For men, the more they drank, the lower the risk. One drink a week lowered the risk by about 7 percent, two to four drinks by 22 percent and five or six drinks a week by 29 percent. Those who drank every day had a 41 percent lower risk of heart disease than those who did not drink at all. Even among men who had up to 35 drinks per week, the protection persisted.

With women, the trend was different. One drink a week lowered the risk by 36 percent, but daily drinking lowered it by 35 percent. In other words, for women, alcohol consumption had a significant protective effect, but the frequency of drinking had none.

Dr. Morten Gronbaek of the Danish National Institute of Public Health, the study's senior author, said he would not hesitate to recommend a drink a day to certain patients. "If I were talking to a patient, about 50 with a high coronary risk profile, who I knew wasn't at risk for alcohol abuse, and who didn't drink at all, I wouldn't hesitate to tell him that a glass of wine a day might be a good idea," he said. "But people who are light drinkers should certainly not be advised to drink more."

The researchers also stressed that their data said nothing about binge drinking or about the number of drinks per occasion, and Dr. Gronbaek said that drinking was not a substitute for exercise or good diet. "You shouldn't avoid exercise," he said, "and then try to compensate by drinking."

According to the authors, there are several plausible explanations for the effect. Alcohol helps raise the levels of high density lipoprotein or H.D.L. cholesterol and lowers plasma fibrinogen levels, which contribute to blood clotting.