Most of the cells in your body have a natural lifespan, called the ‘Hayflick limit’. This is because chromosomes have biological bookends, called telomeres, that get shorter each time the cell divides. When the telomere shrinks past a certain point, the cell won’t divide any more and eventually dies. Statistical projections, based on the typical rates that our different cells divide, suggest an upper limit to our lifespan of around 120. This corresponds pretty well with what we observe: the longest lived person was Jeanne Calment, who died aged 122, and only a handful of others have made it past 110.
Cell lifespan isn’t fixed, though. When organs are transplanted into a younger body, the cells in the older organ live as long as the body into which they are transplanted. This may be because their telomeres grow longer again. Skin cells, sperm and some white blood cells can do this using the enzyme telomerase, and manipulating telomerase levels for other cells in lab animals does sometimes extend their lifespan. But it also seems to increase their cancer rates. In fact, there is evidence that cell ageing mechanisms evolved to protect multicellular organisms from cancer, so mortality might be inescapable.
What cells in the human body live the longest?
Although the our bodies are continuously replenishing their cells, some stick around for longer than others.
On average, the cells in your body are replaced every 7 to 10 years. But those numbers hide a huge variability in lifespan across the different organs of the body. Neutrophil cells (a type of white blood cell) might only last two days, while the cells in the middle of your eye lenses will last your entire life. And it’s even possible that your brain cells might have longer maximum lifespans than you do. In 2013, researchers transplanted neurons from old mice into the brains of longer-lived rats and found that the cells were still healthy after living for two whole mouse lifespans!
Brain cells: 200+ years?
Eye lens cells: Lifetime
Egg cells: 50 years
Heart muscle cells: 40 years
Intestinal cells (excluding lining): 15.9 years
Skeletal muscle cells: 15.1 years
Fat cells: 8 years
Hematopoietic stem cells: 5 years
Liver cells: 10-16 months
Pancreas cells: 1 year