Reproductive factors

Reproductive factors associated with an increased risk of endometrial cancer risk include being younger when periods start and being older at menopause. 

Some reproductive factors may protect against developing endometrial cancer. This includes having children and breastfeeding.

Age at menopause

Later age at menopause* is associated with an increased risk of endometrial cancer.

The average age of menopause in Australia is 51 years. The risk of endometrial cancer increases by around 6% for every year older a woman is at menopause. For example, a woman who goes through menopause at the age of 55 years has about a 26% higher risk of endometrial cancer than a woman who  goes through menopause at age 51 years. Conversely, a woman who goes through menopause at a younger age has a decreased risk of endometrial cancer.

The increased risk of endometrial cancer in women who are older at menopause is likely to be due to hormones. When menopause occurs at a later age, the body is exposed to the female hormone oestrogen for longer. Longer exposure to oestrogen over a woman’s lifetime can increase the risk of endometrial cancer.

The increased risk may also be due to lower levels of the female hormone progesterone in women who are closer to menopause. Progesterone can reduce the effects of oestrogen on endometrial cells. If progesterone levels are lower, the effects of oestrogen are stronger, meaning that the risk of endometrial cancer can increase.

*Menopause occurs when 12 months have passed since a woman’s last menstrual period.

Age when periods started

Starting menstrual periods at a younger age is associated with an increased risk of endometrial cancer.

The earlier a woman’s periods start, the higher her risk of endometrial cancer. The risk increases by about 2% with each year younger a woman is when she starts having periods. For example, the risk of endometrial cancer in a woman who has her first period at age 11 is about 4% higher than for a woman who has her first period at age 13.

The increased risk of endometrial cancer in women whose periods start at a younger age is likely to be due to hormones. Women whose periods start earlier are exposed to the female hormone oestrogen for longer than women whose periods start at an older age. Starting periods at an older age reduces the number of menstrual cycles a women experiences during her lifetime and therefore her risk of endometrial cancer.

Breastfeeding

Breastfeeding is probably associated with a decreased risk of endometrial cancer.

The longer a woman breastfeeds, the lower her risk of endometrial cancer. The risk of endometrial cancer decreases by about 3% for every 3 months a woman breastfeeds.

The protective effect of breastfeeding is likely to be due to hormonal changes. When a woman is producing milk and breastfeeding, the level of the female hormone oestrogen in her body is lower. This slows the growth of endometrial cells and can reduce the risk of endometrial cancer.

Having children

Having children is associated with a decreased risk of endometrial cancer. 

The risk of endometrial cancer is about 25% lower in women who have one child compared with those who have never had children. The risk of endometrial cancer decreases as the number of children that a woman has increases. For example, the risk of endometrial cancer in a woman with three children is about half that of a woman who has not had children. Conversely, not having children is associated with an increased risk of endometrial cancer compared with having children.

The association between having children and decreased risk of endometrial cancer is likely to be due to hormones. Studies suggest that the female hormone oestrogen is associated with risk of endometrial cancer. When a woman is pregnant, her usual menstrual cycle is interrupted. This reduces the length of time her body is exposed to oestrogen and this may lower her risk. Hormone changes during childbirth may also be involved. The physical process of childbirth may also lower the risk of endometrial cancer by removing cancer-causing cells from the endometrium during delivery.