Family size and cardiovascular health
A strong positive correlation between number of children and risk of developing cardiovascular disease in women has been known - at least within the medical community - for decades. This was assumed by many to be due to the permanent changes that occur within a woman's body during pregnancy, which are compounded with multiple pregnancies. Some argued that socioeconomic factors also played a large role, with decreases in disposable income with increasing number of offspring for all but the very wealthiest, but epigenetic changes (permanent changes to chromosomes) from multiple pregnancies weakening the cardiovascular system was still a very dominant theory.
Just as much of science has overlooked women (and if you regularly read sports research journals, you'll know only too well that they still do. Study participants are invariably white or African-American young males), this particular area of research overlooked men. Given that it was examining the relationship between pregnancy and cardiovascular risk, this is unsurprising, until you recall that good science seeks to disprove a hypothesis. Only when all other possibilities are exhausted, can it finally be accepted.
Recently, researchers finally began to look at men - and lo and behold, there was the exact same correlation between number of children and future development of cardiovascular complications. Sacré bleu!
Despite a strong correlation now being demonstrated in both women and men between number of children and cardiovascular risk, the relationship is clearly still a very complex one, and not necessarily causative. Whilst it is true that a greater number of children may reduce disposable income and result in lifestyle changes potentially (yet contentiously) unconductive to cardiovascular health, it may also be true that those already economically less advantaged or already practicing poorer lifestyle and dietary choices, may be simultaneously more likely to have larger families.
One potentially confounding factor is that childless individuals are even more at risk from developing cardiovascular disease than those with multiple offspring, but in this instance, it is very difficult to separate those who are childless by choice from those who may be suffering from medical conditions which make it impossible to support a child (through pregnancy or adoption).
Is there a correlation between number of children and the development of cardiovascular disease? Clearly, yes. Is there causation? The link is no longer so clear cut.
Read more in the European Heart Journal: Peters, S. & Regitz-Zarosek, V. (2017). Pregnancy and risk of cardiovascular disease: is the relationship due to childbearing or childrearing?