On the one hand, a great deal of research suggests that moderate alcohol consumption may be good for the heart and may also help prevent strokes. But alcohol also may be toxic to brain cells, Helms said.

"There is no safe level of alcohol when it comes to loss of brain volume," she said. "If you are worried about cognitive function, you shouldn't drink anything."

Helms said she would not recommend that anyone start or stop drinking moderately for health reasons.

However, she said it is reasonable for people to base their drinking habits on individual risk.

For instance, a person with a family history of heart disease or stroke might want to drink moderately. But a person with a family history of dementia or Alzheimer's disease might want to avoid alcohol, she said.

"Too much is not good," Helms said. "Unfortunately, it's not clear what that point is for any person."

The effect can be especially pronounced for women. Their rate of brain volume decline was roughly 50 percent more than for men across the various drinking categories.

Women tend to be affected by alcohol more than men, because they metabolize and absorb it differently. As a result, they achieve higher levels of alcohol in their blood and become more impaired from the same amount consumed by men of the same body weight.

Heavy drinking among men and women is known to be bad for both the heart and the brain, said Bhupendra Khatri, director of the Center for Neurological Disorders at Aurora St. Luke's Medical Center in Milwaukee.

Some of that likely is due directly to the alcohol and some of it probably is caused by the poor nutrition often found in heavy drinkers, he said.

What is interesting about the study is that it showed for both women and men that alcohol consumption was associated with a linear decline in brain volume from light drinking to heavy drinking, he said.

"The more you drink, the more it (the brain) atrophies," said Bhupendra Khatri, director of the Center for Neurological Disorders at Aurora St. Luke's Medical Center in Milwaukee, who was not part of the study. "There is a fine balance in life. You need to look at your own risk factors."