Does pregnancy make you age faster?
You might joke that the kids are turning your hair gray, but does pregnancy and childbirth really have an affect on aging? It’s a question researchers have studied for years, with mixed results. Here’s what the science says about the effect of pregnancy on life expectancy.
How genetics and lifestyle affect aging
On average, women live about five years longer than men. There are lots of reasons for this, mostly to do with lifestyle and genetic risk for certain conditions. Men are more likely to die in car accidents, commit suicide, or develop cancer, for example. Often, genetics and lifestyle go hand-in-hand. Your genetics might determine if you’ll develop lung cancer from smoking, but your lifestyle is what puts you at increased risk to begin with.
Having children, and how many, is a lifestyle decision. But the effects of pregnancy and childbirth are often closely related to your genetics. A study from the UK found that heart failure was the most common cause of maternal death. But those women typically had underlying genetic factors that put them at higher risk. Some women are advised not to get pregnant if they have certain illnesses, because of the risk of medical complications.
We need to take both lifestyle and genetic factors into account when looking at the science behind pregnancy and longevity. Some studies show that women who never get pregnant have accelerated signs of aging. Does that mean pregnancy makes you younger, or does that mean many of the women who didn’t get pregnant had other medical conditions already?
Polycystic ovary syndrome (PCOS) is a common cause of infertility. It’s caused by a hormone imbalance that can affect the whole endocrine system. That’s why there’s a link between PCOS and diabetes, thyroid disorders, and autoimmune conditions. Women with PCOS are less likely to have children, or to have fewer children if they do conceive. They are also more likely to develop additional disorders later in life that can affect longevity. Yet in wider studies on the effect of pregnancy on life expectancy, these underlying conditions can often be overlooked. This leads to the mistaken conclusion that there is a direct link between pregnancy and longevity.
How pregnancy affects biological age
There are two common ways of calculating age — chronological and biological. Your chronological age is the number of years you’ve been alive. It’s the candles on your birthday cake! Your biological age is how fast or slowly you’ve aged at a cellular level. There are several different ways of calculating biological age, but the effects are all the same. If you have a higher biological age than chronological age, that means your body is aging faster than average. If your biological age is lower, your cells are younger than those of other people born at the same time as you.
The age of your cells is important because it affects your risk factor for age-related diseases and conditions. That can be anything from fine lines and wrinkles, to gray hair, hearing or vision loss, and even cancer.
One way to calculate biological age is to measure telomere length. Telomeres are like caps on the ends of your DNA strands. Every time your cells replicate, a tiny section of DNA gets shaved off. Telomeres protect DNA by getting cut down instead. The longer your telomeres are, the more replications your cells can perform before they start to damage your DNA. So people with longer telomeres live longer, because their cells stay healthier.
A study on telomere length after pregnancy found that women who had given birth had telomeres 4.2% shorter than women who had not given birth. While that doesn’t sound like a big difference, it is equivalent to about 11 years of aging at a cellular level. The post-pregnancy telomere shortening was even bigger than that caused by smoking (4.6 years) or obesity (8.8 years). The study also found that the more live births a woman had, the shorter her telomeres. This suggests that each pregnancy has a cumulative effect at accelerating aging.
How estrogen affects telomeres and aging
One major change that comes with pregnancy is increased estrogen production. This is the female sex hormone, and it’s important for creating new blood vessels to take nutrients to the growing baby. However, studies on the Effects of estrogen on breast cancer development have found a link between higher levels of estrogen exposure and breast cancer.
More pregnancies means more estrogen production. It makes sense that multiple births can increase the risk of breast cancer. However research has found that isn’t the case. In fact, the breast cancer risk is 12% lower for women who have had multiple pregnancies. One reason for this might be that during pregnancy, menstruation stops. This prevents the usual estrogen fluctuations that come with having periods. Over a pregnancy, the extra estrogen produced is still less than would be produced during nine or ten monthly cycles.
This means that multiple births can increase longevity by reducing the overall risk of certain cancers. This isn’t because the pregnancy is beneficial to the body, but because it pauses other bodily functions which are more harmful.
Just because estrogen exposure increases the risk of some cancers, doesn’t mean it’s all bad. One positive side-effect of estrogen exposure is longer telomeres. Estrogen helps to activate the protein that telomeres are made from. This could be one reason why women have longer telomeres, and live longer, than men.
We know that during pregnancy, women produce more estrogen. However the extra amount is still not as much as women would produce over 9-10 menstrual cycles. That means each pregnancy reduces the amount of estrogen exposure a woman gets over her lifetime.
Several studies back this up. One looked at the relationship between years of menstruation and longevity. Basically, the earlier a woman starts menstruating, and the later she reaches menopause, the more estrogen exposure she has. This leads to longer telomeres and therefore longer lifespan. A second study, on reproductive history and telomere length, found that the more children a woman had, the shorter her telomeres were. That fits with what we know about pregnancy reducing your overall estrogen exposure.
