Last week's report that drinking red wine could reduce the risk for breast cancer was just the latest in a long string of studies on the issue.
This week many middle-aged women experienced joy, and maybe even raised a glass, upon reading that red wine might stave off breast cancer. The study, published in the Journal of Women's Health, turns out to be quite small. It's a limited analysis of hormone levels in the blood of 36 premenopausal women who drank red and white wine for one month. Still, the story garnered headlines and enthusiastic posts, as if women wanted this news to be true.
For years now, we -- women who've had breast cancer and fear its recurrence, or who are simply at risk, or who are in the throes of it, still -- have been pummeled by reports about what we should and shouldn't eat or drink or do. A friend who's had breast cancer complains she can't have a glass of wine without her husband glancing over her shoulder. At family gatherings her father looks her way, sternly, if she sips from a tall stemmed glass. One woman I know attends fewer parties lately, tired of saying "no, thanks" to cocktails or champagne that otherwise flows freely.
You can't ethically test the premise that a carcinogen is harmful by giving it to some women and not others.
Some find it easier to stay home, avoiding temptation entirely. This pattern of behavior can compound a breast cancer patient's sense of social isolation, depression, and feelings of inadequacy. The question at hand is whether alcohol really does cause breast cancer in some cases and, for women who've had the disease, if partaking promotes its recurrence.
The issue's been out there -- on our minds, and, for some, tempering behavior -- for some time. In 1998, the French-based, WHO-affiliated IARC reviewed four prospective clinical trials, along with other data, and confirmed a link between alcohol consumption and breast cancer in women. Still, those authors cautioned: "a firm conclusion about a causal relationship cannot be made at present." The evidence supported a correlation, but nothing more definitive.
In November 2011, the Journal of the American Medical Association published findings from the Nurses' Health Study. This large analysis involved over 105,000 women monitored from 1980 until 2008. The investigators found that even moderate alcohol consumption -- as few as three drinks per week -- was associated with a statistically significant, slight increase in breast cancer rates. What's more, the study revealed an apparent dose-response, adding credibility to the carcinogen hypothesis. The more a woman drank over the course of 20 years, the more likely she was to develop breast cancer.
The author of an accompanying editorial, Dr. Steven Narod, referred to alcohol as a "third breast carcinogen." Alcohol followed on his short list only after ionizing radiation and hormone therapy. Still, he avoided absolutisms, advising: "For some women the increase in risk of breast cancer may be considered substantial enough that cessation would seem prudent. However, there are no data to provide assurance that giving up alcohol will reduce breast cancer risk."
In December 2011, an expert panel convened by the Institute of Medicine issued a detailed report on non-inherited, i.e. environmental, causes of breast cancer. There too, alcohol is presented as a clear culprit. A table of opportunities for women to reduce their breast cancer risk includes that women "limit or eliminate alcohol consumption." This comes amidst other ideas for healthy behavior, like avoiding unnecessary radiation, not smoking, exercising more, and not being too heavy, as I have considered elsewhere.
Most recently, the American Cancer Society listed alcohol consumption as a "potentially modifiable" breast cancer risk factor in its 2012 Cancer Facts and Figures; the consensus seems near-universal. So when the report "Red Versus White Wine as a Nutritional Aromatase Inhibitor in Premenopausal Women" appeared last week, some headlines reflected understandable good cheer.
The stated goal of the study was to see if red wine might have hormone-modulating effects similar to those of a class of drugs called aromatase inhibitors (AIs). The researchers postulate that since naturally-occurring AIs occur in grape products including red wine, but not white wine, it would be worth measuring levels of estrogen-modulating chemicals in the blood in women who ingested one or the other.
The clinical trial, carefully completed by the investigators and 36 pre-menopausal, eligible research participants at UCLA, scores high on the "fun" scale, for sure. From the "Methods" section:
In a randomized cross-over design, participants were assigned to either red wine (Cabernet Sauvignon, BV Coastal 2003) or white wine (Chardonnay BV Coastal 2003) in the first cycle, and the other wine for the second cycle.... The wine was obtained in a single batch and stored at room temperature prior to use. Participants were provided with the wine in bottles and asked to consume eight ounces (237 mL) of the assigned wine in the evening with food from day one to 21....
The researchers checked levels of testosterone and various forms of estrogen, including estrodiol and estrone, besides luteinizing hormone and sex hormone binding globulin (SHBG) in the women at distinct points in their menstrual cycles. They observed that red wine was associated with higher testosterone and lower SHBG levels, as compared to white wine. They found no significant difference in estrogen levels. Referring to some principles of endocrinology having to do with feedback at the hypothalamus, they conclude: "These data suggest that red wine is a nutritional AI." Their inference is that red wine might work like some of the commonly used hormone treatments for breast cancer.
More than a bit of a stretch, if you ask an oncologist and breast cancer patient like me. The new data is hypothesis-generating but not definitive, said a breast cancer specialist in a tweet. There's no new information in this study on how hormones influence breast cancer growth.
The underlying problem is that it's hard to prove cause and effect in the context of widespread alcohol use to varying degrees among women in North America today. You can't ethically test the premise that a likely carcinogen is harmful by giving it prospectively to some women and not to others. The correlation is clear enough, but it's also the case that women who drink alcohol tend to be heavier than those who don't. In some communities women who have access to alcohol may also be more affluent, more educated, or more sedentary; these and other potential co-factors aren't easy to dismiss.