| The Question: I’ve read various internet articles that say that human beings replace “every cell in your body” every X years (usually 7, but sometimes 10). What’s the real deal? Submitted by: Rick, NY |
The Short Answer: Recent research has confirmed that different tissues in the body replace cells at different rates, and some tissues never replace cells. So the statement that we replace every cell in the body every seven years or every ten years is wrong. Using a revolutionary new technique (described below), researchers have shown that:
- Neurons in the cerebral cortex are never replaced. There are no neurons added to your cerebral cortex after birth. Any cerebral cortex neurons that die are not replaced.
- Fat cells are replaced at the rate of about 10% per year in adults. So you could say that on average, human beings replace all their fat cells about every ten years.
- Cardiomyocyte heart cells are replaced at a reducing rate as we age. At age 25, about 1% of cells are replaced every year. Replacement slows gradually to about 0.5% at age 70. Even in people who have lived a very long life, less than half of the cardiomyocyte cells have been replaced. Those that aren’t replaced have been there since birth.
Scientists are now studying other tissues to determine the turnover rate.
More Information: What’s a little confusing about the data given above is that obviously, our brains grow bigger after birth, and so do our hearts. So where is all the extra bulk coming from? In the brain, no cerebral cortex neurons are added, but research hasn’t been completed on other parts of the brain, and even if it were to turn out that no other neurons are added, lots of other kinds of cells are added. Glial cells, for example, may actually make up 90% of the cells in the brain. It used to be thought that glial cells were simply the scaffolding of the brain, with no real role in the processing of the brain. In recent years, however, it has become clear that glial cells play key roles in processing.
Cardiomyocytes are the true muscle cells of the heart, but the heart is also made up of connective tissue and other cell types that may turn out to have different growth and replacement rates. And while cardiomyocytes replace very slowly, and some are never replaced, the individual cells do grow in size.
The Interesting Science: The technique used to investigate the replacement of cells in humans ingeniously utilizes the unfortunate fact that during the Cold War the nuclear states conducted above ground nuclear tests that spread radioactive Carbon-14 all over the globe. Carbon-14 combines with oxygen in the atmosphere to form CO2. This results in a mixture in the atmosphere of CO2 formed with normal, non-radioactive Carbon-12 or Carbon-13, and CO2 formed with Carbon-14. This CO2 is then used by plants such as wheat and eaten by animals such as cattle. When we eat crops or livestock, the mixture of Carbon-12, Carbon-13 and Carbon-14 becomes part of our cells, and most importantly, part of the DNA formed when a new cell is born. Since the DNA is not replaced over the life of a cell, the Carbon-14 in a cell’s DNA when the cell is born is pretty much the Carbon-14 it will always have. Since we know how much Carbon-14 was in the atmosphere before nuclear testing, we know how much was in the air during the testing years, and we know how it was eliminated from the atmosphere after the Nuclear Test Ban Treaty outlawed above ground testing in 1963, it’s possible to estimate the turnover of cells.
For example, if a person born just before nuclear testing shows no Carbon-14 from the fallout years in his cerebral cortex neurons, that suggests that no cerebral cortex neuron cells were added after birth. If any new cells had been formed, they would have incorporated Carbon-14 into their DNA. If, on the other hand, a person born right at the peak of the fallout years shows little or no fallout Carbon-14 in his cerebral cortex cells, that would suggest that all the cerebral cortex neuron cells had been replaced. They would have incorporated non-radioactive carbon into their new DNA relatively recently, after most of the Carbon-14 had been washed out of the atmosphere. Otherwise most of them would have some Carbon-14 still in the DNA from when the person was born during the height of the Cold War.
This is a very much simplified version of what a team lead by Dr. Jonas Frisén at the Department of Cell and Molecular Biology at Karolinska Institute in Sweden has been doing. It is their studies that produced the estimates for turnover of cerebral cortex neurons, fat cells, and cardiomyocytes given above.
By the way, Dr. Frisén is very interested in tracking down the origin of the “We replace every cell every 7 or years” myth. If any readers have information on where they heard or read this idea, leave a comment on this page by clicking below and I’ll forward your information to Dr. Frisén.
Sources:
Evidence for Cardiomyocyte Renewal in Humans. Olaf Bergmann, Ratan D. Bhardwaj, Samuel Bernard, Sofia Zdunek, Fanie Barnabé-Heider, Stuart Walsh, Joel Zupicich, Kanar Alkass, Bruce A. Buchholz, Henrik Druid, Stefan Jovinge, and Jonas Frisén. (3 April 2009) Science 324 (5923), 98.
