Is there a theoretical upper limit to human life?

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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

If our body cells are replaced, why do we age?

Most cells in our bodies divide and are replaced when they die, but we can’t rely on this process forever, especially when our DNA is setting the timer.

The cells in our bodies live for anything from a few hours, in the case of certain types of white blood cells, to a few weeks, for skin cells, to many decades, in the case of most brain cells. But while most cells are regenerated, the processes involved become progressively unreliable over time. In particular, the DNA carrying the instructions for cell processes becomes damaged, eventually preventing any more cell division. The result is the increasing level of decrepitude we call ageing.

nate henry

nate henry

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nate henry
nate henry

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