Longevity Briefs: Does Pregnancy Make You Age Faster?

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Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

The problem:

There’s a well established relationship between fertility and ageing. Species that reproduce earlier and have more offspring also tend to have shorter lifespans. This is probably an evolutionary trade-off: by investing more energy into reproduction, an organism has less energy to repair age-related damage, but gets more opportunities to pass on its genes to the next generation before it dies of disease or predation. Yet this relationship seems to hold true within species, including humans. Studies show that women who are more fertile tend to get more age-related diseases and live shorter lives on average, suggesting that reproduction could perhaps accelerate ageing.

One problem with this line of thinking is that the outcome is very far removed from the variable of interest. The average woman has her first child in her 20s and dies in her 80s – that’s a large span of time during which confounding factors could interfere with the relationship between fertility and mortality. Things like the financial and social constraints of having more children or career disruptions are not easy to control for. One way around this is to measure this relationship in young people using biomarkers that approximate how quickly someone is ageing. If younger people with more children are already ageing faster, the relationship between fertility and ageing is more likely to be a direct one.

The discovery:

In this study, researchers looked at blood samples from 1735 young people in the Philippines. These were both men and women born in 1983 and were about 21 years old at time of their first blood sample. New blood samples were taken again for some participants 4-8 years later.

The researchers used 6 different epigenetic clocks to estimate how quickly participants were ageing. Epigenetic clocks are algorithms that estimate one’s true biological age based on molecular changes to the DNA molecule throughout life. They found that at the time of the first measurement, women who had been pregnant at least once were biologically older according to all 6 clocks when compared to those who had not been pregnant (after controlling for confounding factors like socioeconomic status). This was equivalent to between 4 and 14 months of accelerated ageing, depending on the clock. A greater number of pregnancies at the time of the first blood sample was also associated with greater biological age. Furthermore, a greater number of pregnancies between the first and second blood samples was associated with faster biological ageing during this period, but only according to two of the six clocks.

Rate of ageing according to six epigenetic clocks at the time of the first blood sample, according to gravidity (number of pregnancies). Each dot represents one participant. Higher values represent higher rates of ageing, except in the case of the DNAmTL clock, for which lower values represent a faster rate of ageing. Note that it’s perfectly possible to have had 3+ pregnancies, yet still be ageing slower than someone who has had none. On average, however, more pregnancies correlates with faster ageing.
Pregnancy is linked to faster epigenetic aging in young women

In the case of the male participants of the study, there was no significant relationship between biological age and the number of pregnancies fathered.

The implications:

There is a strong link between lower socioeconomic status, poorer education, and increased likelihood of pregnancy earlier in life. However, this study controlled for these factors, and the fact that men who fathered more pregnancies did not age faster suggests that there is something about the biological process of pregnancy (or perhaps breastfeeding) that accelerates ageing. Such controls aren’t perfect, though. A tendency for women to take on more parental responsibilities, a higher probability of post-natal depression, and other factors related to pregnancy could have contributed to the faster pace of ageing.

It’s also important to keep in mind that the participants were only 21 years old at the time of the first blood test. Many of them had their first child during late adolescence when pregnancy complications are more likely. In other words, they aren’t a representative sample, and pregnancies that occurred during the subsequent decade only accelerated ageing according to two of six epigenetic clocks. Finally, we do not know whether the faster pace of epigenetic ageing shown in this study actually translates into worse health outcomes later in life. With all that being said, the findings of this study do line up with our theories about a trade-off between reproductive effort and healthy ageing.