Too much -- or too little -- alcohol consumption in midlife may be linked to an increased risk for dementia later in life, researchers reported.

In a large prospective study of over 9,000 individuals, abstention from alcohol consumption in midlife was tied to a significantly higher risk for dementia over a 23-year follow-up period compared with those who drank between 1 to 14 units of alcohol per week (HR 1.47, 95% CI 1.15-1.89), according to lead author Séverine Sabia, research associate at the Université Paris-Saclay in France, and colleagues.

However, those who consumed over 14 units of alcohol per week also saw an increased risk for dementia, with every 7-unit increase in alcohol tied to a 17% increase in dementia risk (95% CI 4%-32%), they wrote in the BMJ.

Measures of liquor, glasses of wine, and pints of beer were converted to units of alcohol consumed per week, the authors noted.

Between midlife -- 35 to 55 years of age -- and early old age, certain drinking patterns and trajectories were also found to be associated with an increased risk for dementia compared with people who steadily kept their alcohol intake between 1 to 14 units:

Long-term abstinence: HR 1.74 (95% CI 1.31-2.30)

Long-term high consumption (>14 units/week): HR 1.40 (95% CI 1.02-1.93)

Decrease in consumption: HR 1.55 (95% CI 1.08-2.22)

Other factors tied to heavy drinking were also associated with a much higher risk for dementia later in life. Individuals who had a CAGE score over 2, which measures alcohol dependence, saw over twice the rate of dementia (HR 2.19, 95% CI 1.29-3.71). Similarly, those who had experienced an alcohol-related hospital admission had the highest associated risk for dementia later in life (HR 4.28, 95% CI 2.72-6.73) -- an outcome which the authors state is "supporting findings on the neurotoxic effects of alcohol consumption >14 units/week."

Interestingly, the researchers found that the link between alcohol abstention and dementia may be, at least in part, explained by cardiometabolic disease. Specifically, those who abstained from alcohol and did not have cardiometabolic disease (HR 1.33, 95% CI 0.88-2.02) had a lower rate of dementia compared with the rest of the study population (1.47, 95% CI 1.15-1.89).

Although some prior studies have also found a positive association between alcohol abstention and an increased risk for dementia, the researchers highlighted how this "finding [is] subject to much debate."

"Our analyses using repeat data on alcohol consumption across midlife suggest that former drinking might not explain the excess dementia risk in abstainers, although we cannot exclude the possibility that those who report alcohol abstinence in midlife were heavy drinkers in young adulthood or misreported their alcohol consumption," they explained, and highlighted how their analysis was adjusted to account for several sociodemographic and health-related factors.

The analysis included individuals from the Whitehall II study, who were employees in civil service offices in London. Alcohol consumption was measured via several questionnaires administered between 1985 to 2016, while dementia diagnosis was collected from electronic health records. Over the study period, nearly 400 individuals developed dementia. Despite the large sample size, the researchers highlighted the observational nature of the design as a limitation to the study.

This was echoed by accompanying editorial author, Sevil Yasar, MD, PhD, of Johns Hopkins School of Medicine in Baltimore, who stated that although this study was able to fill gaps in the current literature, "we should remain cautious and not change current recommendations on alcohol use based solely on epidemiological studies." Yasar instead suggested another confirmatory study -- ideally a randomized clinical trial -- specifically aimed at assessing any potential protective effects of light-to-moderate alcohol consumption.

As for now, the research group recommended that governing bodies look at their individual guideline recommendations for alcohol consumption, noting how some countries have a higher threshold than 14 units per week to define excessive consumption. "The present study encourages the use of a lower threshold of alcohol consumption in such guidelines, applicable over the adult life course, in order to promote cognitive health," they suggested.