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It have heard several times that, every seven to ten years, all the cells that our body are made of have all been replaced. Example in this NY Times Article

This heartening truth, which arises from the fact that most of the body's tissues are under constant renewal, has been underlined by a novel method of estimating the age of human cells. Its inventor, Jonas Frisen, believes the average age of all the cells in an adult's body may turn out to be as young as 7 to 10 years.

Is this claim accurate?

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Yeah, but even that would be akin to saying all people on the earth will be dead in 100 years. It's only a statistical inference. Of course few people live longer than 100 years, but it's not in any way an absolute statement. –  Asaf Feb 3 '12 at 13:51
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I recall hearing that all atoms in the body are replaced every X period. Cells certainly arent' all ever replaced. –  Ben Brocka Feb 3 '12 at 22:16
    
@BenBrocka that may have come from Carl Sagan IIRC –  Sklivvz Feb 3 '12 at 23:44

2 Answers 2

Different types of cells have different lifespans, e.g.:



I want to throw in a philosophical side note and quote computer scientist Steve Grand:

"Think of an experience from your childhood. Something you remember clearly, something you can see, feel, maybe even smell, as if you were really there. After all, you really were there at the time, weren’t you? How else would you remember it?

But here is the bombshell: you weren’t there.

Not a single atom that is in your body today was there when that event took place … Matter flows from place to place and momentarily comes together to be you.

Whatever you are, therefore, you are not the stuff of which you are made.

If that doesn’t make the hair stand up on the back of your neck, read it again until it does, because it is important."


[Richard Dawkins uses this quote in his TED Talk (around 10:20)]


More:

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I'm confused; are you throwing in that quote to show that a quote can sound really profound while being completely false, or are you implying that while some cells are never replaced, every single atom actually is? –  romkyns Feb 6 '12 at 17:57
    
@romkyns - The quote is meant to be philosophical food for thought. Does every atom in our body get replaced at one point? I don't know. But since cells have a "metabolism" there is a constant flux of new molecules (and therefore atoms). –  Oliver_C Feb 7 '12 at 16:41
    
@romkyns: Why do you think the claim about atoms being replaced is completely false? –  endolith Nov 17 '13 at 18:54
    
Note that @endolith has now asked this as a separate question: skeptics.stackexchange.com/questions/18427/… –  Oddthinking Nov 18 '13 at 1:52

No, it isn't true that all the cells in our body are replaced every 3/7/10 years.

Some cells are never replaced.

In this article about the eye:

R.G.A. Faragher, B. Mulholland, S.J. Tuft, S. Sandeman, P.T. Khaw, Brief review on aspects of aging and the eye: Aging and the cornea Br J Ophthalmol 1997;81:814-817 doi:10.1136/bjo.81.10.814

they explain:

Non-dividing cells are those from static cell populations (exemplified by cerebral neurons) which never divide during adult life.

To support this, they cite an earlier article (which I haven't read):

Leblond CP(1964) Classification of cell populations on the basis of their proliferative behaviour. Natl Cancer Inst Monogr 14:119–149.

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Does it logically follow that non-dividing cells never die or are never replaced? Could they be replaced by stem cells? Just curious. –  Brian M. Hunt Feb 3 '12 at 14:57
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@BrianM.Hunt they are never replaced. If they die, they're gone. That's why some diseases and injuries (like certain eye problems) can never be healed by regenerating tissue. –  jwenting Feb 3 '12 at 15:05
    
Also true for most neurons –  nico Feb 3 '12 at 15:48
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@Alenanno: Perhaps not, according to somewhat recent research. –  Oddthinking Feb 3 '12 at 15:58
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@Alenanno: just do a Pubmed search for neurogenesis :) new neurons can definitely be generated even in adults, and not only in response to injury. –  nico Feb 3 '12 at 20:08

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