Cells, like people, can show signs of aging. But researchers haven’t been sure whether our aging goes hand-in-hand with that of our cells, and the uncertainty has hampered anti-aging research.

Now, biologists are reporting the first evidence that old cells indeed help make old bodies.

The uncertainty over the question has been a problem for researchers who seek to study possible anti-aging therapies the easiest way—testing them on cells. If cellular aging has nothing to do with the aging of our bodies, that effort might be a waste of time.

The idea that cellular aging and the aging of a whole body are linked may seem obvious, but the lack of evidence to date made it “highly controversial,” said John Sedivy of Brown University in Providence, R.I., senior scientist on the project.

“Skeptics say ‘Show us the evidence.’ The first solid evidence is in this study. These initial findings won’t settle the debate, but they make a strong case.”

The researchers said their study showed that as baboons age, the number of aging cells in their skin significantly increases. The “aging” of cells is technically called replicative senescence, a term that means the cells are losing their ability to divide.

The study, published in an advance online edition of the research journal Science, is the first to quantify the number of such cells in any species, Sedivy said. This is despite the fact that scientists have known of replicative senescence for 40 years.

Human cells divide between about 60 and 90 times before senescence sets in. Scientists believe the process functions in some ways as a safeguard against disease. But senescent cells are also associated with skin wrinkles, delayed wound healing, weakened immune system response and age-related diseases such as cancer.

“There is good evidence that senescent cells are not benign,” Sedivy said. “But until now, no one has been able to confirm that they exist in appreciable numbers in old animals.”

The scientists studied baboons from a research preserve, ranging in age from 5 to 30. In human years, that age range is roughly 15 to 90.

Replicative senescence is marked by a shortening of strings of DNA in cells called telomeres: as normal body cells age, their telomeres tend to get shorter and shorter. The scientists found that in baboons, the number of senescent cells increased exponentially with age, at least in the cell samples studied, which came from regions in the body known as connective tissue.

“This research confirms that telomeres are important in aging,” Sedivy added. “But we’ve only scratched the surface… I am eager to see if the same patterns play out in other tissue.”

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