The longevity effects of drugs like Rapamycin are more like a “biological lottery” with their benefits varying widely between individuals, a new study finds.
A key aim of such drugs is not only to work at the individual level, but also to ensure that humans live longer at a population scale with less variation among people in their age at death.
To study this variation, researchers use what’s called a “survival curve” – a graph that shows how many individuals in a population are still alive at different ages.
In societies facing high early mortality, this curve slopes down gradually as many die young, others at middle age, and some live longer.
Previous studies anticipated that lifespan-extending treatments like Rapamycin would “square the survival curve” of the population as mortality is compressed more towards a narrower age window near the end of life.
However, the new research review found that this is not the case.
Researchers assessed lifespan extension interventions cited in 167 studies, conducted across eight non-human species, including fish, mice, rats and rhesus monkeys.
Scientists found that across datasets, the longevity benefits among individual animals were variable.
“This suggests that lifespan-extending treatments do not reduce variance and ‘square the survival curve’,” researchers wrote in the study published in the journal Biology Letters.
"These approaches can make animals live longer, but the benefits aren't shared equally. Without more information, the outcome looks like a biological lottery,” said biologist and study author Tahlia Fulton from The University of Sydney.
The latest finding suggests that approaches like dietary restriction or drugs such as Rapamycin or Metformin may be likely beneficial for longevity, but how much benefit they offer is unclear.
It also reframes how anti-ageing breakthroughs are to be interpreted, hinting that future therapies may not produce uniform outcomes.
“Some individuals will be much longer lived, some will be a little longer lived, and some might not live any longer than they would have anyway,” Dr Fulton told New Science.
“We're working to understand why, so future longevity science helps everyone,” she said.
Researchers are yet to fully understand the relationship between lifespan extension and healthspan, which is the number of years spent in good health.
While anti-ageing therapies may lead to some people living much longer, this may be accompanied by extended periods of frailty, the study suggests.
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