(Reuters Health) - Heavy drinkers may be more likely than other adults to develop dementia, especially in middle age, a French study suggests.

For the study, researchers examined data from 2008-2013 on more than 31 million French hospital patients, including more than 1 million who were diagnosed with dementia. About 5 percent of the dementia patients had so-called early onset dementia that started before age 65, and most of these cases were alcohol-related, the study found.

“Chronic heavy drinking was the most important modifiable risk factor for dementia onset in both genders and remained so after controlling for all known risk factors for dementia onset,” said lead study author Dr. Michael Schwarzinger, chief executive officer of Translational Health Economics Network and a researcher at INSERM–Universite Paris Diderot, Sorbonne Paris Cite in France.

Surprisingly, heavy drinkers who got sober didn’t have a lower dementia risk than their peers who remained problem drinkers,” Schwarzinger said by email .

“This finding supports that chronic heavy drinking leads to irreversible brain damage,” Schwarzinger added.

While some previous research suggests that alcohol may lead to cognitive impairments including a risk of dementia, other studies have linked light or moderate alcohol use to a healthier brain, researchers note in the Lancet Public Health.

Globally, an estimated 3.3 million people a year die as a result of alcohol misuse, accounting for about 6 percent of all deaths, according to the World Health Organization (WHO).

The WHO defines chronic heavy drinking as more than 60 grams of pure alcohol, or at least 6 drinks, for men and more than 40 grams, or at least 4 drinks, for women.

During the study period, 945,512 people were diagnosed with alcohol use disorders. Most of these cases were alcohol dependency.

Overall, about 3 percent of the dementia cases were attributable to alcohol-related brain damage, and other alcohol use disorders were recorded in almost 5 percent of dementia cases.

With early onset dementia cases, however, the connection to alcohol appeared stronger. About 39 percent of these cases were attributable to alcohol-related brain damage, and another 18 percent were tied to other alcohol use disorders.

Alcohol use disorders were associated with three times the risk of dementia and twice the risk of early onset cases, the study found. Excluding alcohol-related brain damage, alcohol use disorders were still associated with a two times greater risk of vascular and other dementias.

Alcohol use disorders were also associated with all other independent risk factors for dementia, such as tobacco smoking, high blood pressure, diabetes, lower education, depression, and hearing loss.

The study wasn’t a controlled experiment designed to prove whether or how drinking might cause dementia or cause cognitive problems to develop in middle age.

Another limitation is that researchers used hospital administrative records to identify dementia cases, and it’s possible the condition might have been recorded when patients had multiple medical problems, researchers note. Similarly, alcohol use disorders were identified through records of rehabilitation programs, which might not include all individuals with drinking problems.

Because the study focused on heavy drinkers, it also doesn’t provide insight into how much a drink or two a day might be linked to an increased risk of dementia, if at all.

Even so, the findings add to the evidence that heavy drinking can lead to cognitive problems, said Clive Ballard co-author of an accompanying editorial and Dean of the medical school at the University of Exeter in the U.K.

“Seven drinks per day in men and five drinks per day in women are harmful to the brain,” Ballard said by email. “But levels of recommended alcohol consumption are already lower than this, and this provides additional reinforcement of those recommendations.”

SOURCE: bit.ly/2FpdtLp Lancet Public Health, online February 20, 2018.