Breast, ovarian and uterine cancers result from childlessness, say scientists.
Not having children is a risk factor for cancer because pregnancy, as well as breastfeeding a baby, reduces the number of ovulatory cycles a woman has in her lifetime. More ovulatory cycles increases cancer risk. Women who begin their periods at an early age and hit the menopause late also have a higher risk.
In the first half of the 20th century, scientists who studied nearly 32,000 Catholic nuns in the US established that their death rates from breast, ovarian and uterine cancer were higher than for other women of their age. In 1970, it was formally recognised that the lack of childbearing in nuns raised their breast cancer risk.