It’s not clear why even modest amounts of alcohol may shrink the brain, although alcohol is “known to dehydrate tissues, and constant dehydration can have negative effects on any sensitive tissue,” says Paul.

“We always knew that alcohol at higher dosages results in shrinking of the brain and cognitive deficit,” says Petros Levounis, MD, director of the Addiction Institute of New York at St. Luke’s – Roosevelt Hospital Center, who was not involved in the study. ”What is new with this article is that it shows brain shrinking at lower doses of alcohol.”

However, the study did not demonstrate that the smaller brain volume actually impaired memory or mental function, notes James Garbutt, MD, professor of psychiatry at the University of North Carolina at Chapel Hill.

And the differences between brain volumes in drinkers and nondrinkers were quite small—less than 1.5% between abstainers and heavy drinkers.

“We’re talking very small differences here,” says Dr. Garbutt, who was not involved in the study. “We’re not seeing 10%–20% shrinkage.”

However, he says, reduction in brain mass is an interesting finding. “But we have a long way to go to figure out the implications of it.”

(PHOTO: FOTOLIA)

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