Women who raise a glass just a few times a week appear to have a higher risk of getting breast cancer than those who are teetotalers.
A study that looked at the drinking habits and development of breast cancer in more than 100,000 nurses found those who drank more had a small but detectable increase in breast cancer compared with those who drank less.
For women who had a drink a day, the risk was about 1.2 times greater than would have been expected. Over a decade, the change meant the cancer risk increased 0.7 percentage points — to 3.5 percent from 2.8 percent. Not huge, but not nothing. The researchers note the risk is associated with longstanding habits, not drinking a lot over a few weeks or months.
The findings were just published in JAMA, the Journal of the American Medical Association. And they're consistent with some previous research that has suggested a cancer hazard. The latest study checked on a lot of women for many years, which is a strength. But it didn't randomize them to drinking and nondrinking groups, which limits the ability of the researchers to assess cause and effect.
What might be going on? One possibility is that alcohol may boost the level of hormones such as estrogen in the blood, which could raise cancer risks. It may be that exposure to alcohol starting in early in life is a cumulative risk that contributes to cancer that becomes evident after menopause.
An accompanying JAMA editorial asks: Should "postmenopausal women stop drinking to reduce their risk of breast cancer?" There's no clear evidence that would help. And there is evidence of health benefits from moderate drinking, such as protection against heart disease.
Harvard's Dr. Wendy Chen, lead author of the study, offered one bit of advice for those concerned about the cancer hazard. "We didn't see any increased risk of breast cancer at alcohol consumption less than three drinks per week, so that would be a safe amount to tell someone in terms of the breast cancer risk," she said in the video you can watch below.