When talking about living healthy, keeping cells and DNA in good shape it is not often discussed what that actually means. It means for example that we need to keep, yes that’s right, 37.2 trillion cells healthy. That is 37,200 billion cells that need to exist in harmony, receive nutrients and so on. It also puts perspective on topics like mutations, it only seems logical that with such massive amount of cells something goes wrong occasionally.
The number of 37.2 trillion cells comes from a study done in 2013. The authors estimated the amount of cells in organs and that added it up to get to the totals. Cell amounts in for example these organs and blood are:
- Liver – 360B cells
- Skin – 2T cells
- Kidney – 10B cells
- Heart – 6B cells
- Nervous System – 3.1T cells
- Blood – 28T cells
With such huge amount of cells the amount of cells that die and are renewed are as consequence also impressive. Studies have shown that cells in the body renew at different rates depending on the organs. For example cells in the stomach renew in 2-9 days, skin epidermal cells every 10-30 days, red blood cells renew about every 4 months and fat cells are the slowest to renew with once every 8 years. It is also good to mention that some cells never renew like the lens cells and nervous system cells. You can find a table listing the renewal rates for various tissues and organs here.
So knowing we have 26T red blood cells with a renewal rate of every 4 months it means the body creates 216B new red blood cells every day. That is an amazing 2.5 million red blood cells per second.
Going through literature the estimates for overall cells renewal rates vary around 50-70B / day. The above numbers about cell amounts and renewal rates would indicate this is too low. For example in wikipedia the 50-70B number is based on literature, that is cited in that article, in which the researchers assume the total amount of cells in the human body at 13B cells. When using the newer study of 37.2T cells in the body this would indicate a cell renewal rate of 140-200B cells per day.
These numbers and renewal rates give food for thought:
- If one in a thousand cells mutates during renewal, for any reason, it means our body generates some 100M mutated cells / day.
- The fibroblast cells in skin renew every 60 days, the epidermis every 30 days but still we have wrinkles and aging skin indicating the skin cell age is not the cause.
- …and many more topics come to mind if you think about these statistics
Knowing the total cell number of the human body as well as of individual organs seems important from a cultural, biological, medical and comparative modelling point of view.
Extra note: For those really in big numbers it may be interesting to know that according to an estimate made by engineers at Washington University each cells consists approximately out of 100T atoms. That makes 100T x 32.7T = 3.2 x 10^27 atoms in the human body!