Women who worry that regular drinking might increase their chance of developing breast cancer can take comfort in the latest research. Scientists in Melbourne, Australia, report that eating high amounts of folic acid--which is found in leafy greens, citrus fruits, beans and peas--may wipe out any risk of breast cancer attributable to moderate alcohol consumption.
"Any adverse effect of alcohol consumption [on breast cancer risk] may be reduced by sufficient dietary intake of folate," wrote the authors, led by Laura Baglietto, senior researcher at the Cancer Council Victoria, a research charity. Folate, or folic acid, is a B vitamin that helps produce red blood cells and create and maintain the DNA of new cells.
In fact, the study, which was published in the Aug. 8 issue of the British Medical Journal, found that the women who averaged two or three drinks a day and who consumed Australia's recommended daily allowance of folic acid even had a somewhat lower risk for breast cancer than the nondrinkers who consumed the same amount of folate.
The researchers wanted to look at whether folic acid, which is believed to reduce the chance of breast cancer, would interact in the body with alcohol, which the authors consider to be "a known risk factor" for breast cancer although ethanol itself is not a carcinogen.
Whether alcohol increases a woman's risk of breast cancer through some complex process has yet to be definitively proven, and researchers' opinions vary. Dr. R. Curtis Ellison of the Boston University School of Medicine, a noted wine-and-health researcher whose work found light drinking doesn't increase breast cancer risk, said there are few human studies on the subject, and those results conflict.
The Australian team examined data on 17,447 women who participated in the larger Melbourne Collaborative Cohort Study, which was started in the 1990s to examine the role of dietary choices on cancer risks. In that study, volunteers were recruited via electoral rolls, as well as through advertisements in the local media. The participants provided detailed information on their food and drink habits over a 10-year period or until their deaths. Other information, such as education, income levels and whether they had children was also recorded.
For the new research, the scientists chose women who at the beginning of the study were ages 40 to 69 and had not been diagnosed with cancer or diabetes; they excluded anyone whose habits had changed greatly over the 10-year period.
The women were categorized according to their average levels of alcohol consumption: abstainers, one to 19 grams of ethanol per day (defined as low by the Australian researchers), 20 to 39 grams of ethanol per day (medium, though this amount is higher than the U.S. government's definition of moderate consumption for women) and more than 40 grams per day (heavy). A standard alcoholic beverage, such as a 4- or 5-ounce glass of wine, contains an average of 10 grams of ethanol.
The women were also grouped by how much folic acid they consumed per day on average: 200 micrograms, 330 micrograms or 400 micrograms, which is Australia's recommended daily allowance for women in that age group. Two-thirds of the participants did not consume the government's suggested daily amount of folates. "Few women in our study used folic acid supplements, and our study was done before folate fortification became common in Australia," Baglietto said.
Over the 10-year period, 537 of the women were diagnosed with breast cancer. By comparing their diets and drinking patterns to those of women without breast cancer--using several different methods, with similar results--the researchers were able to come up with a "hazard ratio" to gauge a woman's risk of breast cancer.
In short, they found that a woman's risk of breast cancer increased slightly, by 3 percent, with each drink they had per day. At lower levels of consumption, less than two glasses per day, they considered this increase "not significant."
The team also found that, for the drinkers in the "medium" category, this increased risk was wiped out if the women consumed 330 micrograms or more of folic acid per day. Compared with nondrinkers who consumed the same amounts of folic acids, women who drank 20 to 39 grams of alcohol per day showed a 15 percent lower chance of breast cancer if they ate an average of 330 micrograms of folates per day and a 19 percent lower risk if they ate 400 micrograms per day.
Even the heavy drinkers saw a reduced cancer risk if they consumed 400 micrograms a day of folic acid, although the number of women in this group was rather small, and their results may not be representative. However, the authors did not observe a significant protective benefit from a high intake of folates for the drinkers in the "low" category.
Among the women who consumed only 200 micrograms per day of folic acid, the nondrinkers and women who drank low-to-medium amounts showed basically the same risk of developing breast cancer. For women who drank more than 40 grams of alcohol per day, the risk doubled.
"Our study suggests that alcohol is only associated with breast cancer risk for women who have low intakes of dietary folate," Baglietto said.
The authors said they aren't sure exactly how ethanol and folic acid interact with or counteract each other inside the body to yield this possible anti-carcinogenic effect, but they suspect several metabolic mechanisms may be involved. For example, Baglietto believes a metabolite of alcohol may destroy folate before it is properly digested; as that can leave the body more vulnerable to disease, she feels regular drinkers need to increase their consumption of folate to compensate.
Ellison, who read Baglietto's research but was not involved with it, said he believes the findings are important because they explore a way in which moderate drinkers may help protect themselves. "This paper supports other studies showing a weak relation between increasing alcohol intake and the risk of breast cancer," he said, "and more importantly, an interaction between alcohol and folate in their relation to the risk of breast cancer."
While Baglietto said her organization encourages women to reduce their breast-cancer risk by reducing alcohol intake, Ellison cautioned most women against that, citing the health benefits of moderate drinking seen in other studies. "If a post-menopausal woman stops drinking to prevent breast cancer, she is likely to die sooner rather than later," he said, "since she is stopping a preventative measure for heart disease and stroke, much more common causes of death than breast cancer."