Sad statistics – industrialization has reduced the number of children in the family. Every year, many developed countries report falling or negative population growth due to the rapid decline in the number of children born each year. At the same time, a group of researchers from the University of Bristol, the University of Oslo and the University of Queensland found that carrying a child protects the lining of the uterus from endometrial cancer (EC).
Scientists reported this in the journal BMC Medicine on November 1, 2022.
About endometrial cancer
Endometrial cancer ranks sixth in the world among cases of female oncology and is a deadly disease. Women in low-income countries are most at risk, with hundreds of thousands of lives lost to this type of cancer every year.
Previous studies confirmed: the development of endometrial malignancies is influenced by processes related to the reproductive function of women. Namely, ovulation and pregnancy. So, scientists considered the hormonal nature of EC, since in women who used only estrogen during the menopausal transition, the risk of endometrial cancer increased. At the same time, in women who also took progesterone as part of Hormone Replacement Therapy (HRT), these risks were reduced.
Plus, combined oral contraceptives (COCs), containing estrogen and progesterone (the pregnancy hormone), have been shown to reduce the likelihood of EC. And this protective feature increases over time. Moreover, pregnancy that ended in abortion or miscarriage provides even greater protection against endometrial cancer than COCs.
Another risk factor for endometrial cancer is an excessive Body Mass Index (BMI). This factor is most important for menopausal women and is also associated with hormonal changes.
The purpose of the study
So, scientists decided to investigate how the reproductive period, the number of babies born and the age of the last birth, correlate with the risk of endometrial cancer. And if a link is found, to determine whether it is causal.
The researchers used data from the UK Biobank (UKBB), which has information on more than 270,000 women. Only white European women were included in the study.
The scientists conducted multivariate analyses to find out the association between the number of live births, age at last birth, years of ovulation and other related aspects like age at natural menopause, age at menarche and BMI.
The scientists also used the Mendelian randomization (MR) method to assess the potential for causality. Here, genetic variants determine the causal relationship between exposure and outcome.
Findings of the study on endometrial cancer
The results included hundreds of genetic variants. Still, the analysis demonstrated that the risk of endometrial cancer is inversely proportional to the number of live births. Women who had given birth to three children had half the risk of developing EC than those who had not. Women with a longer reproductive period had a higher risk of endometrial cancer.
Incomplete pregnancies, i.e. miscarriages or abortions, also reduce the risk of EC, but less compared to full-term pregnancies.