June 15, 2005
Heavy Drinking Has Lasting Impact on Memory
Mouse study finds heavy alcohol use has lasting impact on learning and memory
Heavy drinking doesn't damage just your liver; it can also do serious harm to your brain, a new study of mice suggests.While past studies have shown that alcohol can impair memory and learning ability, the new research finds that such damage can occur in a shorter period of time than was previously thought.
Reporting in the June issue of Alcoholism: Clinical and Experimental Research, researchers found that after as few as eight weeks of heavy drinking, mice showed significant, and apparently permanent, deficits in memory and learning.
"Heavy drinking causes lasting effects, even when you stop," said study co-author Susan Farr, an associate professor of medicine at St. Louis University School of Medicine.
Mice that were exposed to alcohol daily for eight weeks were "twice as impaired" as normal mice when it came to tasks requiring learning or memory, said Farr. And those changes appeared to affect all types of learning and memory.
"We did a series of tests and found global impaired learning and memory. We found deficits in every type of task we tested the mice in," said Farr. After 12 weeks with no alcohol, the mice still showed impairment.
For the study, Farr and her colleagues fed 8-week-old male mice a diet of either 20 percent alcohol or sugar water for a period of four weeks or eight weeks, followed by a three-week period of withdrawal from alcohol before testing. Each group had an average of 10 mice.
The amount of alcohol given to the mice would equal about six to eight beers or one bottle of wine daily for a human. The eight-week time period for mice is equivalent to about six years for a human, said Farr.
After the withdrawal period, the researchers administered a series of tests designed to measure the rodents' memory and learning ability.
"Mice that were exposed for four weeks weren't impaired in learning and memory, but the eight-week mice were," Farr said.
The researchers retested the mice after an additional 12 weeks with no alcohol to see if their memory or learning improved, but they didn't.
Farr said the researchers don't know exactly how alcohol causes deficits in learning and memory, but suspect that the drug causes damaging neurochemical changes in the brain.
But one expert said the study findings may not translate easily to humans.
"The authors suggest that a heavy drinking load, as stipulated in their equivalency for humans, would compromise cognition and thinking. The equivalency between mouse metabolism and human metabolism, however, is inevitably somewhat speculative, and conclusions from the study regarding people's drinking should be drawn only very carefully," said Dr. Marc Galanter, director of the division of alcoholism and drug abuse at New York University School of Medicine's department of psychiatry.
"Nonetheless, heavy drinking in both adults and adolescents is unquestionably unhealthful," he added.
Farr agreed. She also said the average drinker doesn't need to be concerned about the study results. "This has to be constant drinking. These deficits would be in someone that drinks a lot every day."
"Everything in moderation," Farr added. "There have been some studies that show a drink or two a day has a positive effect."
The National Institute on Alcohol Abuse and Alcoholism offers more information on how drinking affects your brain.