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Kristin Anderson

University cancer epidemiologist Kristin Anderson says the increased risk of breast cancer among moderate drinkers is real, but not great.

A drink a day may bring the doctor your way

U researchers comment on a recent study linking alcohol to breast cancer

By Deane Morrison

October 1, 2007

The headlines Friday (Sept. 28, 2007) bore bad news for women who drink: A large study by Kaiser Permanente doctors showed that a single daily alcoholic drink of any kind raised the risk of breast cancer by 10 percent, and three or more drinks jacked it up to 30 percent. Yet alcohol, according to other studies, may help lower the risk of heart attack. So what's a woman to do? With this question in mind, we asked University cancer epidemiologist Kristin Anderson and cardiologist Daniel Duprez to sort out the science behind the scoop. A major finding of the study was that whether a woman drinks beer, wine, or spirits, alcohol raises her breast cancer risk the same. This came as no surprise to Anderson, a Distinguished University Teaching Professor in the School of Public Health. "There have been more than 100 studies on alcohol and breast cancer," she says. "This is consistent with past data. I was in a collaborative study by Oxford University that came out in 2002 in the British Journal of Cancer. That was a much larger study, analyzing results from 53 previous studies of 58,515 women with cancer and 95,067 without. We got similar results." The Kaiser Permanente study was based on 70,000 patients.

"About 4 percent of breast cancer in developed countries is attributable to alcohol," Anderson says. "It's important to note that that is a small proportion of the disease."

Stories in the Minneapolis Star Tribune, the St. Paul Pioneer Press, and the New York Times (online) all reported the 10 percent and 30 percent increases in risk, but none reported the baseline risk. According to the American Cancer Society, U.S. women overall run one chance in eight, or 12.5 percent, of developing breast cancer and one in 34, or 2.9 percent, of dying from it. Suppose for simplicity's sake that a nondrinking woman has few risk factors and a 10 percent chance of developing breast cancer. On average, such a woman who began quaffing a drink a day would raise her risk by 10 percent over the baseline, to 11 percent. If she added three drinks a day, her risk would rise from 10 to 13 percent. The Star Tribune article quoted Yan Li, co-author of the Kaiser study, as saying that one possible mechanism by which alcohol could raise the risk of breast cancer is by changing the metabolism of estrogen, which promotes the growth of some breast cancers. Though not disputing that, Anderson says other factors may also play a role. "Alcohol consumption has a negative impact on the absorption, utilization, and excretion of folate, a vitamin necessary for maintaining the integrity of DNA," she states. Also, alcohol may increase the activity of enzymes that activate carcinogens. And, she adds, some breakdown products of alcohol, notably a chemical called acetaldehyde, have been labelled carcinogenic. According to the 2002 study Anderson took part in, "about four percent of breast cancer in developed countries is attributable to alcohol," she says. "It's important to note that that is a small proportion of the disease. If you live in a society that has no drinking, no cases will be attributable to alcohol." The American Cancer Society estimates that in 2007 there will be approximately 178,480 new cases of breast cancer in the United States, she adds. As for alcohol's role in lowering heart disease risk, Duprez says there is evidence to support it, but many questions remain. For instance, he says it is well known that alcohol increases levels of HDL--the "good cholesterol"--but nobody knows whether that is the mechanism behind the correlation between alcohol and lowered risk. Red wine has been seen as especially "protective," but it could be high levels of antioxidants in red wine or some substance in grapes that does the trick. "The key is this: A maximum of one glass of alcoholic beverage a day for women and two for men is associated with cardioprotection, but this has never been shown in a randomized trial," says Duprez, an assistant professor of cardiology. "Alcohol should not be universaly prescribed for health enhancement. There is a complete lack of randomized data" with respect to exactly how it might protect the heart. For Anderson, the Kaiser Permanente story is an opportunity for women to think about how they live their lives. "People should use this data to reflect on their lifestyle and decide if it would be prudent to change their habits," she says. "There are other risks associated with drinking more than three drinks per day. You have to look at the weight of evidence and at other studies, if possible. "Most risk is at higher intakes [of alcohol]. An increase of 10 percent isn't much, but it's a real risk because it's been seen in many other studies."