Having boys seems better for cognition than having girls

Findings from previous studies suggest that there is a link between male microchimerism of foetal origin, when cells of a foetus cross the placenta and remain imbedded for decades in tissues of the mother, and maternal long-term health outcomes. Furthermore, one study has found a lower occurrence of male microchimerism in patients with Alzheimer´s disease compared to those with no neurological disorder. However, these studies have a major
limitation as they did not take into account social factors that are related to parenthood. If the effect of male microchimerism was due to socioeconomic benefits of parenting sons, it would be shared among mothers and fathers.

To add evidence to these observations, our group studied the relationship between cognitive functions and offspring sex using data obtained from both mothers and fathers who are enrolled in the Health and Retirement Study, a large longitudinal research project that collects detailed information about demographics, health-related factors and socioeconomic circumstances of US older adults. The lead author Dr. Katrin Wolfova presented the preliminary results of our study at the 21 st WPA World Congress of Psychiatry which took place online on October 18-21, 2021. Together with colleagues at the Columbia University, we tested a hypothesis that mothers of at least one boy would have better cognition than mothers with no boys, and that there would be no differences in fathers.

We found that having at least one boy was related to higher cognitive functions in both mothers and fathers, but this effect remained significant only in fathers after controlling for socioeconomic factors. We think that our results suggest that this effect might be driven by social factors rather than underlying biological mechanisms. One explanation for this difference in cognition between mothers of at least one boy versus mothers of no boys could be the Trivers-Willard hypothesis, which says that females in good condition have a higher likelihood of having a boy than females in poor conditions. Thus, when socioeconomic factors are taken into account, we don’t see any difference in cognition.

Another explanation for the observed differences might be that the parenting experiences are sex-specific. For example, previous studies show that fathers of boys invest more time into parenting than fathers of girls. In addition, fathers of boys work longer hours and have higher hourly wage. All of these factors might in turn contribute to higher cognitive stimulation throughout the whole life course and protect cognitive functioning in later life. 

We think that any effect of having boys, or not having boys, will be of greater relevance to younger birth cohorts, because there is a decline in the average number of children, and higher proportion of parents end up with only one child or two children, higher shares will have only female or only male offspring. In the next step, we plan to explore whether our results are affected by differences in mortality. To avoid a problem of bias due to non-random dropout from a study, we will utilize a joint modelling approach.

Created: 28. 10. 2021 / Modified: 28. 10. 2021 / Responsible person: MUDr. Pavla Čermáková, Ph.D.