How pregnancy increases oxidative stress
The third key effect of estrogen is to reduce oxidative stress. Oxidative stress is when too many unstable molecules — called Reactive Oxygen Species, or ROS — start to build up in your system. They destabilize surrounding cells, and can even damage DNA. When the damage gets out of control, it can cause widespread harm. This results in everything from cells shutting down to cancer-causing mutations.
A key source of these unstable molecules is through our mitochondria. As our cells convert food into energy, ROS are a by-product. During pregnancy, metabolism increases dramatically, and that means more ROS get produced. The double-effect of higher ROS production, plus less ROS-fighting estrogen, results in increased damage at a cellular level.
Other ways pregnancy harms the body
Growing a whole other person inside you has other negative effects for the body. During the third trimester, when the baby’s skeleton is forming, the fetus depletes the mother’s calcium levels. If she doesn’t have enough calcium, it will take it from her bones. Calcium deficiency in pregnancy can result in long term damage and increased risk of osteoporosis, a brittle bone condition.
Being pregnant also affects the immune system. Your white blood cells work by attacking anything inside your body that isn’t part of you — that doesn’t match your DNA. Babies have their own DNA, and while it’s similar to the mother’s, it isn’t the same. That means the baby is at risk from the mother’s own immune response. To prevent this, the immune system changes and becomes less effective. This leaves the mother at increased risk of certain infections during pregnancy. This includes viruses such as influenza, hepatitis E, and herpes simplex, and parasites like malaria.
Finally, pregnancy is hard on your heart. The average pregnancy increases blood volume by 45%, although it can be as much as 100%. The heart has to work much harder as a result. This increased strain is one reason why heart failure is a leading cause of maternal death. Women with underlying heart conditions are most at risk because of the extra work their hearts have to do.
Can pregnancy help you live longer?
While all of that sounds like pregnancy is terrible for the body and reduces longevity, the science isn’t so black and white. After all, if pregnancy was nothing but harmful, women who had many children would have very short lives. However there’s no direct relationship between the number of live births a woman has and how long she will live. In fact, there’s some evidence to suggest that having children can help women to live longer.
One study found a relationship between a mother’s age at the birth of her last child and her longevity. Women who had their last child after 33 were twice as likely to live to the top fifth percentile as women who had their last child before 29. Women who had a child after 40 were four times more likely to live to 100 than women who stopped having children earlier.
Like with the statistics about women who don’t have children having a shorter life expectancy, there is some underlying cause and effect at play in these figures. Older mothers tend to be healthier than the average women their age, making it more likely they would live longer lives regardless if they became pregnant.
However researchers did find a U-shaped relationship between pregnancy and longevity. Women who had 0-2 or 5-7 live births aged faster than women who had 3-4 live births. This suggests pregnancy does have a positive effect on aging — to a point.
Source: Shirazi, T.N., Hastings, W.J., Rosinger, A.Y. et al. Parity predicts biological age acceleration in post-menopausal, but not pre-menopausal, women. Sci Rep 10, 20522 (2020). https://doi.org/10.1038/s41598-020-77082-2
In the above charts, researchers measured four different cellular aging markers. The results are shown for premenopausal women (in orange) and postmenopausal (in blue). A zero score means that measurement was average for women of the same age. A lower score means aging slower, while a high score means aging faster. In postmenopausal women, those who had 3-4 live births scored the lowest on every aging marker. That means that after menopause, those women aged slower than other women their age.
The results after menopause are very different to those from women before menopause. This suggests that the effects of pregnancy on longevity can only really be seen as women begin to enter old age. Scientists think that during their most fertile years, women’s bodies compensate for the negative effects of pregnancy to keep reproducing. That’s why women who have 5-7 live births scored the lowest for signs of aging before the menopause, but are among the highest afterward.
Women who had zero live births scored among the highest for signs of aging both before and after the menopause. There are probably several causes for this. One is likely to be underlying medical conditions that stop women from reproducing. However another reason is likely to be that pregnancy does help to slow down aging.
There is no simple yes/no answer to whether or not pregnancy can shorten or increase longevity. Both aging and pregnancy are complicated bodily processes, with a huge number of variable factors. There is some scientific evidence that having 3-4 live births can be beneficial to the mother’s longevity. However it’s also important to consider other health factors that may explain a higher or lower number of births and also have a separate impact on longevity.
Socioeconomic factors also affect aging, but are harder to identify through biological analysis. Women who have several children are likely to have a better social support network in old age. This can help them to live longer than women who don’t have that network. Either zero or multiple pregnancies could suggest women have a lower income and less reliable access to medical care. Both of these socioeconomic factors can reduce life expectancy.
One consideration is that pregnancy might help you age healthier. Reduced exposure to estrogen might lead to shorter telomeres, but it also reduces the risk of developing certain cancers. And a study by the Alzheimer’s Association found that women “with three or more children had a 12 percent lower risk of dementia compared to women with one child.”
Finally, there’s the outcome of pregnancy to consider — the child. No matter how much stress kids cause, research shows that parents live longer than non-parents. While science shows mixed results about the impact of pregnancy on longevity, rearing children and building an intergenerational family unit consistently improves your chances of living a longer, healthier life.