A pill that alleviates the worst aspects of ageing could be closer than we think, an expert says.

In fact, a drug already licensed to treat cancer is getting the results scientists are after, in animals.

Professor Dame Linda Partridge, the director of the Institute of Ageing at University College London, said that when mice were fed the drug rapamycin, they lived longer, the Age reported.

But the drug also offered protection against neurodegenerative diseases, which are closely linked to ageing.

"Ageing is the main risk factor for all these horrible killer and chronic conditions dementia, cardiovascular disease, cancer," Professor Partridge said.

"What we are trying to do here is hit the underlying ageing process itself through understanding mechanisms to protect against all these things at once, rather than treating them piecemeal.

"Rapamycin is beginning to look like a proof of principle that that kind of approach is going to work.

However, the drug a natural product initially discovered in the soil of Easter Island is also believed to have a downside.

It's an immune suppressant and is also used to prevent the body rejecting an organ after transplant.

But there's potential to boost the drug's health benefits while minimising its undesirable side-effects, Professor Partridge said.

Professor Partridge will deliver the 2012 Graeme Clark Oration in Melbourne tomorrow.