05/13/2009 05:12 am ET | Updated Nov 17, 2011

Dueling Docs: Is Drinking Linked to Breast Cancer?

The Issue
Alcohol and the Risk of Breast Cancer

The Facts
Is drinking good for you - or not? Seems that nothing short of Prohibition can put an end to the debate. For years, kicking back some booze seemed positively virtuous: a host of studies show that moderate drinking may ward off heart attack and stroke, and possibly dementia and diabetes.

But before you drink to that, consider whether alcohol may also harm the breast. A report in last month's Journal of the National Cancer Institute suggests that as little as one extra glass of wine, beer or hard liquor a day can increase a woman's odds of developing of breast cancer, a finding that pins alcohol on as many as 11% of all breast cancer cases. The study, which followed more than 1 million British women age 50 to 64 for an average of seven years, is one of the largest and longest on the subject. It is also one of the only to show a breast cancer link with just a small amount of imbibing.

What to do?

Two doctors debate the issue: Naomi Allen, the study's lead researcher and cancer epidemiologist at the University of Oxford and Lisa Schwartz, MD, associate professor of medicine at the Dartmouth Institute for Health Policy and Clinical Practice and author of Know your Chances: Understanding Health Statistics (University of California Press; 2008).

The Debate

Dr. Allen:

"Most of the work on the link between cancer and alcohol has been on men who are heavy drinkers. What hasn't been known are the chances of developing cancer for the woman on the street who is only drinking a moderate amount.

"That's what we looked at and we found that for every extra drink a day, a woman's risk of breast cancer goes up by 1.1%. We already knew that by the time a woman is age 75, her risk of breast cancer is 9.5%. Add one glass more of alcohol and that risk increases to 10.6%; two glasses, 11.7%. For every drink you consume, your risk of breast cancer continues to go up."

These are tricky statistics. Allen is talking about the extra drink a day, beyond the amount consumed by the average woman in the first place -- that one who has a 9.5% chance of developing breast cancer by age 75. Still, says Allen "A 1.1% increase above the average risk may sound small, but it translates to 20,000 extra cases of breast cancer a year."

What about all those women in France where breast cancer doesn't appear to be epidemic and who seem to drink wine like it's Coke by the caseload from Costco? "Fact is," says Allen, "there's no real evidence that French women are drinking more than women in the US or UK. In my study, women were drinking an average of one drink a day. Are French women really drinking more? We don't know."

One of the reasons Allen is so convinced of her findings is that there's a plausible explanation. "There is emerging evidence that alcohol increases a woman's blood level of estrogen. High levels of estrogen in the blood are a known risk factor for breast cancer."

Should women stop drinking altogether then? Drinking may still ward off heart disease, but for middle aged women, the odds of developing breast cancer is higher than the odds of suffering a heart attack. Says Allen, "You may be better off not drinking at all, but it's too early to give a precise answer." Then too, Allen's study found a decreased risk of thyroid, kidney and non-Hodgkin's lymphoma among women who drank moderate amounts. "Those cancers are rarer than breast cancer to begin with, but alcohol seemed to lower their incidence."

Dr. Schwartz:

"I think these researchers are making the link between drinking and cancer look scarier than it really is."

Schwartz notes that the researchers compared women in the study to the average woman, whose risk of cancer is 9.5% by the time she is 75.

"We don't even know how much the average woman is drinking in the first place. What's important is to look at what really happened to the women in this study. Let's look at how much they drank in absolute terms and then look at their risk of developing breast cancer over the length of the study."

"When you do that," says Schwartz says

"you find that for an individual woman, the increased chance of breast cancer from modest drinking -if it exists- is actually small. Women who drank 1 or 2 glasses of alcohol a week for an average of 7 years had the same chance of getting breast cancer as women who drank none. Meanwhile, women who drank once a day or every other day--3 to 6 glasses a week--had a 97.9% chance of avoiding breast cancer compared to women who drank one or two glasses a week. They had a 98% chance of avoiding breast cancer. This is really a tiny difference."

She continues: "I think we can be suspicious about whether this study is really true. Meantime, all the other studies show a much smaller risk of breast cancer from alcohol than this one does,"

Another red flag for Schwartz is what she described as "some level of inconsistency. The researchers found that non-drinkers are at a greater risk of all cancers combined. I see this as a potential problem with the results."

"I also worry that what the researchers are observing is not really the effect of alcohol on breast cancer but something about the women in the study. The women were recruited from mammogram screening centers, but we don't know how often these women were screened. Was it every three years, or did some women wait longer? As socio-economic status goes up, screening does, too. As does drinking. And the more screening mammograms you have, the more likely a cancer will be found. So, we don't know if the finding of more breast cancer among the drinkers is because of their drinking or because they are screened more often. That could be an explanation for this phenomenon."

The bottom line, says Schwartz is that "as an individual you want to know what your cancer risk is if you drink alcohol. The researchers in this study made a statistical model that spit something out, but when I look at the numbers, I don't agree with their results."