Analysis of the world's oldest woman's blood suggests that lifespan of humans might ultimately be limited by the capacity for stem cells to keep replenishing tissues day in day out, scientists say.
Researchers led by Henne Holstege of the VU University Medical Centre in Amsterdam, the Netherlands, examined the blood and other tissues of Hendrikje van Andel-Schipper to see how they were affected by age.
Andel-Schipper, who was born in 1890, was at one point the oldest woman in the world.
The analysis suggests our lifespan might ultimately be limited by the capacity for stem cells to keep replenishing tissues continuously, the 'New Scientist' reported.
Once the stem cells reach a state of exhaustion that imposes a limit on their own lifespan, they themselves gradually die out and steadily diminish the body's capacity to keep regenerating vital tissues and cells, such as blood.
The other evidence for the stem cell fatigue came from observations that van Andel-Schipper's white blood cells had drastically worn-down telomeres.
Telomeres are the protective tips on chromosomes that burn down like wicks each time a cell divides.
On average, the telomeres on the white blood cells were 17 times shorter than those on brain cells, which hardly replicate at all throughout life, the report said.
"It's estimated that we're born with around 20,000 blood stem cells, and at any one time, around 1000 are simultaneously active to replenish blood," said Holstege.
She said during life, the number of active stem cells shrinks and their telomeres shorten to the point at which they die - a point called stem-cell exhaustion.