Are cells in your body really only 10 years old?

Chris Smith debunked this commonly repeated myth... Chris - Well it's definitely not true because actually your brain cells - you are born with those brain cells - they're formed as you're developing and they have to last you a lifetime and that's why we get neurodegenerative diseases when you lose brain cells. Also, there are other cells in things like your retina, which is part of your brain, those photoreceptors have to last you a lifetime. Muscle cells are only very slow at replacing themselves, for instance, cardiac muscle in your heart is only very, very slowly turning over, if at all, so that muscle has to last a lifetime. But, some cells, including fat cells, do last about twelve years and we know this because someone wrote to us at the Naked Scientists a little while ago and they said "can I carbon date my gran?" And this is someone from South Africa who said their grandma didn't know how old she was because she'd never been told the date of her birth. They were intrigued to find out how old she really was because they said she really is very old indeed - can we find out? And, in fact, there's a lady Kirsty Spalding at the Karolinska Institute in Sweden and she did some studies where they have done carbon dating of fat cells and you can use DNA for this because the DNA incorporates atmospheric carbon, which has got a carbon 14 radioactive signature in it and we know what the radioactive signature is doping over time. So we can use that as an index of age and they found that fat cells last about twelve years and then they sort of disappear and you replace them with new ones.