How Often Do Our Bodies Replace Themselves?

We know that our bodies contain trillions of cells, and are constantly replacing old cells with new. Does that mean that all of our cells are replaced periodically? In other words, do we end up with a new body every few years?

According to the article “Does the Human Body Replace Itself Every 7 Years?” by Donavyn Coffey on the LiveScience website (https://www.livescience.com/33179-does-human-body-replace-cells-seven-years.html?), it’s not that simple.

Some cells are replaced very quickly. According to Olaf Bergmann, a principal researcher in the Department of Cell and Molecular Biology at the Karolinska Institute in Stockholm, Sweden, “Most of the skin and gut are replaced very fast, most likely within months.”

For others, the pace is slower. It takes three years to replace most liver cells. The heart takes even longer.  “The human heart renews at a rather low rate, with only 40% of all cardiomyocytes [the cells responsible for the contracting force in the heart] exchanged throughout life,” Bergmann has said. Skeletal-cell replacement needs about ten years to replicate a complete skeleton, according to the New York Times

The really bad news (especially for some people) is the brain. There is evidence that some neurons in the hippocampus renew, but only at a rate of 1.75% annually, as per a 2013 study in the scientific journal Cell. And some types of neurons within the striatum also regenerate, as per a 2014 study in Cell. But unfortunately other types of neurons stay with us for our entire lifetimes, according to Bergmann. And even the distinct cells that can rejuvenate are not replaced entirely, but only partly.

But still, if so many cells are being replaced, why do we still get old? That’s because of our “biological age,” which still reflects how our bodies respond to the passage of time. Even as organs renew their cells, they still age due to changes such as mutations, Bergmann said. As cells replicate, the DNA continually divides and copies, and mistakes are made over time. Mutations can thereby accumulate and affect the life of the cell and its genes.

So even if some cells in our bodies are replaced, our much-copied DNA means there is no escape from aging.

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