Study details and key findings

For the study, researchers examined data from nearly 560,000 adults in the U.S. Million Veteran Program and the U.K. Biobank. The researchers also examined genetic data from 2.4 million people who participated in 45 studies on dementia.

In the observational part of the study, the researchers found that people who reported consuming small amounts of alcohol (fewer than seven drinks a week) had a lower risk of dementia than people who reported being heavy drinkers (more than 40 drinks per week). Compared to light drinkers, heavy drinkers had a 41% higher risk of dementia, which increased to 51% among people with alcohol use disorder.

Interestingly, non-drinkers and people who reported never drinking had a similar risk of dementia as people who drank heavily.

However, when the researchers analyzed the genetic data, they found a steady rise in dementia risk with any increase in alcohol consumption. This genetics-based approach, known as Mendelian randomization, helped clarify whether alcohol itself drives dementia risk.

"The Mendelian randomization analyses give more confidence that alcohol — even in small doses — can cause an increase in dementia risk on a population level, rather than only for certain individuals," said the study's lead author Anya Topiwala, a senior clinical researcher in the department of psychiatry at the University of Oxford.

People who drank three alcoholic drinks per week had a 15% higher risk of dementia across their lifetime compared to those who only drank one alcoholic drink per week. A two-fold increase in the genetic risk of alcohol dependency was also associated with a 16% increase in dementia risk. 

Other experts said the results align with what's already known about how alcohol affects the brain.

"Neither part of the study can conclusively prove that alcohol use directly causes dementia," said Tara Spires-Jones of the University of Edinburgh. "But this adds to a large amount of similar data showing associations between alcohol intake and increased dementia risk, and fundamental neuroscience work has shown that alcohol is directly toxic to neurons in the brain."

Ultimately, Topiwala emphasized the urgency of prevention, noting that "despite great efforts, we still do not have accessible treatments to treat dementia and prevention is key. Alcohol consumption is widespread across the population, so our findings showing even small amounts of alcohol could increase dementia risk have great relevance."