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Moderate alcohol use is associated with a modest rise in breast cancer risk, study finds

A new report suggests that drinking small amounts of alcohol is associated with an increased risk of developing breast cancer.
CC/Flickr/Camp Darby
A new report suggests that drinking small amounts of alcohol is associated with an increased risk of developing breast cancer.

Talk about driving a woman to drink.

For many years, we women have been advised that a one-a-day serving of alcohol (preferably a glass of red wine) would help lower our risk of heart disease. But we’ve also been warned not to drink more than that, because doing so would raise our risk of other illnesses, particularly breast cancer.

Now, along comes a new study, published today in the Journal of the American Medical Association (JAMA), that reports that drinking even small amounts of alcohol — as little as three drinks a week — is associated with an increased risk of developing breast cancer.

The study’s authors, led by Dr. Wendy Chen, an assistant professor of medicine at Harvard Medical School, suggest that alcohol may raise the risk of breast cancer through its effects on circulating estrogen levels in the body.

Interesting, yes. But a reason to give up recreational drinking altogether? No. For although this study’s findings are worth our attention, the increased breast-cancer risk that it found for moderate alcohol use was small. Furthermore, this was an observational study, which means it can’t definitely prove one thing causes another. Other, as-yet unidentified, factors may explain the increased risk.

The numbers
To examine the association of breast cancer with alcohol consumption, Chen and her colleagues used 28 years’ of data from more than 100,000 women enrolled in the long-running Nurses’ Health Study. After crunching the numbers, they found that the women in the study who consumed the equivalent of three to six glasses of wine a week had a 15 percent increased risk of breast cancer compared to those who drank no alcohol. The women who downed at least two drinks a day had a 51 percent increased risk compared to the abstainers.

The risk was strongest for women who consistently drank throughout the period of the study.

Those may sound like big jumps in risk, but they’re not. For example, the chance of a woman being diagnosed with cancer during her 50s is 2.38 percent, according to the National Cancer Institute. A 15 percent increase, therefore, would raise that risk to 2.74 percent, and a 51 percent increase would bring it up to 3.59 percent.

That last jump in risk — from 2.38 percent to 3.59 percent — means, however, that a woman in her 50s would now have the breast-cancer risk of a woman in her 60s (that is, a “1 in 29” 10-year chance of developing breast cancer rather than a “1 in 42” risk).

The caveats
But, as already noted, this is an observational study, and such studies have several important limitations. The alcohol was not randomly assigned to the women, so it could be that women who drink, even moderately, have other risk factors for breast cancer that abstainers do not. Maybe moderate drinkers are less physically active than nondrinkers, for example. (As the authors of this study point out, however, it’s highly unlikely that a long-term randomized trial investigating alcohol use and women’s health will ever be done.)

The study also relied on the women to self-report their alcohol use, and such reports can be unreliable. In addition, most of the women in the study were white, so the findings may not pertain to other populations of women.

No clear answers
As Dr. Steven Narod, a breast-cancer researcher at the Women’s College Research Institute in Toronto, writes in a JAMA commentary, this study doesn’t answer the question of whether stopping alcohol use later in life — say, when a woman is in her 50s — would alter breast-cancer risk.

Nor does it give women any clear risk-benefit answers about what to do regarding alcohol.

“For some women the increase in risk of breast cancer may be considered substantial enough that cessation would seem prudent,” he writes. “However, there are no data to provide assurance that giving up alcohol will reduce breast-cancer risk. Moreover, it would likely be easier for a woman who consumes 1 drink a week to stop drinking than for a woman who consumes 2 drinks a day. Furthermore, women who abstain from all alcohol may find that a potential benefit of lower breast-cancer risk is more than offset by the relinquished benefit of reduced cardiovascular mortality associated with an occasional glass of red wine.”

He then calls for more research. 

As always, stay tuned.

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