Any amount of alcohol consumption may increase dementia risk, according to a new large-scale study.
The findings challenge the belief that light or moderate drinking might protect brain health, with genetic evidence suggesting harm at all levels.
A threefold increase in weekly drinks raised dementia risk by 15 per cent.
Scientists combined observational data from more than half a million participants in the US Million Veteran Program and UK Biobank.
They also studied genetic drinking patterns across 2.4m people in 45 separate studies.
The research team described their work as the most comprehensive investigation into alcohol and brain health to date.
“Genetic evidence offers no support for a protective effect – in fact, it suggests the opposite,” said Dr Anya Topiwala, senior clinical researcher at Oxford Population Health and consultant psychiatrist, who led the study.
“Even light or moderate drinking may increase the risk of dementia, indicating that reducing alcohol consumption across the population could play a significant role in dementia prevention.”
The study found that every three extra alcoholic drinks consumed per week raised the likelihood of dementia by 15 per cent.
This dose-dependent effect was seen at all levels of drinking, with no safe threshold identified.
Researchers used Mendelian randomisation, a method that analyses genetic variations to clarify cause-and-effect relationships.
This helps remove confounding factors that often complicate observational research, such as lifestyle differences between drinkers and non-drinkers.
Dr Joel Gelernter, professor at Yale University and senior author, said the results would have clinical implications: “Medical knowledge seemed to previously support that some light drinking could be beneficial to brain health.”
Dr Stephen Burgess, statistician at the University of Cambridge, added: “The random nature of genetic inheritance allows us to compare groups with higher and lower levels of alcohol drinking in a way that allows us to make conclusions that untangle the confusion between correlation and causation.
“Our findings do not only hold for those who have a particular genetic predisposition, but for anyone who chooses to drink, our study suggests that greater alcohol consumption leads to higher risk of dementia.”