Having more babies lowers risk of endometrial cancer

Researchers from The University of Queensland (UQ) have revealed having more babies reduces a woman’s risk of endometrial cancer, using genetic analysis to determine that having three babies compared to none could decrease a woman’s risk by 50%. Their research was published in the journal BMC Medicine.

Endometrial cancer occurs in the lining of the uterus and is the fifth most diagnosed cancer in Australian women, affecting one in 52. The researchers found that the more time a woman spent pregnant or on the contraceptive pill — when the body is exposed to less oestrogen — the lower her risk of endometrial cancer.

While previous studies have shown multiple pregnancies and using the pill can reduce the risk of endometrial cancer, this is believed to be the first study that used genetics to study multiple risk factors at once. In their analysis, the UQ researchers examined how many years women ovulated, calculated by subtracting time spent pregnant or taking the contraceptive pill from the years spent menstruating.

“It is thought that high levels of oestrogen, unopposed by progesterone, is a risk factor for developing endometrial cancer,” said UQ’s Dr Gunn-Helen Moen.

“Pregnancy and the contraceptive pill both provide progesterone to oppose oestrogen, and this could be why we see a protective effect against this cancer.

“To put it simply, the shorter the exposure to oestrogen over your lifetime, the smaller your risk of developing endometrial cancer.”

The researchers found evidence that suggested reducing years ovulating could reduce the risk of endometrial cancer, but the strongest links pointed to childbirth. Moen said there could be several explanations for why pregnancy reduces the risk of endometrial cancer.

“It could be the increase in protective progesterone in the latter stages of pregnancy, or it could be because the body potentially removes pre-cancerous endometrial cells from the uterus during birth,” she said.

The researchers separated some known risk factors for endometrial cancer, such as increased body mass index (BMI) and age at first menstruation and menopause, and looked specifically at the effect of the number of live births and years ovulating. Moen explained, “In obesity, high levels of oestrogen are produced in fat tissue, which makes it a risk factor for endometrial cancer.”

Endometrial cancer cases are increasing worldwide, and Moen said this may be due to rising BMI levels, which account for about 40% of endometrial cancer cases in developed countries. “But we wanted to find out more about the impacts of live births directly, irrespective of other known risk factors,” Moen said.

“We used data to study hundreds of genetic variants, six of which were associated with the number of live births.”

The result, Moen said, is that this study is the first time researchers have been able to establish a cause-and-effect relationship between the number of births and a reduced risk of developing endometrial cancer. That said, the team could not be sure if the same was true for years ovulating and oral contraceptive pill use.

“Analysing larger datasets could help us understand more clearly whether it is the hormonal or mechanical effects of pregnancy that give a more protective effect, as well as dig further into the effect of oral contraceptive pill use,” Moen said.

Image credit: iStock.com/romrodinka

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