People who have sworn off alcohol for decades or longer, run a higher risk of dementia late in life than moderate drinkers, according to a new study.
Long-term teetotallers were roughly 50 per cent more likely to suffer Alzheimer's or another form of neurodegenerative disease, scientists reported in the BMJ, a medical journal, on Wednesday.
With heavy drinking, however, dementia became even more prevalent, though for different reasons.
Unlike earlier research, the study did not find a link between abstinence and a shorter life expectancy, as compared to occasional drinkers.
The results were based on a review of medical records rather than the more scientifically rigorous clinical trials used to assess new drugs, and the number of cases examined was relatively small.
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But the startling results are robust, and should prompt government-funded trials to assess "the possible protective effect of light-to-moderate alcohol use on risk of dementia," commented Sevil Yasar, an associate professor at the John Hopkins School of Medicine who was not involved in the study.
At the same time, the study cautioned, the findings "should not motivate people who do not drink to start drinking given the known detrimental effects of alcohol consumption for mortality, neuropsychiatric disorders, cirrhosis of the liver and cancer."
Worldwide, about seven percent of people over 65 suffer from some form of dementia, a percentage that rises to 40 percent above the age of 85. The number of sufferers is expected to triple by 2050.
The research, led by Severine Sabia at the French National Institute of Health and Medical Research, also found that -- among moderate drinkers -- wine consumption correlated with a lower risk of dementia than beer or spirits, such as whiskey, gin or vodka.
"Light-to-moderate" drinking was defined, during middle age, as one-to-14 drinks per week, corresponding to the maximum limit recommended for both men and women in Britain.
The 14-drink-per-week maximum -- similar to guidelines in other countries -- is the equivalent of six medium (175-millilitre) glasses of wine at 13 percent alcohol, six pints of four-percent beer, or 14 25-ml shots of 40-degree spirits.
The study was not set up to explain why non-drinkers might be more prone to cognitive decline, but the findings offered possible clues.
"Some of the excess risk of dementia in abstainers was explained by greater risk of cardiometric disease," such as stroke, coronary heart disease and diabetes, Sabia and her team concluded.
Non-drinkers canvassed were more likely to be burdened with lifestyle diseases, but the link with dementia held true even after these health problems were taken into account, they reported.
Because the study only tracked alcohol consumption starting in midlife, it is also possible that a prior history of heavy drinking might have contributed to dementia many decades later, one expert not involved in the study cautioned.
"Future research will need to examine drinking habits across a whole lifetime, and this will help to shed more light on the relationship between alcohol and dementia," Sara Imarisio, head of research at Alzheimer's Research UK, told the Science Media Centre.
In the case of wine, earlier studies have suggested that so-called polyphenolic compounds may offer some protection to neural networks and blood vessels, but such findings remain controversial.
The findings are based on health records -- part of the Whitehall II study on long-term health -- for more than 9,000 British civil servants who were 35 to 55 years old in 1985.
Alcohol intake of participants was monitored regularly for two decades, and hospital records were examined for signs of heart and alcohol-related disease.
A total of nearly 400 dementia cases -- with onset occurring, on average, at age 76 -- were reported.
The study also confirmed that heavy drinking is strongly linked to dementia, with a 17-percent increase in risk for each additional seven drinks per week.
Chronic heavy drinking has been clearly established as a major risk factor for all types of dementia, especially early onset of the disease.