A large-scale observational study of over one million adults has confidently linked chronic heavy alcohol consumption with early-onset dementia. The strong association confirms several recent similar studies examining the damaging effects of alcohol on the brain.

The massive study examined the records of all adult patients admitted to hospitals in metropolitan France over a five-year period. Some 1.1 million subjects were found to have been diagnosed with dementia in that time and over 57,000 of those cases were classified as early-onset, meaning they were displaying symptoms at ages younger than 65 years. Strikingly, 57 percent of those early-onset dementia cases were associated with an alcohol-use disorder defined as chronic alcohol use or alcohol dependence.

"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 Jürgen Rehm.

The study comes just weeks after another research paper suggested moderate levels of alcohol could be good for the brain. While it may superficially seem like this is a classic case of ping-pong science news, where one day something is good for you and the next day it isn't, these two studies are actually incredibly complimentary.

The previous research uncovered that while very low-doses of alcohol can help flush the brain of toxins, excessive amounts of alcohol result in exactly the opposite effect. It is this mechanism that could possibly explain the strong observational association found in this new research. Another recent study uncovered a mechanism demonstrating how alcohol can permanently damage DNA in stem cells, increasing a person's risk of cancer.

Of course, despite the large cohort in this newly published research, it is still an associational study, meaning no explicit cause-and-effect relationship can be truly proven. The limitations of the study are worth keeping in mind as it does not suggest moderate drinking causes dementia and the cohort utilized were limited to those admitted to a hospital due to heavy alcohol use.

Tara Spires-Jones, a dementia researcher from the University of Edinburgh who was not affiliated with this study, suggests that the biggest takeaway from this work is that excessive alcohol consumption is incredibly damaging to a body.

"This finding is not too surprising since it is well known that excessive alcohol use can cause alcohol-related dementia," says Spires-Jones. "There are other studies that indicate that moderate amounts of red wine as part of a healthy diet may protect against developing dementia, however it is crystal clear that alcohol abuse is bad for your brain."

The new study was published in the journal Lancet Public Health.