Heavy Drinking 'Strongest' Modifiable Risk Factor for Dementia

February 20, 2018

A new study suggests heavy alcohol consumption is a major risk factor for all types of dementia, but particularly early-onset dementia.

The retrospective analysis involving 30 million people in France shows that those with a history of alcohol use disorders had a threefold increased risk for dementia and that over half those with early-onset dementia had a history of alcohol problems.

"Our results suggest that heavy drinking is the strongest potentially modifiable risk factor for dementia that we have ever seen," lead author, Michaël Schwarzinger, MD, Translational Health Economics Network, Paris, France, told Medscape Medical News.

Their data make a strong argument for lower consumption of alcohol generally, he added. "If people are consuming more than a couple of alcoholic drinks a day, they could be putting themselves at increased risk of dementia. Our results suggest that one of the best things you can do for your brain health is to cut down your alcohol intake."

The study is published online in Lancet Public Health on February 20.

In an accompanying Comment, Clive Ballard, MD, and Iain Lang, MD, University of Exeter Medical School, United Kingdom, say the study is "immensely important and highlights the potential of alcohol use disorders, and possibly alcohol consumption, as modifiable risk factors for dementia prevention."

"This study used a phenomenally large database, and the result showing that half the cases of early-onset dementia were associated with alcohol use disorders is truly staggering," Ballard told Medscape Medical News.

"This has flagged something that has long been neglected, so it is a very important contribution to our knowledge," he added. "It does suggest that heavy drinking increases the risk for dementia and could be a significant contributing factor to early-onset dementia. That is important to know as we can potentially do something about it." 

In the paper, the researchers call for screening and interventions for heavy drinking and treatment for alcohol use disorders to reduce the alcohol-attributable burden of dementia.

"In our view, this evidence is robust and we should move forward with clear public health messages about the relationship between both alcohol use disorders and alcohol consumption, respectively, and dementia," Ballard and Lang add. "We might want to consider the extent to which the growing prevalence of dementia worldwide might be curbed by reductions in population-level alcohol consumption."

Quite a lot of work has looked at the effects of light drinking, with several cohort studies suggesting health benefits, including a possible reduction in dementia. But there has been very little research on the effects of heavy drinking, Schwarzinger noted, "so we wanted to look at this."

For the study, they analyzed a database covering all hospital admissions in France. "We had data on around 30 million people over a 6-year period, including 80% of the French population more than 60 years of age," Schwarzinger reported.

The researchers used diagnostic codes on hospital records to identify patients with dementia and those who had a history of alcohol use disorders. They found over a million cases of dementia, after excluding people with diseases that can lead to rare types of dementia and those with early-life mental disorders that can increase or confound dementia diagnosis. There were also 945,000 people with alcohol use disorders.

Results showed a strong association between a history of alcohol problems and dementia. This was especially noticeable in early-onset dementia, with 57% of the 57,000 patients who had developed dementia under the age of 65 years having a history of alcohol use disorders (66% of men and 37% of women).

In an analysis of just those patients in whom the first record of dementia occurred in 2011-2013 and adjusted for other risk factors found in the medical records, the risk for dementia was three times greater if the patient had a history of alcohol use disorders. The hazard ratio was 3.36 for men and 3.34 for women.

Is There a J-shaped Curve?

"We have very little information on the effects of heavy drinking as these people don't generally participate in studies and if they do they frequently drop out," Schwarzinger explained. "So this is the first solid data we have on this issue."

But he pointed out that some small neuroimaging studies have shown a relationship between alcohol use and gray matter damage. "This association appears to be linear — the more alcohol is consumed the more gray matter damage — right down to very low levels."

Because the current study used diagnostic codes to identify people with alcohol use disorders, it doesn't give a level of alcohol consumption considered to be hazardous for dementia risk. 

"We don't know how much they were actually drinking, but usually anyone with an alcohol use disorder would be drinking more than 5 units of alcohol a day," he said.  

The World Health Organization defines chronic heavy drinking as consuming more than 60 g of pure alcohol a day for men (around six or more standard drinks per day on average) and more than 40 g per day for women (around four or more standard drinks per day), the study authors note.

"Cohort studies suggest a J-shaped curve for the alcohol and dementia relationship, with low and moderate levels of drinking possibly having a benefit, but our study shows a clear harmful effect of heavy levels of drinking," Schwarzinger said. "We don't know where the threshold is. We cannot discern that information from this study."

He himself is not convinced about a J-shaped curve. "Personally I doubt there is a J-curve for the relationship between alcohol and brain health — the suggestion of benefit with low alcohol consumption has been seen in cohort studies in healthy people, which can have many biases, and the neuroimaging studies show brain damage with even low doses of alcohol."   

Ballard added: "There is a fair amount of evidence that modest alcohol consumption may be protective against dementia, and this study now suggests strongly that heavy drinking is harmful.  We don't know the specifics and we need to do a lot more work to find where the threshold may be, but possibly one or two drinks a day could be protective while five or more could be harmful." 

He further pointed out that there were almost certainly confounding factors that could have contributed to the current results.

"People with alcohol use disorders often also have many other risk factors for dementia, such as depression, social isolation, and poor nutrition, that may not have shown up in this study," he said. "But having said that, the very high hazard ratio in this study is certainly a big push for further research on heavy drinking."

The study received no external funding. Schwarzinger is the founder and CEO of THEN (Paris, France), which received research grants from AbbVie, Gilead, Merck, and Novartis. The other authors have disclosed no relevant financial relationships. Ballard reports grants and personal fees from Acadia Pharmaceuticals and Lundbeck, and personal fees from Roche, Otusaka, Novartis, Eli Lilly, and Pfizer, outside the submitted work. Lang has disclosed no relevant financial relationships. Lang's contribution was supported by the National Institute for Health Research Collaboration for Leadership in Applied Health Research and Care South West Peninsula. 

Lancet Public Health. Published online February 20, 2018.  Full text, Editorial

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