One would expect that each time a women carries a baby that the stress and depletion would speed up the aging process and shorten her life. At Simon Fraser University, health sciences professor Pablo Nepomnaschy and postdoctoral researcher Cindy Barha followed a group of 75 Kaqchikel Mayan women over a 13 year period. They discovered just the opposite of what they expected to find. The women who had more children had longer telomeres which is associated with a longer life span and a slower aging process. While it is true that pregnant women receive higher social support and experience an increase in the actions of the gonadal steroid estradiol, which increases during pregnancy those do not seem to offer a sufficient explanation. By combining this study with information that has been discovered from several others we have an interesting answer to the mystery.
An article published in Scientific American during December 2012 holds the key. When a mother is carrying a baby they are connected by the placenta. It acts as a conduit to carry nutrients, oxygen, wastes and other substances between the mother and the fetus. This has been known for a long time. What is new is the discovery that stem cells from the fetus also travel through the placenta passing from the unborn baby back into the mother. They implant in the mother and can live for decades in the brain, lung, thyroid, muscle, liver, heart, kidney, skin and other organs. There is even evidence that if the mother has an internal injury that some of the stem cells from her child may repair the damage. Young stem cells are very powerful for healing and especially appropriate for a mother because half of their genetic material came from her. Not only does a mother carry in her body cells of all her children, but the younger children may carry cells that traveled from the fetus to the mother and then into a different child later on. So oddly enough many women and even some men carry cells in their body that is partly from their children or siblings.
Very young stem cells are powerful and that is basically what a mother is receiving each time she carries a baby. No wonder women who have more children age at a slower rate.
Cindy K. Barha, Courtney W. Hanna, Katrina G. Salvante, Samantha L. Wilson, Wendy P. Robinson, Rachel M. Altman, Pablo A. Nepomnaschy. Number of Children and Telomere Length in Women: A Prospective, Longitudinal Evaluation. PLOS ONE, 2016; 11 (1): e0146424 DOI: 10.1371/journal.pone.0146424