Alcohol Use - Risk Factors: Breast Cancer

Content provided by the Faculty of the Harvard Medical School

Alcohol use

Alcohol use

A moderate link exists between alcohol use and breast cancer risk. Studies show that women who have one or more alcoholic drinks a day are 40% more likely to develop breast cancer than women who don't drink at all. The Nurses' Health Study found that drinking as little as half a drink a day increased a woman's breast cancer risk by 30%.

Alcohol and breast cancer risk The risk of breast cancer begins to increase with as little as half a drink per day. Source: Nurses' Health Study

Scientists still don't know how alcohol increases breast cancer risk, but they think there are three possible mechanisms. One is that alcohol can raise the amount of estrogen in the blood, and anything that increases long-term exposure to estrogen can increase breast cancer risk. Another is that alcohol somehow makes breast cells more vulnerable to carcinogens, or cancer-causing agents. Still another theory is that alcohol interferes with the body's ability to use folate, a vitamin that has been linked to cancer prevention. The Nurses' Health Study and others have found that women who drink and also take extra folate have a lower risk for breast cancer than other women who drink.Reducing alcohol intake is one of the few steps you can take to lower your breast cancer risk.

Weight gain

Avoiding weight gain during your adult years can help reduce breast cancer risk. In the Nurses' Health Study, weight gain was linked to an increase in breast cancer risk for postmenopausal women. Those women who had gained more than 45 pounds since age 18 had a small increase in risk of developing breast cancer. The more weight gained, the higher the risk. For women who had gained more than 45 pounds and had never used postmenopausal hormones, the risk was double that of women who done neither.

Researchers think that extra weight increases levels of estrogen. Although a woman's ovaries stop producing estrogen after menopause, fat tissue continues to produce hormones that are converted to estrogen. The more weight a woman puts on after menopause, the more estrogen her body produces.

Sedentary lifestyle

Research suggests that sedentary women are at higher risk for breast cancer than women who are physically active. Most studies have shown that higher exercise levels lower the risk of breast cancer by an average of 30%-40%. But other factors, such as genetics and diet, may be influencing these results. The strong­est evidence for exercise lowering risk is in younger, premenopausal women. A routine of regular, very strenuous exercise during the reproductive years may lessen a woman's risk of breast cancer. This is largely because heavy exercise can delay the onset of menstruation, lengthen the time between periods, or decrease the number of menstrual cycles. All these things reduce estrogen exposure. Physical activity might also protect against breast cancer by bolstering the immune system.

Toxic exposures

Links between breast cancer and environmental toxic exposures have not been firmly established. Studies have been inconclusive. In fact, the Nurses' Health Study found no link between breast cancer and either DDT or PCB.

But, smoking for many years may increase the risk of breast cancer. One study published in 2002 found that the risk of breast cancer was 60% higher among women who had smoked for 40 years than among women who had never smoked. The findings were not conclusive, but because smoking raises the risk of lung cancer and heart disease, it makes sense to avoid tobacco.

Scientists have looked at a variety of other exposures (including electromagnetic fields, and silicone breast implants) but have reported no conclusive results linking any of these exposures to breast cancer.

Last updated:	April 23, 2007