A research paper presented last month at the American Association for Cancer Research attracted significant media attention because it linked alcohol use to breast cancer risk.

Previous studies have also provided some evidence that alcohol may increase breast cancer risk, and laboratory studies have shown us the mechanism by which alcohol could promote breast cell growth, so this is not really “new news.” However, the new finding does come from the NIH-AARP Diet and Health Study, which is one of the largest studies to ever look at the relationship between diet and health.

The Diet and Health study, which began in 1995, includes 184,418 postmenopausal women. The women answered questions about their daily alcohol use. About 70 percent of the women in the study said they drank alcohol, on average less than a drink a day. About 5400 women in the study have developed invasive breast cancer and the researchers had information about the type of tumor 2391 of these women developed. (Specifically, there were 1,641 who developed ER+/PR+ tumors; 366 women with ER-/PR- tumors; 336 women with ER+/PR- tumors; and 48 women with ER-/PR+ tumors.

The researchers reported that moderate alcohol consumption, which they defined as one or two drinks per day, increased a woman’s risk of developing a breast cancer tumor that is hormone-sensitive (ER+/PR+). (Overall, about 70% of all women who are diagnosed with breast cancer have this type of tumor.)

Compared to non-drinkers, women who consumed less than one drink daily had a 7% higher risk of developing breast cancer. Those who had one to two drinks a day had a 32% increased risk, while those who had three or more daily drinks had a 51% increased risk. The increased risk was found no matter what type of alcohol (wine, beer, etc.) a woman drank.

To put this into some perspective: A woman between the ages of 60 and 69 has a 3.65% percent chance—1 in 27 —of developing breast cancer. If she had less than one drink a day, and her risk increased by 7%, she would now have a 3.9% chance—still 1 in 27—of developing breast cancer. If she had one to two drinks a day and risk increased by 32%, she would now have a 4.8% chance—1 in 20—of developing breast cancer. And if she had three or more drinks a day, she would not have a 5.5% chance—1 in 18— of developing the disease. But that’s just what this study found. And although a number of other studies have found a link between alcohol and breast cancer risk, and there are scientific explanations for why this might be true, correlation does not equal causation. There might still be something else going on.

We also don’t yet know whether alcohol increases risk if you are already at risk or of having a recurrence. This study couldn’t tease out what a woman’s actual risk was. It just compared drinkers to non-drinkers. This means we don’t really know enough other than to say that if you drink more than one glass of wine a day and are worried about your breast cancer risk, this study might prompt you to cut down or quit.

The National Cancer Institute bulletin recently published a good piece in its newsletter about the research on alcohol and breast cancer. You can read it here.

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