You are a Clone of your Former Self! How Old are Your Cells?
I often get asked by patients how long it will take for bone marrow to regenerate once it’s removed to harvest stem cells. A researcher in Sweden has begun to answer these and other questions using a new technique that involves carbon 14 dating of the cell’s DNA. His results are surprising in that certain areas of your body are much younger than you would think.
The body is dynamic and constantly changing and this is accomplished by most of the body replacing itself. This is a hard thing for most people to accept and conceptualize. However, it’s why we have adult stem cells, which serve as the reserve cells that spring into action to replace worn out cells. In some areas, the worn out cells are replaced very rapidly and in others more slowly.
The researcher here from Karolinska Institute came up with a unique way of looking at the age of cells in different areas by borrowing a technique from archaeology. Carbon 14 is a molecule that’s present in all living things and it decays at predictable rates. You can therefore measure the age of a living thing by looking at the amount of decay, sort of like a biologic clock. Frisen and colleagues looked at the carbon 14 turnover in the DNA of cells, applying a macro dating technique to these tiny cells.
So how old are your cells in various parts of your body? All of this is taken from various papers by Frisen’s group listed in PubMed:
-The part of your brain that registers smell is as old as your birth age, indicating that there isn’t much cell turnover here.
-On the other end of that spectrum, the cells lining your intestine only last about 5 days!
-Deeper cells in the intestine (not the lining) last about 16 years. However, realize that this means your entire intestine after 32 years has already made two complete copies of itself!
-The muscle cells between your ribs replace themselves every 15 years. Assuming this applies to other muscle cells, this means your muscular system makes a new copy of itself about every 15 years! Your bones are only about 10 years old, so your entire musculoskeletal system is regenerating every 1-2 decades.
-Your liver copies itself every 1-2 years
-Your fat cells make a total copy of themselves every 10 years (with about 10% of the total being replaced every year)
-Your blood only lasts about 4 months, so you replace it about 3 times a year. Your bone marrow would be similar.
The upshot? Your body is dynamic and constantly changing. Many parts are making copies of themselves in days to months to years. Outside of most of the cells in your brain, the rest of you reading this blog has been cloned and replaced at least a few times in your adult life!