Do we get a new body every 7 years?

For this week's mythconception, Izzie Clarke has been picking apart the myth that we get a whole new body on a cellular level every 7 years...

Izzie - You may have heard that we get a whole new body on a cellular level every seven years. A fresh start? Yes please! Who cares how much you drank in your 20s, before long you’ll have a whole body with new cells and the damage should be written off - right? Wrong.

Your cells are the fundamental building blocks of your body. You have about 37 trillion of them and around 200 different types. The cells on the inner lens of your eyes have been there since you were a foetus, and the neurons on the outer layer of your brain, which plays a key role in memory, attention, and language to name a few, are never replaced.

However, some cells in other parts of your body do regrow. Your skin cells, for example, refresh every two to three weeks, whilst the cells that line your gut are constantly bombarded with acidic gastric juices so don’t last more than three days.

But how did we find out how long cells actually last in our body? The atmosphere naturally contains low levels of a radioactive form of carbon called carbon-14. But during the mid 1950s and early 1960s nuclear weapon tests released large amounts of additional carbon-14 into the atmosphere where it combined with oxygen to form carbon dioxide. Plants have been taking this in, we then eat the animals that eat the plants and hey presto… this radioactive carbon-14 has worked it’s way into the DNA of our cells too.

And because it happened at a very specific point in history, and we know how the levels of carbon-14 in the air have been changing since, scientists in Sweden have been able to use this so-called ‘carbon-14 bomb bump’ to work out how old the cells in different parts of our bodies are. Because cells that are being replaced will have new DNA and, hence, a more recent carbon-14 fingerprint than a cell made longer ago.

The scientists in Sweden found that the average cells in the intestines of an adult in their thirties were about 10 years old, and skeletal muscle cells were about 15 years old showing they’d been replaced several times since those individuals were born. The same tests carried out on brain cells, though, showed that they were as old as the individual, so they weren’t being replaced and if you lose them you won’t get them back.

So there we have it... while some cells do replace themselves over time, you’re pretty much stuck with the body you’ve got. So look after it.