The cellular mechanisms behind human health begin to wind down once we reach our 50s — but some of those cells are more durable than others.

That’s the picture painted by two new studies published last week. Between them, they suggest new ways to extend healthy human lifespans.

The first study, published in Aging Cell, is the product of two decades of research into tissue-coding and noncoding RNA.

The study’s leaders, Claes Wahlestedt, M.D., Ph.D., professor of psychiatry and behavioral sciences and associate dean for therapeutic innovation at the University of Miami Miller School of Medicine, and Jamie Timmons, Ph.D., of King’s College London and Stirling University Science Park (U.K.) started their collaboration at the Karolinska Institute in Stockholm, Sweden.

The researchers found that human muscle and brain tissue rely on a protein complex called mTOR as well as mitochondrial reactive oxygen species production to create healthy new cells. Sometime after age 50, those mechanisms start to break down at increasing speed, increasing the rate of disease among older people.

“For over a decade, it has been clear that key biochemical events regulate the longevity of small short-lived animals such as worms, flies, and mice, but these mechanisms had not been observed to be active in humans,” Dr. Wahlestedt said in a press release.

Researchers identified groups of long-lived brain, liver and pancreas cells and proteins.

“Our study revealed that the complexity of regulation of aging programs may be much greater in humans as compared to other species,” Dr. Wahlestedt said. “This is related to our more complex genome, which may have evolved to allow for longer and healthier lifespan. But perhaps humans were not really meant to last beyond their 50s.

Meanwhile, however, some human cells hold up a lot longer, according to an institute from the Salk Institute published in Cell Metabolism.

Challenging earlier assertions that neurons, or possibly heart cells, were the oldest cells in the body, the researchers identified groups of equally long-lived brain, liver and pancreas cells and proteins. The team identified this “age mosaicism” in mice, and suggested that nearly any tissue in the body can maintain its integrity for the long run.

Bottom line: Our biological clocks run on the metabolism of cells.

“Biologists have asked — how old are cells in an organism? There is this general idea that neurons are old, while other cells in the body are relatively young and regenerate throughout the organism’s lifetime,” said Rafael Arrojo e Drigo, first author and Salk staff scientist, in a press release. “We set out to see if it was possible that certain organs also have cells that were as long-lived as neurons in the brain.”

Bottom line: Our biological clocks run on the metabolism of cells. Continuing to study the reasons why some cells outlast others could provide clues that can slow the gears and extend our healthy years.

Watch this