7 things you should know about breast cancer risk

3. Alcohol

Women who consume even a few drinks per week have an increased risk for breast cancer. It’s not known exactly why. Alcohol may raise estrogen levels, an important player in the development of breast cancer. It may interact with carcinogens or inhibit the body’s capacity to detoxify them.

Several studies, including the Nurses’ Health Study, suggest that the increased risk for breast cancer associated with alcohol occurs mostly in women who don’t get adequate amounts of the B vitamin folic acid. The same is true for colon cancer risk, which is more common among people who drink. According to Harvard School of Public Health nutrition expert Dr. Walter Willett, people who drink alcohol and get 600 micrograms (mcg) or more of folic acid every day aren’t at increased risk.

What to do? Women at average risk for breast cancer should limit their intake of alcohol to one drink per day. Women who have had breast cancer or are at increased risk for it for other reasons may want to avoid alcohol altogether. If you drink, make sure you get enough folic acid (at least 400 mcg per day), either in your multivitamin or in the form of folate in foods such as leafy greens, peas, dried beans, or enriched cereals and whole-grain products.

4. Vitamin D

There’s mounting evidence that vitamin D helps protect against several types of cancer, including breast cancer. For example, one study found that women who got plenty of vitamin D in early life — either in their diet or by spending time outdoors, where sun exposure triggers vitamin D production in the skin — had a lower risk for breast cancer. Another investigation linked high blood levels of vitamin D with a 50% reduction in risk for breast cancer. Reaching those levels requires more than the recommended intake of 400 International Units (IU) of vitamin D per day for women ages 50–70.

What to do? Experts have already begun to recommend 800–1,000 IU of vitamin D per day for adults, partly out of concern that we aren’t getting enough of the vitamin from sunlight to protect our bones and partly because of its association with reduced cancer risk. Natural food sources of vitamin D are limited, and not everyone can get the amount of sunlight needed to trigger adequate vitamin D production in the skin. The best bet is supplemental vitamin D. A standard multivitamin usually supplies 400 IU; you can get an extra 400 IU in a vitamin D supplement or in a calcium supplement containing vitamin D.

5. Medical risks

Lifetime exposure to estrogen is a risk factor for breast cancer, so there is some concern about women’s use of oral contraceptives and postmenopausal hormone therapy.

The Nurses’ Health Study found that women taking birth control pills have a slightly increased risk of breast cancer, but it falls to average within 10 years of stopping. An analysis published in the Mayo Clinic Proceedings found that premenopausal women who use birth control pills have a slightly increased risk of developing breast cancer before age 50, especially if they started taking them before having their first child.

The Women’s Health Initiative trial showed that long-term use of combined hormone therapy (estrogen and progestin, as Prempro) slightly increases breast cancer risk, although the level of risk drops back to normal five years after stopping the hormones. Estrogen therapy alone does not seem to increase the risk.

Studies have shown that women who took the drug diethylstilbestrol (DES) during pregnancy (to reduce the chances of a miscarriage) have a higher risk of developing breast cancer. Research suggests that the daughters of women who took DES are also at increased risk.

What to do? Birth control pills and hormone therapy have risks as well as benefits. Discuss them with your clinician before deciding whether to take them or for how long. If you know your mother took DES when she was pregnant with you, or if you took DES yourself, let your clinician know so you can discuss a screening schedule.

6. Breast density

Breasts are regarded as dense if they have less fat and more connective and glandular tissue. These features are more common in younger women’s breasts, but they are also found in many older women, especially those taking combined hormone therapy (estrogen and progestin). Breast density is also partly a heritable trait.

For reasons that aren’t fully understood, women with dense breasts are at increased risk for breast cancer. In fact, breast density is trumped only by age and the BRCA1 and BRCA2 gene mutations in the hierarchy of risk factors. One possibility is that dense breast tissue contains more cells and is therefore more influenced by growth factors and hormones that make cells divide.