Understanding your chances of developing breast cancer—and what you can do to prevent it—can help you take action, and maybe also give you peace of mind.

pink ribbon shape with girl paper doll on pink background for Breast Cancer Awareness
Credit: pinkomelet/Getty Images

Although you probably know those pink ribbons in October are for Breast Cancer Awareness Month, you might not know much about your personal risk of the disease, which affects one in eight women. Breast cancer is more common after menopause, but your risk can by modified by what you do now. Plus, younger women can get breast cancer, too. We asked Graham A. Colditz, DrPH, MD, MPH, Breast Cancer Research Foundation Investigator and associate director of Prevention and Control at the Alvin J. Siteman Cancer Center at Washington University in St. Louis, to uncover the factors you can—and can't—change to reduce your risk now and in the future.

1. Your weight is a major factor

The relationship of weight to breast cancer is complicated. Being overweight actually lowers the risk in premenopausal women, but "the clearest data shows that overweight and adult weight gain increase the risk of breast cancer after menopause," Dr. Colditz says. "And because the majority of breast cancers are diagnosed in postmenopausal women, it's important to work to maintain a healthy weight throughout life." The long-term benefits of keeping your weight in check outweighs anything else, he says.

2. Exercise reduces your risk

One of the best ways to help keep weight healthy is also linked to a reduced risk of breast cancer: vigorous physical activity. "It's not perfectly understood how exercise lowers breast cancer risk, but we have some ideas," Dr. Colditz says. "It can help with weight control, help control blood levels of certain breast cancer-related hormones, and improve immune function, which may help fight off infections linked to cancer."

3. Healthy foods may be preventative

Eating a plant-based diet with less meat could also lower your risk of breast cancer. "Growing evidence supports a role of vegetables and fruits with fiber and carotenoids being protective in quite a few studies," Dr. Colditz says. "Thus, a healthy diet based on grains and lower animal protein will likely reduce the risk for breast cancer."

4. Alcohol increases your risk

Even moderate drinking has been shown in recent studies to increase your risk of breast cancer. "Alcohol is a known carcinogen for breast tissue and other tissues in the body," Dr. Colditz says. Plus, alcohol consumption drives up hormone levels. "Circulating hormone levels are directly related to breast cancer risk as they increase cell proliferation and tumor growth," he says. Needless to say, smoking increases breast cancer risk as well.

5. The pill may increase your risk

While the pill has many benefits, your risk of breast cancer does go up slightly while you are taking it. "This risk goes away, though, not long after stopping, generally within five years," Dr. Colditz says. "The actual pathway for this increase is not known, though use of oral contraceptives modifies circulating hormone levels that in turn can modify breast cancer risk."

6. The risk of fertility treatments is unknown

Many women taking hormones to help them get pregnant are concerned about how the drugs could affect their cancer risk. "It is currently not clear how, or if, fertility treatments that stimulate the ovaries impact the risk of breast cancer," Dr. Colditz says. "It is an active area of research, with some studies showing that fertility treatments increase risk, and other studies showing that they don't."

7. Breastfeeding lowers your risk

If you can breastfeed, it lowers your breast cancer risk. "Women who breastfeed have sustained lower levels of the hormone prolactin, and high prolactin levels are directly related to breast cancer, as they are important in cell division and proliferation of breast tissue," Dr. Colditz says. The greatest benefit comes from breastfeeding for one year or more total across all children.

8. Knowing your family history is important

You may know your chance is greater if your sister or mother had breast cancer, but be sure to look at both sides of your family to assess your true genetic risk. "For some women with a strong family history, cancer risk can be significantly higher," Dr. Colditz says. "Important markers for this type of family history include having multiple family members with cancer, especially at younger ages; a single family member who has had multiple different cancers; and breast cancer in male family members." If that's the case, your doctor may send you for genetic counseling or testing, and you might need to start breast cancer screenings early and more often.

9. Your period is linked to your risk

The age at which you started your period, as well as the age you stop, is linked to your breast cancer risk. "A woman's reproductive history is a marker of her exposure to hormones and the associated monthly cycle of hormones and breast cell divisions," says Dr. Colditz. Basically, the more cycles you have over the course of your life, the greater your risk.

10. Pregnancy alters your risk

Although being pregnant drives up hormone levels temporarily, pregnancy may also be beneficial. "After having a first baby, hormone levels are slightly modified, cells divide more slowly and have more time for repair of DNA damage," Dr. Colditz says. Your age at first pregnancy is also a factor. "The longer the interval from first menstrual period to first baby, the larger the number of menstrual cycles with the maximum rate of cell division and the minimum time for repair, which increases breast cancer risk," he says.

11. Breast density is important

One new factor coming to light is how dense your breasts are—and not just because it makes cancer harder to see on mammograms. "It is a measure of how much breast tissue and connective tissue are in the breast compared to how much fat tissue," Dr. Colditz says. "Women with high breast density have been found to have around three to four times the risk of breast cancer compared to women with low breast density."

If you have any concerns about how these factors influence your individual risk, talk to your doctor.