While some research has suggested that light drinking may do the aging brain good, a new study finds that older adults who drink moderately may be no more or no less likely than abstainers to develop severe cognitive impairment.

The findings, from a study of nearly 3,900 Spanish adults, add to a conflicting body of research into whether moderate drinking is related to a lower risk of developing dementia.

A number of past studies have pointed to a potential protective effect. However, the researchers on the current work speculate that this may be because many of those studies lumped lifelong non-drinkers and former drinkers into one group.

This is an issue because at least some former drinkers may have given up alcohol due to health problems, explained lead researcher Dr. Elena Lobo Escolar of the University of Zaragoza in Spain.

So it’s possible that the inclusion of such individuals in a study’s “abstainer” group helps boost the average risk of cognitive decline.

For this latest study, published in the American Journal of Epidemiology, Lobo Escolar and her colleagues followed 3,888 initially dementia-free adults age 55 and older for 4.5 years.

They found that participants’ self-reported drinking habits at the outset showed no clear relationship with their likelihood of suffering serious cognitive decline over the study period.

Just over 13 percent of the study participants showed severe cognitive decline during the follow-up. There was no strong evidence that either light drinkers (those who had roughly one to six drinks per week) or moderate drinkers (about a drink or two a day) were less likely to see such a decline than those who had only occasionally drunk alcohol, if at all.

When the researchers factored in variables like study participants’ education levels, smoking habits, and health problems like high blood pressure, they found no statistically significant relationship between drinking habits and the odds of severe cognitive decline.

The researchers did find that former drinkers tended to have higher rates of physical disability and past smoking than either lifelong abstainers or current drinkers. And when abstainers and former drinkers were grouped together, the combined group showed a greater risk of severe cognitive decline than moderate drinkers.

This would tend to support the idea that including former drinkers in an abstainer group is problematic, Lobo Escolar told Reuters Health in an email.

However, a researcher not involved in the study said the findings do not negate those of previous work.

There are a number of differences in the methodology of the various studies on alcohol and cognitive decline that could help explain why they have arrived at different conclusions, according to Dr. Mary Ganguli of the University of Pittsburgh School of Medicine.

In a 2005 study published in Neurology, Ganguli and her colleagues found that among nearly 1,300 older adults they followed for up to 12 years, light-to-moderate drinkers generally showed a slower rate of decline on standard cognitive tests. The difference was greater when the researchers compared current moderate drinkers and former drinkers, but was still apparent in a comparison of current drinkers and lifelong abstainers.

That study and the current one had several key differences, Ganguli noted in an interview.

For one, she said, they looked at two culturally different populations - one from Spain, one from Western Pennsylvania - whose particular drinking habits (such as their alcohol of choice) may have been dissimilar. The studies also followed participants for different lengths of time, and had different outcome measures: the current study looked at rates of severe cognitive decline, whereas Ganguli’s study looked at participants’ average annual rate of decline.

“I’m not saying either study is ‘right’ or ‘wrong,’” Ganguli said. “But it is not surprising that they would have different conclusions.”

All of the studies on the association between moderate drinking and cognitive decline are limited by the fact that they are observational - where researchers ask people about their drinking habits and then follow their changes in cognition over time.

Such studies can only point to a relationship (or lack thereof) between drinking habits and cognitive decline - and cannot prove cause-and-effect.

Studies known as randomized clinical trials provide the best evidence of cause-and-effect. But it is not feasible to do a study where some people are randomly assigned to drink moderately and others to abstain, Ganguli pointed out.

For now, the weight of the evidence from observational studies comes down in favor of there being a relationship between moderate drinking and a lower risk of cognitive decline compared with abstention, according to Ganguli.

Exactly why that link exists is uncertain, she noted; further animal research, she said, could shed more light on how different levels of alcohol consumption affect cognition.

Both Ganguli and Lobo Escolar said there is a need for more in-depth observational studies that ask people detailed questions about their drinking habits.

The “good news” from this study, Lobo Escolar said, is that moderate drinking was not linked to any increase in the risk of severe cognitive decline. So older adults who already drink in modest amounts should feel no need to quit.

SOURCE:  American Journal of Epidemiology, online August 10, 2010