By Lisa Rapaport

(Reuters Health) – Middle-aged adults who avoid alcohol altogether, and those who consume the equivalent of seven glasses of wine or more a week are both more likely than light drinkers to develop dementia in their later years, a long-term study suggests.

With heavy drinking, the increased risk of dementia may be directly caused by nutritional deficits and the toxic effects of alcohol in the brain, and indirectly caused by disorders that are common among heavy drinkers like diabetes, high blood pressure and stroke, said lead study author Severine Sabia of Paris-Saclay University in France and University College London in the UK.

Abstinence is also associated with a higher likelihood of having heart disease or diabetes, which explains part of the increased dementia risk for teetotalers, the study found. Abstinence may also be tied to dementia in people who stopped drinking due to misuse or addiction, Sabia said by email.

“Findings on abstainers 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,” Sabia noted. “In addition, given the detrimental effect of alcohol for several health outcomes, people who drink in an excessive manner should be encouraged to reduce their alcohol consumption.”

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).

For the study, Sabia’s team used a standard UK measurement, units of alcohol, where each unit contains 8 grams of pure alcohol. So a medium glass of wine (175 ml or about 6 oz) would contain about 2 units of alcohol, half an imperial pint (9.6 fluid ounces) of beer would contain 1 to 3 units of alcohol, depending on its strength, and a standard measure (25 ml or about 1 oz) of spirits would equal one unit of alcohol.

The researchers followed 9,087 adults participating in a long-term study in the UK for an average of 23 years with five assessments of alcohol consumption between 1985 and 2004. They also looked at data from questionnaires to assess problem drinking and at medical records of alcohol-related diseases between 1991 and 2017.

During the study, 397 people developed dementia, at an average age of 76, the study team reports in The BMJ.

Compared with people who had 1 to 14 units of alcohol a week in middle age, teetotalers were 47 percent more likely to develop dementia.

Among people having more than 14 units a week, each 7-unit increase in alcohol consumption was associated with a 17 percent increase in the risk of dementia.

The study also looked at how any shifts in drinking patterns after middle age might impact the risk of dementia, and they found the lowest risk among people who consistently consumed 1 to 14 units of alcohol a week.

Compared to these consistent light-to-moderate drinkers, people who maintained long-term abstinence were 74 percent more likely to develop dementia. Those who kept up a heavy drinking habit were 40 percent more likely to develop dementia. When people cut back after middle age, they were 55 percent more likely than the consistent occasional or moderate drinkers to develop dementia.

The study wasn’t designed to prove whether or how drinking habits might impact the development of dementia.

However, the results suggest that guidelines in many countries that set the bar for problem drinking at much higher than 14 units a week may need to be revised to account for the potential dementia risk, the study authors conclude.

“The study provides important support for another downside to heavy alcohol use,” said Dr. Rebecca Gottesman of Johns Hopkins University School of Medicine in Baltimore.

“Regarding the other end of the spectrum, several other studies have suggested that very modest alcohol consumption may be protective from cardiovascular disease, and this study further supports that idea, but I don’t think we understand enough about how it might do so,” Gottesman, who wasn’t involved in the study, said by email.

SOURCE: The BMJ, online August 1, 2018.