An expert in genetics revealed how to tell if you're ageing well - and the answer is all in your fingernails. 

Dr David Sinclair, a genetics professor at Harvard Medical School, revealed that fingernail growth could indicate whether your body is ageing slower or faster than your number of birthdays. 

The rate at which your nails grow could suggest how quickly your body generates new, healthy cells, which is more likely to protect your body against age-related decline.

Speaking on his podcast Lifespan, Dr Sinclair said: "The rate of your nail growth is a really good indicator of how you're ageing or not ageing."

In a 1979 study, scientists found that weekly fingernail growth slowed by about 0.5 percent per year from the age of 30, suggesting that nail growth is linked to ageing.

Referencing the study, Dr Sinclair said: "I do pay attention to whether my nails are slowing down in their growth or not. Every time I have to cut my nails, I'm thinking, how long ago did I cut my nails?"

If nails grow quickly and you need to cut them more often than other people your age, it could suggest your body is ageing slower than average.

The decline is thought to be linked to blood circulation slowing down as we age, meaning nails get fewer nutrients for growth.