August 26, 2011 — Light to moderate drinking seems to reduce the risk for dementia and cognitive decline, according to a new study published in the August issue of Neuropsychiatric Disease and Treatment.
A meta-analysis of 143 studies on the effects of alcohol on the brain showed that moderate drinking, defined as no more than 2 drinks a day for a man and no more than 1 drink a day for a woman, reduced the risk for Alzheimer's disease and other forms of dementia by 23%.
"It doesn't seem to matter if it's beer, wine, or spirits, as long as the drinking was moderate," Edward J. Neafsey, PhD, from the Department of Molecular Pharmacology and Therapeutics at Loyola University Medical Center, Maywood, Illinois, told Medscape Medical News.
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Dr. Edward J. Neafsey
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Dr. Neafsey and coauthor Michael A. Collins, PhD, became interested in seeing whether alcohol might be protective of human brains after their experiments showed that rat brains exposed to low doses of alcohol for a few days demonstrated resiliency when subsequently treated with a toxin.
"If the rat brain slices were treated for 5 or 6 days with low alcohol and then the toxin was administered, there was hardly any damage, whereas if they didn't get the pretreatment with alcohol, there was significant damage. This led us to ask if there was anything in the human literature that would fit with this protective effect of alcohol," Dr. Neafsey explained.
The researchers reviewed studies dating from 1977 up to the present. The studies fell into 2 categories: those that provided ratios of risk between drinkers and nondrinkers (n = 74) and those that rated cognition in drinkers as "better," "no different," or "worse" than cognition in nondrinkers (n = 69).
Heavy Drinking a Different Story
Light to moderate drinking conferred a similar benefit, but heavy drinking (more than 3 - 5 drinks/day) was associated with a nonsignificantly higher risk for dementia and cognitive impairment.
Most of the studies did not distinguish between the different types of alcohol, but in a few studies, wine appeared to be more beneficial than beer or spirits. "It really seemed to be that alcohol per se was protective, not the type, because the few studies that did make the distinction reported no difference among the effects of the different types of alcohol," Dr. Neafsey said.
The protective effect of moderate drinking held after adjusting for age, education, sex, and smoking.
A number of explanations for the protective effect of moderate alcohol have been proposed. Some dementias are related to cardiovascular system problems, such as atherosclerosis, and alcohol may be protective because it raises the level of high-density lipoprotein (the good) cholesterol and might improve blood flow in the brain.
One theory that Dr. Neafsey and Dr. Collins are working on now holds that alcohol acts as a mild stressor for brain cells and "preconditions" them, making them better able to ward off stress.
"Alcohol doesn't kill the brain cells, but it's a slight stress. When the cells are exposed they increase levels of various protective compounds, so...they are prepared when something more stressful that might kill or damage them comes along. The theory is called 'preconditioning,' where a mild stress given a few days before a severe stress causes a significant protection."
Understanding the mechanism of alcohol's protective effect could lead to a treatment to prevent cognitive impairment and dementias, Dr. Neafsey said.
"Whether it's treatment with a pill or a lifestyle change, if we could understand the mechanism, it would improve our ability to deal with these illnesses," he said.
Novel Approach
Medscape Medical News asked Anton P. Porsteinsson, MD, the William B. and Sheila Konar professor of psychiatry at the University of Rochester School of Medicine, New York, to comment on this study.
"This is a well-done meta analysis. The findings are consistent with other meta analyses that have been done. Am I tremendously surprised at the findings? No, because they are looking at the same pool of studies," Dr. Porsteinsson said.
"The fact that they approach it in slightly different ways and yet find similar outcomes makes me confident that this is what the data are actually signaling to us: that very modest alcohol consumption is protective," he said.
The next step is to figure out how moderate alcohol consumption exerts its protective effect.
"Is it some direct effect of the alcohol on the brain? Are people who consume moderate amounts of alcohol different in some way, in their diet, or their level of exercise? Are low concentrations of alcohol neuroprotective? Is it through some metabolic impact?" Dr. Porsteinsson said.
Also interesting was that alcohol appeared to protect against all types of dementia, he said.
"This makes it less likely to have a direct effect on beta amyloid or tau, but more of a global effect. It is an interesting review. They made it a pleasure to read."
The study was supported by the National Institutes of Health. Dr. Neafsey, Dr. Collins, and Dr. Porsteinsson have disclosed no relevant financial relationships.
Neuropsychiatric Dis Treat. 2011;7:465-484. Abstract
