Number of children and death from hormone-dependent cancers

The association between number of children of current marriage reported by 431,604 women aged 45-74 years at the Norwegian Census in 1970 and mortality, at follow-up through 1985, from hormone-dependent cancers, i.e., cancers of breast, corpus uteri and ovary combined, has been investigated. The reduction in age-adjusted mortality was 9.6% (95% confidence interval; 8.3-10.9%) for each child with no deviation from linearity. Women with 8-11 children had a relative risk of 0.34 (0.25-0.47) compared to nullipara. Adjustment for age at first birth slightly changed the effect of number of children on mortality to 9.3% per child. The reduction in mortality per child was for cancer of the breast 7.2%, corpus uteri 12.2% and ovary 12.7%. Our findings indicate that having few children is a major risk factor for death from the 3 hormone-dependent cancers combined.