Dynamics of fat cell turnover in humans. Spalding KL, Arner E, Westermark PO, Bernard S, Buchholz BA, Bergmann O, Blomqvist L, Hoffstedt J, Näslund E, Britton T, Concha H, Hassan M, Rydén M, Frisén J, Arner P. Nature. 2008 Jun 5;453(7196):783-7.
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27 Responses
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Kevin Says:
I read that in “A Short History of Nearly Everything” by Bill Bryson.
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winston Says:
I heard the 7 years theory in the movie “waking life”
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rand om Says:
i’m not religious, but i researched this and found references to releasing all debts every 7 years in Deuteronomy 15 (bible for those of you who don’t know)… My guess is the idea of our renewal of self might have a foundation in this.
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The cells of our body regenerate every 7 years. - Interfaith forums Says:
[...] cells of our body regenerate every 7 years. Ask a Naturalist.com Do We Replace Our Cells Every 7 or 10 years? [...]
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Ask a Naturalist.com » Which Cells Are Never Replaced? Says:
[...] The Short Answer: So far, the only cell type that we can confidently say is never replaced is cerebral cortex neurons. Check out my posting a couple of months ago about the research of Dr. Jonas Frisén at the Department of Cell and Molecular Biology at Karolinska Institute in Sweden. Dr. Frisén has developed a very clever way to measure the replacement of cells in the human body. Like most careful science, this research takes time, of course. So far, Dr. Frisén and his team have only gotten definitive results on cerebral cortex neurons, fat cells, and cardiomyocytes (heart muscle cells). This research suggests that cerebral cortex neurons are never replaced. Fat cells are replaced fairly regularly, and cardiomyocytes are replaced at a decreasing rate with age. Click here for the full article: http://askanaturalist.com/do-we-replace-our-cells-every-7-or-10-years/. [...]
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Jake Says:
Greetings
First of all, very interesting. I recall learning that our eyes, skin, and many other parts are replaced several times during the span of our lives. Would anyone be able to confirm this and possibly provide a rough estimate as to how many years it takes for eyes, skin and other organs to regenerate?
Thanks very much in advance!
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Mandy Says:
http://www.scholarpedia.org/article/Adult_neurogenesis
NEW NEURONS IN THE ADULT HUMAN BRAIN THROUGH THE PROCESS OF ADULT NEUROGENESIS. New neurons grow in the brain well into adult in the olfactory area and in the dentate gyrus of the hippocampus. These newborn neurons integrate into existing circuitry – and researchers postulate they may play a role in keeping memory details from overlapping, and in adding a new time component to old memories.
Paradigm shift in Neuroscience – keep reading more by searching google scholar! neurogenesis and neurorehabilitation
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John Fee Says:
I heard over 40 years ago at Nottingham Bible Institute (now defunct) from Rev H Brash Bonsall MA, BD (now deceased) – the founder and then Principal of Birmingham Bible Institute – that ‘every cell in your body is replaced every seven years, except the enamel on your teeth’. Mr Bonsall would not himself have been the authority for this statement, but he would have believed it to be the received wisdom of other reputable authorities at that time.
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Quora Says:
Does an adult human keep cells or molecules from his/her newborn days?…
The notion that every cell on our body regenerates every x years unfortunately turns out to be wrong. That makes me sad, because the thought of scientists researching how dying neurons transferred data to new ones was mouth-watering. I know for sure th…
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mfratlanta Says:
George Bernard Shaw, in the Preface to the 1905 edition of his novel The Irrational Knot:
“At present, of course, I am not the author of The Irrational Knot. Physiologists inform us that the substance of our bodies (and consequently of our souls) is shed and renewed at such a rate that no part of us lasts longer than eight years: I am therefore not now in any atom of me the person who wrote The Irrational Knot in 1880. The last of that author perished in 1888; and two of his successors have since joined the majority. Fourth of his line, I cannot be expected to take any very lively interest in the novels of my literary great-grandfather.”
The ‘myth’ appears to be over 100 years old. -
bglassman Says:
If one wants to chart myths, you might want to see what happens to the statement in “The Secret Life of Plants” that all human cells are completely replaced every 6 *months*!
http://uncsphne.ws/secretlife
How good is the rest of the science-writing in a book that makes that kind of error? Of course, now I really want to read it. -
Communication with a Transsexual Cult – Final Transmission | Jade Hunter Says:
[...] being, we are actually able to use Google search and find out simple information such as that full cell replacement over seven to ten years is a myth. Have you taken a human physiology class? A basuc Health Class in high [...]
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Self Portrait Loathing : David Spratte Says:
[...] looking to take shots of people out in the world. Either theirs or mine. It doesn’t matter. The average human body will regenerate most of its cells every 7–10 years. You’re a fundamentally different person every decade—I want to remember who these people [...]
