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What percentage of my body is the same as five years ago? © Getty Images

What percentage of my body is the same as five years ago?

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The idea that we replace every cell in our bodies every few years is a popular one – but incorrect nonetheless.

Asked by: Aaron Hacon, Norwich

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The idea that we replace every cell in our bodies every few years is a popular one – but incorrect nonetheless.

Fat cells are replaced at about 10 per cent per year, but heart muscle cells turn over at just 1 per cent per year at age 25, declining to 0.5 percent by age 70. Even if you live to be 100, you’ll still have more than half of the heart muscle cells you were born with. The neurones of the cerebral cortex and the cells in the lens of your eye are never normally replaced.

But even though the cells aren’t completely replaced, they still change. Molecules are continually exchanged with the environment during ordinary metabolic processes. The water in your body turns over at about 3 litres per day. An adult has around 40 litres of body water, so that’s 7.5 per cent per day. After two years, it’s statistically unlikely that you have any of the same water molecules. But the calcium in your teeth is locked up forever.


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Authors

luis villazon
Luis VillazonQ&A expert

Luis trained as a zoologist, but now works as a science and technology educator. In his spare time he builds 3D-printed robots, in the hope that he will be spared when the revolution inevitably comes.

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