Sons May Be Bad for Maternal Health at Older Age: New Evidence for Costs of Reproduction in Humans.

High investment in reproductive processes at the expense of other physiological functions may result in poor maternal health. Health status at older age can be reliably assessed by self-rated health, which is a strong predictor of mortality. We investigated trade-offs between reproduction and health by analysing relationships between self-rated health and the total number of children ever born by a woman, and the number of her sons and daughters among 559 post-reproductive women aged 45-92 from Poland. The number of sons, but not the number of daughters or the total number of children, was significantly associated with self-rated health, adjusted to potential confounders (age, education, marital status, current smoking, and body mass index). Each son increased the odds of reporting poor health by 11% (odds ratio = 0.89; 95% confidence interval = 0.81-0.99). Sons are more energetically and immunologically demanding for the maternal organism which may explain why having sons has more negative influence on maternal health in older age than having daughters. In order to understand trade-offs between reproduction and maternal health not only the total number of children but also sex of the children should be taken into account.