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Kim Says:
I just heard the myth on the Mentalist tonight.
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Anon Says:
This myth was repeated on the CBS TV show The Mentalist on 4/17/2011 in episode S03E19 at the 1 minute 8 second mark.
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Nothing About Potatoes | Things I found on the internet. Cannot guarantee 100% potato-free. Says:
[...] Puzzle On the subject of the body’s constituent molecules being replaced every seven years, some interesting things to consider are tattoos, memories, teeth, and ova. A proper scientific answer with real experiments and references and everything can be found here. [...]
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Anonymous Says:
My philosophy teacher told my class (while discussing personal identity) that all of our cells are replaced after seven years; however, some scientists contend that there are a few cells in the brain that are not replaced.
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Akamaiehu Says:
The 2011 “Through the Wormhole 2, Is there life after death?” TV series that debuted 6.08.11 repeated the 10 year total body replacement (cellular renewal) claim–ironically enough, on the so called “Science Channel.”
As with all claims brandishing the “Science” designation, caveat emptor. And for those who need a basic understanding of the critical difference between valid science and junk science, check our the “Baloney Detection Kit” on the Skeptic dot come website, here:
http://www.skeptic.com/eskeptic/09-07-01/#shermerHope it helps!
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wamba7 Says:
I recall being told by a physician that there are changes in the immune system every 7 years or so, which can trigger a change in allergic reactions. This could explain why I used to be able to roll in poison ivy patches wearing shorts and a T shirt without developing a rash. Nevertheless, I avoided it as I got older and so I didn’t exerience reactions.
At some point in my 30s, I became aware that for me, the rolling around thing was no longer such a great idea – in short, I was no longer immune. At about the same time, though, I became “relatively” immune to hornet stings (I literally walked into a nest and was stung 15-20 times on my leg, causing only a little pain, numbness and swelling – my legs still worked well enough to get me away before I was stung more).
But physicians are sometimes susceptible to fad science too, so I may have gotten false information. Maybe certain immune cells were just wiped out with age and not replaced.
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Mark Says:
I dont know where the seven year replacement myth comes from, but I think there is some confusion about cells vs. atoms. There was a study done at Oak Ridge Lab. by Paul C. Aebersold in 1953 that found that 98 percent of all the atoms in a person’s body change out every year, and that within five years all the atoms had changed. Even cells that are not replaced, in the brain for example, must carry out some sort of activities and energy exchanges or they would die. Part of those processes results in the complete replacement of every atom in the cell. I found your article by accident while looking for a copy of the 1953 study. I found a copy, but do not want to pay the $32 for the right to read it. I did find a 1954 article from “Time” about the report. I posted the link below. And an unsourced quote from another article about the 1953 study I found on a blog.
Unsourced quote from http://www.reddit.com/r/askscience/comments/g63l6/are_98_of_the_atoms_in_the_human_body_replaced/
Studies at the Oak Ridge Atomic Research Center have revealed that about 98 percent of all the atoms in a human body are replaced every year. You get a new suit of skin every month and a new liver every six weeks. The lining of your stomach lasts only five days before it’s replaced. Even your bones are not the solid, stable, concrete-like things you might have thought them to be: They are undergoing constant change. The bones you have today are different from the bones you had a year ago. Experts in this area of research have concluded that there is a complete, 100 percent turnover of atoms in the body at least every five years. In other words, not one single atom present in your body today was there five years ago.
URL for the Time article
http://www.time.com/time/magazine/article/0,9171,936455,00.html
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jack Says:
I heard it in a philosophy class.
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P987 44 hari bersama cucu « Keluarga Sharif Yamah Says:
[...] kepada yang mengkaji. Ada yang mengatakan hayatnya 7 – 10 tahun (The ‘myth’ appears to be over 100 years old.), tetapi ada yang tidak bersetuju, seperti di atas. Cara pengukuran yang menarik perhatian saya, [...]
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Katy Says:
I heard the 10 years theory from my science teacher at school:/
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Elizabeth Says:
I heard this nearly 30 years ago, I think, in an introductory philosophy class, in a discussion on the pre-Socratic view of essences and identity.
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heather Says:
Read the ten year theory for the first time in old college notes of a family friend. This was somewhere between 1919 and 1921.
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The Perfect Diet - Guaranteed! | Genuine Thriving Says:
[...] pretty important issue to people and rightfully so. Did you know that most cells in the human body renew themselves? Meaning, the cells that make up the skin on your arm will not be the same cells that make up the [...]
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viki Says:
so eventually,what is it,7 or 10 yrs? i read about this over 30yrs. ago,but now i,me alittle mudled as to what to believe.