Pregnancy and Breastfeeding
Pregnancy before age 30 and breastfeeding reduce a woman's total number of lifetime menstrual cycles, which is thought to be the reason they help lower your risk. The hormone estrogen fuels 80% of all breast cancers. Since pregnancy and lactation reduce your estrogen levels, your risk is decreased each time you are pregnant and while you are nursing your baby.
How Long Should I Breastfeed?
While this is a very personal decision, studies show that breastfeeding for one and a half to two years over one's lifetime will reduce your risk of breast cancer slightly.
A study of Chinese women found that their breast cancer incidence dropped by 63% when they breastfed for six years. Though that tends to be longer than most choose to do so, your reduced risk can be determined by the cumulative amount of time you've spent breastfeeding over the course of your life. For example, if you had three babies and nursed each for six months, your cumulative breastfeeding time of one and a half years would serve to reduce your risk of developing breast cancer.
How Does Breastfeeding Help Prevent Breast Cancer?
There are several theories about how breastfeeding protects you from developing breast cancer:
- Your lifetime exposure to estrogen is reduced, which decreases the possibility of developing estrogen-fueled breast cancer.
- Your hormone balances are different during lactation, resulting in fewer menstrual cycles and less estrogen exposure.
- Environmental carcinogens that are stored in fat, which makes up a great part of the breast, cannot be efficiently stored in lactating breasts.
- Breastfeeding may cause changes to breast cells that make them more resistant to cancer-related mutations.
If you are still fertile after treatment for breast cancer, you might worry about becoming pregnant. Studies have shown that hormones produced during pregnancy and breastfeeding do not cause a recurrence of breast cancer. Breast milk will not carry breast cancer cells, so your baby will not be affected by nursing. You should be able to breastfeed with your healthy breast, as well as produce enough milk to feed your baby. Just keep a close eye on baby's health and weight gain, and take any needed supplements.
Not a Gold-Plated Guarantee of Protection
Even if you have several pregnancies and breastfeed each baby, you may still develop breast cancer. Having breast tissue alone puts you at risk of breast disease. Keep doing your monthly breast self exam to check for changes in your breasts. Be aware of benign lumps that can occur, such as a plugged milk duct, cyst, abscess, or fibroadenoma.
American Cancer Society. Overview: Breast Cancer - What Causes Breast Cancer? Last Updated: 09/26/2006. Breast Cancer Risk and Lifestyles
U.S. Food and Drug Administration. Breast-Feeding Best Bet for Babies
Breakthrough Breast Cancer.org. About Breast Cancer - Prevention and Early Detection - Breastfeeding. Breastfeeding for at least one year during your life may modestly reduce your risk of breast cancer.