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Long-Term Breastfeeding May Reduce Breast Cancer Risk

Long-term breastfeeding may reduce a woman’s risk of developing breast cancer by as much as 50%, according to a study recently published in the

American Journal of Epidemiology.

Breast cancer is the second leading cause of cancer death in women in the United States, with approximately 200,000 cases diagnosed each year. Although several risk factors have been associated with breast cancer, the cause of the majority of cases of breast cancer remains unknown. As researchers continue to explore the causes of this disease, they also uncover factors that may prevent the development of breast cancer. Often, lifestyle changes and choices can help reduce the risk of cancer.

In a hospital-based study conducted in the Shandong Province in China, researchers evaluated and compared 404 women with breast cancer and 404 women without breast cancer. Through personal interviews, the researchers collected detailed information regarding lactation, menstruation and reproduction. They found a significant association between the duration of lactation and a reduced breast cancer risk.

The results of this study indicated that women who breastfed a child for more than two years had a 54% reduced risk of developing breast cancer, compared with women who breastfed for 6 months or less. In addition, the results indicated that women who had a lifetime duration of lactation anywhere from 73 to 108 months had a significantly lower risk of developing breast cancer. The risk was further decreased for women who breastfed for 109 or more months of their lives.

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The researchers concluded that prolonged lactation reduces the risk of breast cancer and found that both the duration of lactation per child and the lifetime duration of lactation were important factors. They speculated that specific breast cancer hormones might be suppressed during lactation, while protective compounds may be released.

The results of this study are promising, as the best treatment for cancer is preventing its occurrence in the first place. Cancer is largely a preventable illness, but awareness of the opportunity to prevent cancer through changes in lifestyle is often under-appreciated. Women who are interested in the prevention of breast cancer may wish to speak with their physicians about the risks and benefits of participating in clinical trials that evaluate the relationship between lifestyle factors and the development of cancer. Two sources of information about ongoing clinical trials include clinical trials listing services provided by the National Cancer Institute ( and also performs personalized clinical trial searches on behalf of patients. (Lawrence Livermore National Laboratory Press Release) (

American Journal of Epidmeiology, Vol 152, No. 12, pp. 1129-1135, 2000)

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