five-year French study of about 31.6 million people published in The Lancet in 2018. The study noted many damaging effects of excessive drinking, among them that acetaldehyde, a substance produced when the body's enzymes break down alcohol, is toxic to brain cells and can lead to cell damage or loss and cause brain inflammation.

Additionally, people who develop a vitamin B1 deficiency may develop Wernicke-Korsakoff syndrome, a degenerative neurologic condition characterized by confusion, tremor, amnesia, and impaired vision and balance. Left untreated, the condition could lead to irreversible brain damage.

Heavy drinking raises blood pressure and can trigger atrial fibrillation, increasing the risk of stroke and vascular dementia. The effects of excessive alcohol consumption on the brain are visible on MRI scans, says Marlene Oscar-Berman, PhD, professor emerita at Boston University Chobanian & Avedisian School of Medicine. “In my research, we see atrophy [shrinkage] plus structure damage in certain brain regions in people with alcohol use disorder compared with healthy abstainers or light drinkers,” she says.

Studying MRI brain scans of 23 people with alcohol use disorder and 32 controls, Dr. Oscar-Berman found that connectivity—the ability of different regions of the brain to communicate with each other—is reduced. “These connectivity changes have been linked to problems with learning and memory, vision, language, and reasoning, and with the ability to plan and organize, regulate emotions, and respond appropriately to situations,” she says.

Alcohol use disorder also can make the brain look an average of 11.7 years older, according to a German study that compared MRI brain scans of 119 people with alcohol use disorder with those of healthy, age-matched light drinkers. While brain changes in the youngest alcohol users (ages 20 to 30) were not detected, the damage became apparent as people got older.

“Deciding to drink is a personal choice that should be determined by an evaluation of your family history and risk for health outcomes, as discussed with your doctor,” says Dr. Mewton.

In many countries, a federal health agency produces guidelines for alcohol use, and Dr. Mewton recommends that people follow them to minimize health risks overall. The Dietary Guidelines for Americans issued by the U.S. Departments of Agriculture and Health and Human Services advise limiting daily intake to no more than two drinks for men, one for women. As the guidelines state, “Drinking less is better for health than drinking more.”

Help for Alcohol Use Disorder

• Alcoholics Anonymous; 212-870-3400
• National Council on Alcoholism and Drug Dependence
• National Institute on Alcohol Abuse and Alcoholism; 301-443-3860
• Substance Abuse and Mental Health Services Administration; 800-662-4357