A drug to fight ageing may finally be on the horizon after the first trial in humans showed 'impressive' results.

For many years scientists have known that an accumulation of senescent cells in the body is linked to ageing symptoms such as frailty and arthritis, as well as diseases such as Alzheimer's and Parkinson's.

Senescent cells - also known as zombie cells - are not completely dead so are not cleared out by the body, but are too damaged to repair tissue or carry out normal functions. Unable to repair itself or clear out the waste, the body gradually deteriorates.

Previously animal studies have shown that removing these cells reverses the ageing process, extends lifespan, and restores lost youth.

Now for the first time scientists in the US have shown improvements in humans using a drug that sweeps away the defunct cells.

Although the initial three-week trial on 14 pensioners was only designed to show the drug was safe, the participants were able to walk faster, get up from a chair more quickly and scored better in ability tests.   

Senior study author Dr James Kirkland, of the Mayo Clinic, Minnesota, one of the world's best anti-ageing research centres, said: "This is like a glimmer that it might actually work. The results were impressive. All 14 got better in their functional ability.