Scientists at the Skolkovo Institute of Science and Technology in Russia say they have worked out the ultimate limit of the human lifespan, and it suggests people could one day live to be between 150 and 190 years old on average.
The researchers found that even if every other sign of ageing could be treated, a process called somatic mutation would still slowly wear down the body's ability to function. Somatic mutations are tiny mistakes that can arise in DNA every time a cell divides. The findings mean humans cannot live forever, even with a perfect anti-ageing medication, according to the researchers.
The average life expectancy for people living in the UK today stands at 83 for women and 79 for men. The researchers say some people could theoretically live far longer than 190 years, up to a maximum of 627 years old.
How ageing works at the cellular level
As people get older, their bodies pick up forms of wear and tear collectively known as ageing. At the biological level, these processes range from the shortening of protective caps on DNA strands called telomeres to cells losing the ability to clear out waste.
The researchers did not initially set out to calculate the ultimate limits of the human lifespan. Instead, they were trying to find a way of measuring how these processes contribute to ageing, and found that the buildup of somatic mutations would bring life to an end even if every other hallmark of ageing were treatable.
Cells are generally good at catching and repairing these DNA errors, but not perfectly. Most of the mutations are harmless, but they can sometimes give rise to cancer-causing changes. Even if medicine could keep cancer at bay, the researchers say the mutations themselves would eventually become fatal.
A hard limit on lifespan
Once somatic mutations build up to a certain level, they start to impair how cells function, wearing down tissues and eventually leading to organ failure. This puts a theoretical hard limit on how long a person could live.
Lead author Dr Dmitrii Kriukov said that realization raised the question of what the lifespan would be of a human who had overcome every ageing mechanism except somatic mutations. Dr Kriukov said the team built a model of human ageing driven solely by somatic mutations, estimating how the process alone affects lifespan by slowly depleting cells across tissues.
If medicine could treat everything besides somatic mutations, the model estimates average lifespans ranging between 146 and 194 years old, depending on which version of the model is used. Dr Kriukov said this is not a verdict of inevitability, but added that somatic mutations, while surprisingly weak as a standalone driver of ageing, may become critical when combined with other mechanisms.
Where treatments could work best
The researchers do not expect humans to start living this long any time soon, but their data points to where treatments could be most effective. They found that cells in the skin and liver continuously replace old cells with new ones and can keep this replenishment going for a very long time.
Cells in the heart and brain, by contrast, are largely irreplaceable, so they continue to accumulate mutations over the years.
Other efforts to extend human life
Earlier this year, the US-based startup Life Biosciences secured the first FDA approval for a human clinical trial investigating partial human de-ageing. During the trial, scientists will turn back the biological clock on damaged cells in a person's eye, aiming to rejuvenate the tissue and restore function.
Entrepreneur Bryan Johnson has said he believes his generation may be the first that will not die, and reportedly spends $2 million a year on an anti-ageing routine. The researchers' findings suggest that the pursuit of immortality through medical means could ultimately be a dead end.
