Small amounts of alcohol raise levels of high-density lipoprotein -- the beneficial form of cholesterol -- in women but not in men, according to a new study by Oregon researchers.

Scientists at the Oregon Health Sciences University in Portland examined the effects of consuming no more than one drink of alcohol per day in more than 300 men and women. Blood cholesterol levels were measured at the start of the study and one year later.

The researchers found that consuming one ounce of alcohol per day or less had no effect on blood levels of HDL in the 170 men participating in the study. But for women, drinking small amounts of alcohol daily helped raise levels of protective HDL. Studies show that the higher the HDL level, the lower the risk of heart disease.

All the women in the study had HDL levels above the ideal level of 50 milligrams. But those who drank one ounce of hard liquor per day -- or the equivalent amount of alcohol found in one 12-ounce beer or one 4-ounce glass of wine -- averaged the best HDL levels: 63 milligrams per deciliter.

By comparison, women who drank five to 30 drinks per month -- less than one per day -- averaged HDL levels of 58 milligrams, a small but significantly lower level, said Sonja Connor, a co-author of the study. The lowest HDL levels were found in women who consumed four or fewer drinks per month. HDL levels in this group averaged 53 mg.

The findings suggest that small amounts of alcohol have a more significant effect on women's blood cholesterol levels than on men's, the researchers noted in the January issue of Circulation, a journal published by the American Heart Association. They say they don't know why the disparity exists.

But Connor also cautioned that considering other potentially harmful effects of alcohol on health, the results don't give women a license to drink large amounts of alcohol.