Expert: Dana Krempels, Ph.D. - 8/3/2008

Question
I was told the other day that in three months my body will have replaced every cell in my body,n This would mean that your body would have totally new cells through its entire body every three months, This is not logical to me, How long would it take for you body to do this? How, how often and how long do does it take to replace all the cells in bones, organs, brain cells etc....

Answer
Dear Lois,

Not all cells replace themselves.  The cells of the nervous system, for example, are notorious for being unable to replicate and repair in the case of damage.  What we have at maturity is pretty much all we're going to get.  Similarly, the cells inside our bones and cartilage don't replace themselves.  They are situated where they are, and though their components may turn over as blood supply and nutrients constantly rebuild and repair, the cells themselves pretty much stay the same.

Since all the cells in our body come from cells that are already there, I'm not sure how one can really say that all the cells are different after a certain amount of time.  When a parent cell divides into two new daughter cells, do both new cells count as "new" cells?  Or are they simply progeny of the original cell, complete with the aging that this implies?  (As cells multiply, their progeny cells do age in various ways, with each cell division.)

I've heard the same claim that you're citing here, and though it sounds spectacular, I think it needs to be said with a whole lot of caveats.  

Hope that helps, for what it's worth.  :)

Dana