Heavy drinking can increase risk of early-onset dementia, according to the largest study of its kind ever conducted.

The study looked over one million adults diagnosed with dementia in France.The research looked specifically at the effect of alcohol use disorders, and included people who had been diagnosed with mental and behavioural disorders or chronic diseases that were attributable to chronic harmful use of alcohol. Of the 57,000 cases of early-onset dementia (before the age of 65), the majority (57%) were related to chronic heavy drinking.

The World Health Organization (WHO) defines chronic heavy drinking as consuming more than 60 grams pure alcohol on average per day for men and 40 grams per day for women. As a result of the strong association found in this study, the authors suggest that screening, brief interventions for heavy drinking, and treatment for alcohol use disorders should be implemented to reduce the alcohol-attributable burden of dementia.

"The findings indicate that heavy drinking and alcohol use disorders are the most important risk factors for dementia, and especially important for those types of dementia which start before age 65, and which lead to premature deaths," says study co-author Dr. Jürgen Rehm. "Alcohol-induced brain damage and dementia are preventable, and known-effective preventive and policy measures can make a dent into premature dementia deaths."

Dr. Rehm points out that on average, alcohol use disorders shorten life expectancy by more than 20 years, and dementia is one of the leading causes of death for these people. For early-onset dementia, there was a significant gender split. While the overall majority of dementia patients were women, almost two-thirds of all early-onset dementia patients (64.9%) were men.

Alcohol use disorders were also associated with all other independent risk factors for dementia onset, such as tobacco smoking, high blood pressure, diabetes, lower education, depression, and hearing loss, among modifiable risk factors. It suggests that alcohol use disorders may contribute in many ways to the risk of dementia. "As a geriatric psychiatrist, I frequently see the effects of alcohol use disorder on dementia, when unfortunately alcohol treatment interventions may be too late to improve cognition," says CAMH Vice-President of Research Dr. Bruce Pollock. "Screening for and reduction of problem drinking, and treatment for alcohol use disorders need to start much earlier in primary care."

The authors also noted that only the most severe cases of alcohol use disorder - ones involving hospitalization - were included in the study. This could mean that, because of ongoing stigma regarding the reporting of alcohol-use disorders, the association between chronic heavy drinking and dementia may be even stronger. The findings have been published in The Lancet Public Health journal.