A US clinical study has offered a tantalising glimpse at a future where humans can control the ageing process, showing for the first time that we might be able to wind back our biological clocks.

The study saw nine healthy people monitored over the course of a year as they took a cocktail of three common drugs - two diabetes medications and a growth hormone.

By measuring marks on the test subject's genomes, scientists found that the participants took 2.5 years off their biological ages on average and also showed signs that their immune systems were rejuvenated.

Researchers have sounded a note of caution over the stunning results, however, telling noted scientific journal Nature that the findings are preliminary because of the small trial size and the lack of a control.

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Geneticist Steve Horvath at the University of California, who conducted the epigenetic analysis, said: "I'd expected to see slowing down of the clock, but not a reversal, that felt kind of futuristic".

German cell biologist Wolfgang Wagner told Nature: "It may be that there is an effect, but the results are not rock solid because the study is very small and not well controlled."

Horvath told the UK's Daily Star that he was surprised by the findings: "I did not think it was possible to find age reversal.

"Our study suggests a cocktail of relatively safe substances can achieve a ­distant dream from science fiction novels."

We might yet be able to turn back the clock. Photo / 123RF
We might yet be able to turn back the clock. Photo / 123RF

The researchers stumbled across the age-defying properties of the medications while trying to stimulate the thymus gland, which is responsible for turning immune cells into specialist cells that destroy invading pathogens.

The gland begins to lose function after puberty, but studies have suggested that growth hormone can kickstart the process.

Immunologist Gregory Fahy conducted a study into use of growth hormone and decided to check on the effects on the body's epigenetic clock after the study had finished.

Fahy approached Horvath to analyse the patients' biological age and it was then that the reversal was discovered.

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Horvath told Nature that the effect persisted in the six participants who provided a final blood sample six months after the trial ended.

"Because we could follow the changes within each individual, and because the effect was so very strong in each of them, I am optimistic," he said.

The study isn't the only effort being made to increase the human lifespan.

Kiwi Laura Deming has dedicated her career to finding ways to slow down ageing.

"Most people think of the body as something that breaks down over time and is unfixable, similar to a car rusting," she told the Daily Mail.

"But there are some cars that have been around since 1910 because people are maintaining them and replacing the parts. Our goal, eventually, is to be able to do that with the human body."

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She's now leading her own $39m Longevity Fund that supports entrepreneurs developing therapies for age-related diseases.