Alcohol is classified as carcinogenic to humans by the International Agency for Research on Cancer. Several large epidemiologic studies have indicated that consumption of each additional 10 g of alcohol per day – just less than the standard US drink of 14 g of alcohol – increases a womans risk of breast cancer. A review of epidemiologic research on human carcinogenesis supports two different mechanistic interpretations that have fundamentally different implications for the development of breast cancer.
Results will be published in the January 2013 issue of Alcoholism: Clinical & Experimental Research and are currently available at Early View.
"The idea that consuming less than one drink per day significantly increases breast cancer risk is based on epidemiologic studies relating self-reported alcohol consumption and breast cancer in women," explained Philip J. Brooks, program director in the Division of Metabolism and Health Effects at the National Institute on Alcohol Abuse and Alcoholism (NIAAA), as well as corresponding author for the study.
There are, however, problems with self-reporting. "Self–reported consumption is known to underestimate actual consumption," he said. "In other words, we dont really know how much the women in these studies were actually drinking. For example, there is a major difference between drinking several drinks on a single day and nothing on others versus literally drinking one drink per day. Binge-type drinking on some days and not drinking on others does not average out to moderate drinking. Notably, a recent epidemiologic study from Harvard found that women who reported binge-type drinking had slightly elevated breast cancer risk than those who did not."
- Alcohol can have both damaging and beneficial effects on the body.
"When wine, beer, or distilled spirits are ingested, alcohol goes to virtually every cell in the body," explained Brooks. "Since different cells in the body have significantly different functions, it is not surprising that alcohol can have multiple different effects, both toxic and beneficial, depending on the dose. The nature of these effects depends upon many factors, including the amount of alcohol consumed and the drinking pattern, whether it is taken with food or on an empty stomach, as well as the persons age, gender, and developmental state. For example, heavy binge drinking for a few hours can cause brain damage and even death, while moderate drinking can beneficially change HDL cholesterol and impact bone healing within a few weeks."
Susan M. Gapstur, vice president of the epidemiology research program at the American Cancer Society, agreed that alcohols effects may seem confusing. "As mentioned by the authors, there is considerable evidence linking alcohol intake, even at moderate amounts, to an increased risk of breast cancer," she said. "However, complicating any recommendations for alcohol and cancer-risk reduction is the decreased risk of coronary heart disease associated with low to moderate intake of alcoholic beverages. Certainly we need this kind of research to clarify these issues."
- Human carcinogenesis typically develops over decades.
"Some of the largest epidemiologic studies involved asking middle-age postmenopausal women about their current alcohol consumption, then assessing breast cancer diagnoses over the next five to 10 years," said Brooks. "However, it takes roughly 20 years or more to go from a normal cell to a clinical diagnosis of cancer. Therefore, the breast cancers that these women were diagnosed with in these studies could not have been caused by the alcohol they reported drinking at the beginning of the study, that is, causing a normal cell to become a cancer cell."
- There are at least two possible explanations for epidemiologic findings.
"One explanation is that some of the women had undiagnosed breast cancers at the time that the study began, and that alcohol drinking increased the probability of breast cancer diagnosis, perhaps by making the tumors grow faster," said Brooks. "The other explanation is that lifetime drinking, including drinking earlier in life, increases breast cancer risk, consistent with several earlier epidemiologic studies. Since alcohol drinking is typically a lifelong habit, asking postmenopausal women about current drinking is essentially asking about lifetime drinking."
These two possibilities have very different implications for womens health, Brooks said. "If the first possibility is correct, understanding how alcohol drinking increases the growth rate or invasiveness of a latent tumor – which could be initiated by numerous different factors – is important, because it is possible that drugs could be developed that would interfere with these effects," he said. "However, if breast-cancer risk in postmenopausal women is the result of drinking earlier in life, then stopping drinking will not impact their breast-cancer risk."
Furthermore, Brooks added, drinking is a lifetime habit, and drinking patterns can change over time. "Binge type drinking typically occurs in younger people, and becomes less common as people age," he said. "To be blunt, binge drinking by younger women could increase the risk of breast cancer later in life. It is important to stress this point now, because unfortunately binge drinking by young women is on the rise."
That said, both Books and Gapstur noted that even if moderate drinking can have health benefits, this would not justify beginning to drink for alcohols health benefits.
"There are other ways to improve cardiovascular health without drinking alcohol, such as diet and exercise, and these should be discussed with a personal physician," said Brooks.
"Also consider avoiding smoking, consuming a low saturated- and trans-fat diet, maintaining a healthy weight, staying physically active, and controlling blood pressure and lipids," added Gapstur. "Therefore, the American Cancer Societys recommendation for women to limit intake to no more than one drink per day remains warranted."
"In summary," added Brooks, "since other research has shown that moderate drinking can have cardiovascular health benefits, and may also be associated with healthy aging, it is not clear that abstaining from alcohol would have an overall positive impact on the health of postmenopausal women who are moderate drinkers. Women and their health care providers need to consider the risks and benefits of moderate alcohol drinking in the context of overall health impact at different stages of their lives."