Moderate alcohol consumption--perhaps as few as three drinks a week--can significantly increase a woman's chances of developing breast cancer, according to two major new studies being published today by researchers at Harvard University and the National Institutes of Health.
The studies in this week's New England Journal of Medicine also found that women who have not yet reached the age of menopause appear to have a higher risk of breast cancer as a result of drinking alcohol than post-menopausal women, and the risk increases in proportion to the amount of alcohol consumed.
While the reports present the strongest evidence yet of a link between alcohol and breast cancer, the authors said the data are not sufficiently conclusive to be used as the basis of specific recommendations on drinking.
Nevertheless, the prestigious weekly medical publication urged in an accompanying editorial that women with known risk factors of developing breast cancer to "curtail their alcohol ingestion." Such factors include a family history of breast cancer, childlessness, a late pregnancy, early menopause or obesity.
Two Los Angeles cancer experts noted that such epidemiological studies can have large margins of error, and one of them, Dr. John A. Glaspy of UCLA, said the latest results do not represent "a risk to panic about." Breast cancer is the second leading cause of cancer deaths among females, striking one in 10. According to the American Cancer Society, about 41,000 American women will die of the disease this year.
The government study involved 7,188 women--a sampling considered to be an accurate cross-section of the country's female population in terms of age, race, educational, economic levels and other important demographic features. Between 1971 and 1984, the study period, 131 of the women got breast cancer.
The study found that the consumption of any amount of alcohol raised a woman's chances of breast cancer by 50% to 100%, compared to a nondrinker.
The investigators, led by Dr. Arthur Schatzkin of the National Cancer Institute, concluded that even women who consume fewer than three drinks a week face a 40% to 50% higher risk of breast cancer. The highest risk group was women who had three or more drinks per day.
One Drink Defined
By one drink, the researchers meant one ounce of hard liquor, 12 ounces of beer or five ounces of wine.
The Harvard study was based on the dietary and drinking habits of 89,538 women nurses in 1980. During the next four years, 601 of them got breast cancer, and their habits were compared with those of women who remained healthy.
This study found that women who had one or more drinks a day had a 60% higher risks of developing breast cancer than nondrinkers.
"Sixty percent is a big-sounding effect, but a small number in epidemiological terms" because most epidemiologists generally do not consider a risk to be significant until that increased risk reaches several hundred percentage points, according to Dr. Brian Henderson, an epidemiologist who is director of the USC Comprehensive Cancer Center.
"We are reluctant to feel confident about any number of that magnitude," he said, referring to the 60% figure.
However, Walter C. Willett, the Harvard researcher, argued: "But I also think it's a rational decision to say, 'Yes, there is some uncertainty, but I'm going to play it safe and reduce my drinking.' "
Effect on Heart Attacks
Paradoxically, other public health studies involving alcohol have shown that modest consumption seems beneficial in preventing heart attacks, and this was noted in the New England Journal editorial written by Saxon Graham, a public health expert at the State University of New York at Buffalo.
Although more than a dozen previous studies have shown an association between drinking and breast cancer, the latest are especially noteworthy, he said, because they help to resolve some of the weaknesses of the earlier ones. For example, some of the earlier studies did not account for other risk factors in calculating results, and none was conducted with a representative sample of the U.S. female population.
In the new studies, the effect of alcohol was seen after other risk factors for breast cancer had been ruled out.