White matter is important for relaying messages across the brain, Karoly said, "so damage to white matter could have a whole host of negative implications as far as cognitive processes such as memory, attention and self-regulation." The subjects didn't take tests to assess any of those mental abilities, however.
The people in the study who appeared to exercise the most reported that they got two or more hours of exercise per week. But it's not clear what kind of exercise they got or how accurate their recollections about exercise were.
Oddly, the participants in the study who exercised the most also drank the most -- nearly 1.75 drinks a day, on average. Those who exercised the least drank an average of less than 1.4 drinks a day.
Although the study showed an association between exercise and brain health, it did not prove a cause-and-effect link.
Garbutt said it's difficult to find definitive conclusions in the research. "I would view this as a very early, preliminary study that may highlight some areas for future research but doesn't provide much in the way of a solid finding to communicate to the public," he said.
Garbutt cautioned that anyone who drinks heavily or suffers from alcoholism "should get a good medical evaluation before undertaking aerobic exercise. Alcohol can affect heart rhythms, bone strength and the liver and pancreas, and one shouldn't start major exercise without knowing if there are risks such as heart problems."
But if a physician says it's OK, "exercise is good and might even help the brain," he said.
The study was published online April 16 and will appear in the September issue of the journal Alcoholism: Clinical & Experimental Research.
For more about alcoholism, try the U.S. National Library of Medicine.
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