A new study from the Cancer Epidemiology Unit at Oxford University is issuing an ominous warning to middle-aged women, finding that even light to moderate amounts of alcohol can increase the risk of certain cancers, including breast cancer. Wine drinkers, when measured separately from drinkers of beer and spirits, fared little better in the findings, except for colon cancer. Alcohol consumption did appear to decrease the risk of non-Hodgkin lymphoma, thyroid cancer and the leading form of kidney cancer. After reading the findings, other scientists argued that further research is needed.
Previous studies have shown conflicting evidence on links between wine and cancer. While some research has shown wine can decrease the risk of some cancers and even slow tumor growth in lab tests, others have shown alcohol can elevate the risk of breast cancer.
The new study, published in advance of the March 4 issue of the Journal of the National Cancer Institute, examined the rates of cancer among more than 1.28 million women, ages 50 to 64, in the United Kingdom and compared the rates of cancer across weekly drinking habits. They found that any level of alcohol consumption is linked to a higher risk of cancer of the pharynx, esophagus, larynx, rectum, liver and breast. The risk increased for each drink per day. The study was funded by Cancer Research U.K., the U.K. Medical Research Council and the U.K. National Health Service (NHS) Breast Screening Program.
Lead researcher Naomi Allen cautioned that the study did not examine whether the women who did not develop cancer had other health problems, and she suggests that women should weigh the risks of cancer against possible benefits of alcohol consumption in preventing heart disease. Wine, especially red wine, has been consistently linked with lower rates of cardiovascular ailments. However, "given that in middle-aged women, that is women in their 50s to 60s, the risk of developing cancer, particularly breast cancer, is much higher than the risk of developing heart disease, the risks seem to far outweigh the benefits, at least for this age group," Allen said. That presents women with a difficult balancing act—heart disease is the leading killer of post-menopausal women and studies have found evidence wine may reduce the risk of dementia, another concern for older women.
While past studies have shown a possible connection between breast cancer and alcohol, little is known about the effect of alcohol on risks of other cancers in women. Allen and her team analyzed data from the Million Women Study, which has been gathering detailed information from 1.28 million women ages 50 to 64 who attended breast cancer screenings across the U.K. from 1996 to 2001. After agreeing to participate, the women filled out questionnaires on weekly drinking habits, smoking habits and socio-demographic information.
For the purposes of the study, a single drink was defined as containing an average of 10 grams of alcohol per 100 milliliters. That translates to roughly a 5-ounce glass of wine, half a pint of beer or a 1-ounce shot of spirits. Beverage preference was recorded—30 percent of the women reported drinking only wine and 47 percent drinking a mixture of all three types of alcoholic beverage. The women were asked how many servings they consumed in an average week. A followup survey was completed three years later. Over the next seven years, 68,775 of the women were diagnosed with cancer.
The researchers found that the rate of cancer increased the more the women drank each week and concluded that alcohol is a factor in about 11 percent of breast cancer cases, 22 percent of liver cancer cases, 9 percent of rectal cancer cases and 25 percent of mouth and throat cancers. The results equate to alcohol factoring in at least 15 extra cancers per 1,000 women up to the age of 75, the study finds, which may have been prevented through abstaining.
However, the risk for cancers of the mouth and throat only increased for women who also smoked. Researchers think that alcohol may dissolve some of the toxins in cigarette smoke, making drinking and smoking together more risky than doing either alone.
Alcohol appeared to decrease the risks of non-Hodgkin's lymphoma, thyroid cancer and renal cell carcinoma, the study found. Wine drinkers also had a significantly lower risk of liver cancer than mixed-beverage drinkers, 1 percent compared to 31 percent, the study found. Colon cancer was the one form of the disease where wine appeared protective, with a 7 percent lower risk compared to mixed beverage drinkers, who have a 3 percent added risk.
Drinkers were not compared to nondrinkers, as is typical in this type of study. Instead their risk was evaluated in relation to those who consumed less than two drinks per week. For any level of consumption greater than that, the cancer rates gradually increased as the amount of alcohol consumed increased.
However, the researchers still tracked the rate of cancer among nondrinkers, who were classified with former drinkers, though they did not model it in relation to regular drinkers. "It is well-known that many former drinkers may have given up drinking because they are already ill and therefore constitute a biased group," said Allen. "Indeed, the risks for many cancers, for example esophagus, liver, were higher in nondrinkers than drinkers, presumably because some of these women stopped drinking because they had preclinical cancer. As a result, all analyses were done in drinkers and the risk estimates refer to an additional drink consumed per day among drinkers." While some researchers say that this is an improvement over past studies, others argue that the traditional comparison between drinkers and nondrinkers is more valid.
The overall reaction by doctors, medical institutions and government-linked medical bodies to the study is mixed, with many praising the size and scope of it but cautioning that it has limitations and further research is needed. In an editorial accompanying the study, researchers Michael Lauer and Paul Sorlie from the division of prevention and population sciences at the National Heart, Lung, and Blood Institute in Bethesda, Md., wrote, "From the standpoint of cancer risk, the message of this report could not be clearer. There is no level of alcohol consumption that can be considered safe."
Britain's NHS, which sets recommendations of daily alcohol intake, issued a statement affirming its current guidelines for women who drink: Avoid binge drinking and consume no more than two to three units per day. The NHS also questioned whether the study followed the women long enough.
"The study has only assessed average alcohol intake at two times, three years apart," read the statement. "It is not possible to tell from this whether this is a long-term established drinking pattern, or whether alcohol drinking levels varied over the women's lives."
The Institute of Lifestyle & Health at Boston University School of Medicine also released an opinion on the study, authored by three prominent alcohol and health researchers: doctors Luc Djoussé, Curtis Ellison and Yuqing Zhang. The authors call the study an "important paper" but lament the lack of diversity in the method used for gathering data. For instance, the study only tracked the women's cancer status from point A to point B, without a view to the future. The Boston University team suggests further followup to help determine the "threshold of alcohol intake that may increase the risk of cancers."
Several scientists also noted that the study did not ask women about daily drinking habits. It noted weekly drinking habits and divided the number of drinks by seven. Some researchers have argued that there is a big difference between consuming one drink daily versus seven drinks on Saturday night.
For her part, Allen stresses that her motivation was not to provide advice for women, as her research is localized to only one type of ailment. "My job is to provide the scientific evidence," she said. "We really need to examine alcohol drinking on the risk of heart disease and cancer within the same population before commenting on the overall risk/benefit ratio for women."