Women who breast-feed their babies for the recommended six months may be lowering their own risk of developing endometrial cancer, a new study suggests.
In the analysis of data from 17 past studies, researchers found that women who had ever breast-fed their children were 11 percent less likely than women who had children but didn’t breast-feed to be diagnosed with endometrial cancer.
Longer breast-feeding seemed to further lower endometrial cancer risk, though there was little extra benefit past six to nine months of breast-feeding, the study team reports in Obstetrics and Gynecology.
“Cancer of the uterus is becoming more common, and we need to try to prevent it,” said lead author Susan Jordan of the QIMR Berghofer Medical Research Institute in Brisbane, Australia.
Endometrial cancer is the fourth-most-common cancer in women in high-income countries such as the United States, Canada and Australia, according to the International Agency for Research on Cancer.
“The more women know about the things they can do to reduce their risks of future cancer diagnoses, the better,” Jordan said by email. “Although this piece of evidence by itself may not convince women to breast-feed, it contributes to the overall picture of health gains that can come from breast-feeding.”
The World Health Organization recommends that women exclusively breast-feed for the first six months of their baby’s life, then continue breast-feeding even after beginning to introduce solid foods.
The researchers analyzed pooled data from studies participating in the Epidemiology of Endometrial Cancer Consortium, including 10 from the United States and others from Canada, Europe, China and Australia. They looked at more than 26,000 women who had ever had a child, whether they breast-fed, and for how long. This included about 9,000 women with endometrial cancer.
After accounting for other factors that can influence risk of endometrial cancer, including age, race, education, oral contraceptive use, menopausal status, years since last pregnancy and body mass index, researchers found that the apparent protective effect of breast-feeding remained.
Notably, the risk reduction linked to breast-feeding was 28 percent among women born after 1950 but negligible among those born before 1950, which may reflect differences in breast-feeding practices, the study authors note. In the United States in the 1950s and 1960s, for example, breast-feeding rates were much lower than in recent decades, the authors note.
The study doesn’t prove that breast-feeding helps to protect against endometrial cancer, but it’s plausible, the authors write, because the growth of this type of cancer is stimulated by estrogen, which is suppressed during breast-feeding.
“The message is not only relevant for women making decisions about breast-feeding but also for society to understand the benefits so we can support women to breast-feed for reasonably long periods of time,” Jordan said. “However, it’s not always possible for women to breast-feed, so it should also be noted that just because a woman chooses not to or can’t breast-feed, it doesn’t mean she’ll go on to develop cancer.”
“Breast-feeding seems to significantly reduce the risk, but further studies originating in other countries are required to assess the association,” said Lianlian Wang of the Fourth Affiliated Hospital of China Medical University in Shenyang, China, who was not involved with the study.
The most recent endometrial cancer report produced by the World Cancer Research Fund and the American Institute for Cancer Research in 2013 classified the evidence for a benefit from breast-feeding as “limited — no conclusion.”
Jordan and colleagues are working with international collaborators to investigate the effects of breast-feeding on ovarian cancer risk. They’re also researching other factors that may influence the risk of endometrial cancer, including specific medications.
“Breast-feeding has consistently been found to be associated with reduced risk of breast cancer,” Jordan pointed out. “This provides evidence of another long-term health benefit for women who breast-feed for more than six months.”