Adults in middle age who drink the equivalent of seven glasses of wine or more per week have a higher risk of developing dementia in their senior years than light drinkers—but the same is also true for those who abstain from alcohol entirely, according to a study published in BMJ.
For the study, researchers in the United Kingdom followed 9,087 adult participants between the ages of 35 and 55 and assessed the participants' alcohol consumption through five different assessments between 1985 and 2004. The researchers used medical records of alcohol-related diseases between 1991 and 2017 and questionnaire data to assess problem drinking.
The researchers measured alcohol consumption in units of alcohol—a UK measurement in which one unit contains 8 grams of pure alcohol. By that measure, a six-ounce glass of wine contains about two units of alcohol, a half imperial pint of 9.6 ounces of beer contains one to three units of alcohol, and one ounce of spirits is equivalent to one unit of alcohol.
'Heavy drinkers' and abstainers at higher risk of dementia
Over an average of 23 years, 397 participants developed dementia, at an average age of 76.
Overall, the researchers found dementia risk was lowest among those who consistently drank one to 14 units of alcohol weekly.
Participants who abstained from alcohol entirely in middle age were 47% more likely to develop dementia than "moderate or occasional drinkers," who the researchers defined as having one to 14 units of alcohol per week. That figure rose to 74% among those who consistently abstained from alcohol during and after middle age.
Among heavy drinkers, whom the researchers defined as having more than 14 units of alcohol per week, the study showed each seven-unit increase in weekly alcohol consumption increased dementia risk by 17%.
The participants who continued to drink 14 units per week after middle age were 40% more likely than moderate or occasional drinkers to develop dementia. Participants who reduced their drinking habits later in life were still 55% more likely to develop dementia than the consistent moderate or occasional drinkers.
Why are alcohol abstainers at greater dementia risk?
The study was not designed to test how alcohol consumption affected dementia risk, but the authors offered some suggestions. Lead author of the study, Severine Sabia from Paris-Saclay University and University College London, said the increased risk of dementia in people who drink more than 14 units per week could be a result of brain toxicity and poor nutrition from alcohol consumption.
As for the participants who didn't drink, abstinence may be connected to dementia among those who quit drinking because of alcohol misuse, Sabia said, which could contribute to the heightened dementia risk.
"Regarding the [abstainers], several other studies have suggested that very modest alcohol consumption may be protective from cardiovascular disease, and this study further supports that idea," Rebecca Gottesman from the Johns Hopkins University School of Medicine said. She added, "But I don't think we understand enough about how it might do so."
Importantly, Sabia said these findings "should not motivate people who do not drink to start drinking alcohol due to the adverse effects of alcohol on mortality, cirrhosis of the liver and cancer" (Rapaport, Reuters, 9/26; Sabia et al., BMJ, 8/1 ).
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