Asked by: Aaron Hacon, Norwich
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.