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There may be a significant negative effect on kids if their mothers are older

grandparents with baby
Flickr/ devinf

American women are setting all sorts of records when it comes to having children later in life. But that might not be a great thing all around.

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Not only are older mothers prone to health issues during pregnancy, but their age could impact their childrens' lives, too, some scientists think.

The average age of a mother giving birth to her first child was 26 in 2013 — a record high, according to Centers for Disease Control and Prevention data, that includes plenty of women over 35 and even some over 40. A total of 677 women over 50 gave birth in 2013, more than ever before.

These records are impressive in part because a woman's fertility declines with age.

But while giving birth to a child is considered a happy ending when measuring a woman's ability to have kids, this birth is actually the beginning of a life that may be deeply affected by the mother's age at birth.

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Research has suggested that children born to older women are likely to have shorter lives. In a study of 200 years of demographic data about a large group of Swedes, mother's age at birth was one of the most significant non-external factors affecting how long a person lived, along with the mother's lifespan.

It's no shock the genes a mother passes down will affect her child's lifespan. But in addition to genes, mothers pass down a crucial cellular component called mitochondria. As Dr. Martin Wilding proposes in the journal Fertility and Sterility, published by the American Society for Reproductive Medicine, children born from older mothers could receive compromised mitochondria in their cells — shortening their lives.

A compromised powerhouse

mitochondria
Mitochondria, what keep the lights on. Wikimedia Commons/Sterilgutassistentin

Mitochondria are responsible for generating the energy individual cells need to function. They have a complicated origin story, which results in them having their own genomes, which work and copy themselves separately from the rest of a cell's DNA.

The process of generating energy forms dangerous by-products that can damage DNA, and mitochondria have limited abilities to repair damage to their genes. Because of this, mistakes accumulate in mitochondrial DNA over time, and these mistakes can make mitochondria not work as well.

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This isn't a problem in most cells of the body, which are frequently replaced throughout someone's lifespan. But by some quirk of nature, that's not how eggs work.

A woman is born with all the egg cells she will ever have, and they mature and are released for potential fertilization throughout her life.

When fertilized, an egg merges with sperm, and the resulting embryo inherits the mitochondria from the mother's much larger egg cell, not the father's tiny sperm, which only has a few (and paternal mitochondria rarely, if ever, enter the egg).

The mitochondria handed down to the fetus copy themselves and divide to populate every cell of the fetus, and eventually, the resulting child.

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It seems that as a woman ages the mitochondria in her egg cells accumulate more and more damage to their DNA, some of which could be handed down to the child. A 2014 study in the journal Proceedings of the National Academies of Sciences showed that children born to older women have more of these mistakes in their mitochondrial DNA than children born to younger women.

If that's the case, children that have inherited compromised mitochondrial DNA from older mothers might have mitochondria that don't work quite as well as they could, right from the beginning of their lives. Wilding suggests that children with more defective mitochondria would be less healthy and more likely to get sick, and thus won't live as long.

This theory linking mother's age, bad mitochondrial DNA, and child's lifespan would explain why the Swedish children born to older mothers had shorter lifespans, but it has yet to be proven experimentally.

Plus, the theory comes with the caveat that many things affect how long a person lives — from genetics to every little detail of environment. That makes it even harder to tease out exactly what effect mother's age has.

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But as more women delay having children, it's definitely worth considering and studying what unintended consequences the trend may have.

Innovation Medicine
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