Breastfeeding linked to lower risk of uterine cancer

An international study has found that women who have breastfed at least one child have a lower risk of cancer of the uterus.

The study, which was led by QIMR Berghofer Medical Research Institute, is the largest and most comprehensive to be conducted into the link between breastfeeding and uterine cancer. The findings have been published in the journal Obstetrics and Gynecology.

Cancer of the uterus (also known as endometrial cancer) is the fifth most common cancer in Australian women. Rates have been increasing over recent decades. Cancer Australia estimates that nearly 2,900 new cases will be diagnosed in 2017.

The head of QIMR Berghofer’s Cancer Causes and Care Group, Dr Susan Jordan, and her colleagues examined data from more than 26,000 women with at least one child, including nearly 9,000 women with uterine cancer.

“We looked at the total amount of time these women had spent breastfeeding over the course of their lives,” Dr Jordan said.

“We found that women who had ever breastfed had an 11 per cent lower risk of developing uterine cancer than women who had never breastfed.”

The researchers also looked at how long the women had breastfed individual children for.

“We found that the longer women breastfed each child, the more their risk of uterine cancer reduced, up until about nine months when the reduction in risk plateaued,” Dr Jordan said.

“When women breastfed for between three and six months, their risk dropped by about seven per cent per child compared to women with children who didn’t breastfeed. And when women breastfed for between six and nine months, their risk dropped by 11 per cent for each child they nursed.

“In other words, a woman who breastfed two children for nine months each had around a 22 per cent lower risk of uterine cancer than a woman who had never breastfed her children.”

Numerous studies have identified a link between breastfeeding and decreased risk of breast cancer. However, previous studies into the relationship between breastfeeding and uterine cancer have had conflicting and inconclusive findings.

“On the basis of this study, we can now confirm that there is a link between breastfeeding and decreased risk of uterine cancer,” Dr Jordan said.

“We can’t say that this is definitely a causal relationship. However, it is plausible that breastfeeding could directly reduce the risk by suppressing ovulation and reducing estrogen levels, and in turn reducing cell division in the lining of the uterus.

“It is important to point out that breastfeeding won’t guarantee that a woman won’t develop cancer of the uterus, and, conversely, not breastfeeding doesn’t mean a woman will get uterine cancer.

“However, this study strongly suggests that breastfeeding reduces a woman’s risk. It’s already well known that breast feeding has lots of great benefits for mums and their babies. This is just one more benefit to add to the list.

“For a whole range of reasons, some women are either unable to breastfeed, or struggle with breastfeeding. While it’s important not to put more pressure on these women, this study suggests that supporting women to breastfeed could help reduce the incidence of uterine cancer.”

The study involved collaborators from the United States, Europe and China.