Researchers from Kaiser Permamente in Oakland, California presented evidence at the European Cancer Organization meeting in Barcelona suggesting that 1 or 2 drinks a day (wine, beer, or hard liquor) increase a woman’s risk of breast cancer by 10 percent, and 3 or more drinks a day increase it by 30 percent.

The data has yet to be published, but the results were reported widely by the mainstream media. How alcohol might contribute to breast cancer is unknown, but drinking alcohol does raise blood estrogen levels, which theoretically might promote breast cancer.

Unfortunately, all studies of alcohol and breast cancer, even those published in prestigious journals, are observational. In other words, researchers count breast cancer cases among women who do and do not drink, and track how much the drinkers consume (usually based on self-reporting, which is known to be unreliable). The studies take into account factors such as age, weight, smoking status, and hormone use. This type of research cannot determine cause and effect. It can only conclude that women who drink certain amounts of alcohol have a higher risk of breast cancer but it does not mean alcohol causes breast cancer.

According to study author, Arthur Klatsky, MD, “studies have been all over the place with regard to breast cancer and risk. Where the threshold lies, I don’t know.”

The American Cancer Society lists alcohol as a risk for breast cancer, but most of the evidence applies to heavy drinkers. Should you forget about breast cancer and have a drink each day to protect your heart? If you are a light or moderate drinker, should you quit in order to reduce your risk for breast cancer?

No one knows the answers. But to be on the safe side, consider the following:

• If you choose to drink, limit the amount to no more than one drink a day.
• If your breast cancer risk is high, you might want to quit drinking altogether or have only an occasional drink.
• Any increase in risk is concerning, but should be kept in perspective. The average woman has a 2.7 percent (1 in 37) chance of developing breast cancer during the next ten years. If she has 1 or 2 drinks a day her risk would increase to 3 percent (1 in 33). In other words, among 1,000 women age 50 who drink 1 or 2 drinks a day for 10 years, an extra 3 cases of breast cancer may occur.