Scientists might be able to reverse process of ageing, a new study suggests.

Volunteers who were given a cocktail of drugs for a year actually “aged backwards”, losing an average of 2.5 years from their biological ages, according to the new study. The research showed that the marks on their genomes that represent their “epigenetic clock”, as well as their immune systems, actually improved despite the passing of time.

The scientists involved in the study were shocked by the results.

“I’d expected to see slowing down of the clock, but not a reversal,” researcher Steve Horvath from the University of California, Los Angeles told Nature, which first reported the findings. “That felt kind of futuristic.”

Scientists caution that the study was done with a very limited number of participants: only nine people took the drug cocktail, and there was no control group. But if it is confirmed by further research it could have huge impacts on healthcare, the treatment of disease and how people think about ageing.

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In the study, participants were given a growth hormone and two diabetes medications. Scientists then monitored the test subjects’ epigenetic clocks, to understand the effect on how they aged.

The epigenetic clock is measured by the body’s epigenome – a record of chemical changes to an organism’s DNA. As people age, chemical modifications or tags are added to people’s DNA, and those change throughout their lives, so by looking at those tags a person’s biological age can be measured.

Researchers had actually intended to look at how the growth hormone would change the tissue in the thymus gland, which helps with the body’s immune functions and sits in the chest. It normally shrinks after puberty but they hoped to see whether it could be pushed to regrow, by giving participants the growth hormone.

It was only as a secondary consideration that researchers then checked how the drugs changed their epigenetic clocks. The study had finished when the analysis began.

Professor Horvath then looked at four different measures of the epigenetic clock to understand the differing ages of each of the patients. And he found that every one of them had reversed significantly – so significantly that he is optimistic about the results, despite the limited number of participants.

Scientists now hope to test the same effects with more people, through a controlled study, and with different age groups, ethnicities and with women.

The changes could still be seen in the blood of six participants who provided samples long after the study finished.