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Thomas S. May, M.A.Medical Writer |
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Does Alcohol Kill Brain Cells? Maybe Not
Thomas S. May, Medical Writer
Introduction Studies comparing the brains of alcoholic and nonalcoholic adults consistently show that chronic alcohol abuse can lead to a significant reduction in brain size. (See sidebar.) We also know that alcohol--when ingested by a pregnant woman--can cause irreversible damage to the developing brain, resulting in fetal alcohol syndrome. But is it true that people lose a large number of their brain cells every time they get drunk, or is this just another unfounded myth--an "old wives' tale"?
"There is presently no strong evidence to conclude that any given session of alcohol consumption causes brain cells to die," says Walter Hunt, PhD, a senior science advisor at the National Institute on Alcohol Abuse and Alcoholism (NIAAA).
But some people who drink large amounts of alcohol for a long period of time may be susceptible to brain damage, according to Dr. Hunt. "Those who go through periods of intoxication and withdrawal over and over again are especially vulnerable. The evidence suggests that most of the brain damage actually occurs during withdrawal rather than during intoxication," he says. Alcohol affects a variety of different neurotransmitters (chemicals that help transmit messages between brain cells), and the overall effect is the inhibition or reduction of brain cell activity. When alcohol is removed, the affected nerve cells are overstimulated, and this may result in some of those cells being damaged in the process, Dr. Hunt explains.
Not in the Cerebellum One area of the brain that has been studied extensively in relation to alcohol intake is the cerebellum, which is the control center for movement, balance, and coordination. Alcohol has a profound effect on the cerebellum, and that is why people who had too much to drink often lose their balance and tend to stagger and stumble. Roberta Pentney, PhD, is a professor of anatomy and cell biology at the State University of New York at Buffalo, and she has studied the effects of chronic alcohol intake on certain brain cells called "Purkinje neurons" in the cerebellum of rats for almost 20 years. Alcohol affects the way these neurons operate, and it also causes some structural changes in these nerve cells, according to Dr. Pentney. "My studies of the effects of alcohol on cerebellar neurons in rats that have consumed alcohol during the entire second half of their life span have shown that there are changes in the dendritic structures of these neurons," she says. (Dendrites are branchlike appendages through which neurons receive messages from adjoining nerve cells.) "These changes appear to be reversible, in that the dendritic segments that were lost reappear. There is some evidence, however, that they do not reappear at exactly the same place. So the repaired dendritic structures are not identical to the original dendritic structures," Dr. Pentney explains. Pentney says that although long-term alcohol exposure appears to cause some changes in some areas of the brain, her work indicates that alcohol does not actually kill brain cells. At the same time, she is careful to point out that it is "rather risky to extrapolate" these results to humans. However, some other studies performed on humans during the past few years also indicate that chronic alcohol intake does not, in itself, lead to brain cell death. For example, Clive Harper, MD, and his colleagues at the University of Sydney, Australia, conducted a study that analyzed the brains of people who died after having abused alcohol for several decades. The researchers found some cell loss in the cerebellum of the alcoholic subjects who were also deficient in thiamine (vitamin B1). But they found no cell loss in the brains of chronic alcohol abusers who did not have thiamine deficiency. As a result, the scientists concluded that long-term, excessive alcohol intake does not, in itself, cause brain damage in humans--at least not in the cerebellum. However, thiamine deficiency is a very common side effect of chronic alcohol abuse, and this may explain why the brains of many alcoholics are smaller than normal.
Of Rats and Humans Fulton Crews, MD, PhD, is a professor of pharmacology and psychiatry, and he is the director of the Bowles Center for Alcohol Studies at the University of North Carolina (UNC) at Chapel Hill. He claims that even a single, prolonged episode of binge drinking can cause long-term--and possibly permanent--brain damage, especially in adolescents. Dr. Crews bases his argument on experiments performed recently by his group at UNC. In one of the experiments, the investigators observed some brain cell destruction in rats (especially in juvenile rats) that had been given 9-10 grams per kilogram of body weight per day alcohol for 4 days in a row.2 This amount is equivalent to roughly 800 grams of alcohol per day or about 3.2 kilograms of alcohol (260 regular drinks!) ingested over 4 days by an average-sized man. After 4 days of injecting them with such a large amount of alcohol, the investigators removed the experimental animals' brains, and they were able to demonstrate that some neurons have, in fact, died in the process. Obviously, experiments like this cannot be performed on humans. Therefore, scientists can only guess what kind of damage, if any, may occur when people consume excessive amounts of alcohol. Nevertheless, the fact that brain cell death could be demonstrated in animals exposed to very large amounts of alcohol in a relatively short period of time indicates that some cell loss probably does occur when people become drunk, according to Dr. Crews.
Thomas S. May is a medical
journalist based in Toronto, Ontario, Canada. He has a master's degree in
psychology from Simon Fraser University in Burnaby, British Columbia. Source: Medscape Health
Reprinted from Medscape Health for Consumers.
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