Have you ever wondered why some people age better than others?

We all know someone who looks great for their age, and is also in robust health. And yet someone else who is exactly the same age might look older, and may be living with an age-related illness.

Chronological age is not always be a good indicator of how well someone is maturing. So, if our skin - which is our largest organ - suggests how well, or badly, we're aging, then the state of our other organs and the systems that keep them running may also indicate how old we are.

This measure is called your biological age.

And there are many ways of measuring biological age, from the simple - the strength of your hand grip, to the detailed - looking at the changes in chemical markers attached to your DNA, called epigenetic markers.

They lie "on top of" the DNA, without changing it - much like an instruction written on a post-it note attached to a piece of sheet music. The instruction means the music can be expressed differently, without changing the tune. Epigenetics explains why the DNA in every one of our cells is the same, and yet the cells can look very different from one another. They can be heart cells, blood cells, hair cells and so on, because the markers cause different genes on the same DNA to be expressed.

Epigenetics has allowed scientists to create clocks to tell you your biological age: the latest one can even tell you how fast you're aging. Advances in epigenetics have led to the new science of cellular regeneration.

And the world's first clinical trials are underway in the USA for a treatment that transforms old, dysfunctional and damaged cells into young healthy ones - treating aging itself.

Presenter: Ben Ansell

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