The blood of a woman who died aged 115 has lent support to a theory about why humans inevitably die.
Analysis of blood cells from Hendrikje van Andel-Schipper suggests that the eventual death of even generally healthy people may be because stem cells have a limited capacity to replenish tissue.
van Andel-Schipper was born in 1890 and died in 2005. She was at one stage listed by some sources as the oldest living person in the world (a disputed status) and is currently at number 25 in the all-time list of highest verified ages.
At the age of 82 (in the early 1970s) she gave written permission for her body to be donated to science after her death on condition any findings were made public. It proved a particularly useful bequest as not only did she make it to such a high age, but she remained in good physical and mental health throughout her life, in effect leaving her body as something of a control sample for geriatric health studies.
She died of a gastric tumor and her only other serious condition was a breast tumor; both conditions were highly localised, leaving the rest of her body affected only by the ageing process. She’s also the first person of such an extreme age whose brain showed no signs of dementia conditions such as Alzheimer’s disease.
The VU University Medical Center in Amsterdam explored samples of van Andel-Schipper’s tissue from across her body. They found a distinctive pattern by looking at telomeres, a part of a chromosome that reduces every time a cell divides, a process New Scientist likens to a finite wick burning down.
The research showed that the telomores on her white blood cells were 17 times shorter than on her brain cells. They also found that around two-thirds of her remaining white blood cells came from only two stem cells, suggesting the rest had largely died out.
According to the researchers, that suggests that her death from “old age” was the result of blood stem cells simply being worn down and the telemores shortening until the cell dies. With a finite number of blood stem cells (around 20,000 at birth), that puts a limit on human life.
The researchers also used van Andel-Schipper’s body to explore an alternative theory: that death is inevitable because of somatic mutation (changes in DNA during your life that are neither inherited nor passed on.) They found that although she had around 450 somatic mutations in her white blood cells, they were all a result of mistakes during the replication of DNA as the stem cells divided.
None of them had any danger of leading to a disease or cancer, meaning that for her at least, it was possible to avoid fatal consequences from such mutations long enough to push her stem cells to their limits.