The plight of nuns: hazards of nulliparity.

Catholic nuns are committed to leading a celibate, spiritual life in a monastery or convent. In 1713, Italian physician Bernadino Ramazzini noted that nuns had an extremely high incidence of that “accursed pest”, breast cancer. Today, the world’s 94 790 nuns still pay a terrible price for their chastity because they have a greatly increased risk of breast, ovarian, and uterine cancers: the hazards of their nulliparity. Fraumeni and colleagues compiled data for cancer mortality rates in 31 658 Catholic nuns in the USA between 1900 and 1954, and showed that nuns had an increased probability of dying from breast, ovarian, and uterine cancer compared with the general population (fi gure). MacMahon and colleagues were the fi rst investigators to make a formal link with parity, showing, in 1970, that parous women had a decreased risk of breast cancer compared with nulliparous women. Parous women receive further protection if they have their fi rst child at a young age, bear more children, and if they breastfeed. These reproductive factors are now known also to protect against the risk of ovarian and endometrial cancer. Nulliparous women have a higher number of ovulatory menstrual cycles than do parous women because of the absence of pregnancy and lactation, and an increased number of cycles aff ects cancer risk. Epidemiological studies of breast cancer have directly linked number of menstrual cycles to cancer risk. Women experiencing menarche before age 12 years had a slightly higher risk of breast cancer than did those who were older than 15 at menarche. Similarly, the risk of breast cancer is increased by 17% for every 5-year delay in menopause. Bilateral oophorectomy before age 40 years led to a 45% reduced risk of breast cancer compared with women with a natural menopause at ages 50–54 years. The increased number of cycles between menarche and menopause also leads to increased risk of ovarian and uterine cancers. This fi nding has been best shown by Eaton and colleagues’ mathematical model, which used age at menarche, fi rst pregnancy and menopause, and use of oral contraceptives to predict incidence of a woman’s reproductive cancer. Findings from this model showed that the lifetime risk of reproductive cancers in modern American women was about 128 (breast), 21 (ovarian), and 287 (uterine) times that in women of similar age living in late Palaeolithic times. However, it is not known how to improve the health of breasts that do not need to lactate, ovaries that need not ovulate, and a uterus that does not need to menstruate. Two large epidemiological studies of the health eff ects of contraceptive pills have shown that the oral contraceptive pill signifi cantly decreases overall mortality rate, does not increase breast cancer risk, and signifi cantly reduces risk of both ovarian and uterine cancers. The