| 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.
Update: An article about Dr. Frisén’s continuing research appeared in New Scientist on June 10, 2013: http://www.newscientist.com/article/dn23665-nuclear-bomb-tests-reveal-brain-regeneration-in-humans.html
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.
I read that in “A Short History of Nearly Everything” by Bill Bryson.
I heard the 7 years theory in the movie “waking life”
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.
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!
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
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.
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.
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.
I just heard the myth on the Mentalist tonight.
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.
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.
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/#shermer
Hope it helps!
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.
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
I heard it in a philosophy class.
I heard the 10 years theory from my science teacher at school:/
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.
Read the ten year theory for the first time in old college notes of a family friend. This was somewhere between 1919 and 1921.
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.
I just heard the 7 years theory in the movie Griff.The.Invisible.2010
and here are the infos for the movie on wiki : http://en.wikipedia.org/wiki/Griff_the_Invisible
also this post is from october 2010
my question would be : any resent news ?
I read about the 7 year theory in a book by spiritual guru Anthony DeMello.
I read that US antrophologist John. E. Pfeiffer (* 1914) stated this “7-year rule” this in his book Human Brain (1955).
I think I am almost quoting Richard Dawkins correctly from “The God Delusion” . . .Think of a strong memory from your childhood and realize that now not one of the cells (maybe he said atoms) still exists in your body today.
Most similar facts you hear with ‘7’ in them are made up. This could be because of the rumoured tendency of humans to favour the number 7. Or it could be that this is also one of the made-up facts!
What about the ATOMS? bill Bryson said every atom in your body will be different. On each (well, most) of your cells, there’s a phospholipid bilayer. This layer is not static, rather, it moves around. The cell will undergo endocytosis, or exocystosis, gaining, or losing atoms, or organelles. So, I’m sure a cell that hasn’t divided for 30 years could have different atoms and thus in a way has replaced itself.
thoughts?
Hello,
The overall turnover rate of cells, in humans, in a year, is roughly equal to the total amount of cells at any given time (~3E14). In plain english: the ‘body’ is turned over once every year. Obviously so, perturbation of cellular homeostasis would result in significant recombosition of the body. Importantly, this quantification is cell-unspecific, as mentioned above. Certain cells have turnover rates that are very high (GI tract; turnover of 4-5 days) and others very slow, if at all (certain terminally differentiated neuronal cells). Notably, ~2.5E6 erythroblasts (red blood cell precursors) are produced every second (totalling a large constitutent of the total body turnover) and ~95% of these are sacrificed by apoptosis in the bone marrow before maturing and leaving the haematogenic system.
In short, the notion that the body turns over every 7-10 years is unequivocally a misconception by the general population. Alternatively, the quantification could have orignally encompassed only a subset of cells. Arguably, the 10 year turnover originite from the turnover rates of bone: ~10% of bone turn over every year totalling a total turnover every decade.
Several situations exist where normal hyperplasia singificantly increase turnover rate exist aswell; Following weaning of offspring the mammaries undergo involution resulting in apoptosis in 90% of the epithelial cells. In plain english: cells in breasts are increased in number by 1000% during pregnancy and turned over significantly more frequently. (Obviously, the breasts do not grow 1000% in volume during this time.) This turnover is of cells that normal breast do not possess. Another exmaple is hyperproliferation of tissue following damage: notably, the liver is the only organ that can compeltely regenerate (~5-10% of liver needs to be intact in order to grow back). Another example is following consumption of alcoholic beverages that denude cells in the throat greatly increasing turnover. Many more examples are readily available in the literature.
For the interested (or academic): turnover rates are easily demonstrable by using 3H-thymine or 5-bromouracil pulse-chase assays in the Liberkühn crypts, for example.
In conclusion, the entire notion is monumentally ambiguous and uninteresting. Turnover rates can only be described in a cell- and situation-specific context.
Sincerely yours,
Dr. K
Cancer Biologist
P.S. I stumpled upon this blog entry when I googled an Nature article containing the word ‘turnover’ (albeit in the context of a protein) in the title.
P.P.S. Do not trust physicians when it comes to science. They are clinicians not doctors and only called doctors as a courtesy phrase.
Certainly compounds lose and gain atoms all the time. And you’re probably right that most atoms in most cells, atoms in compounds get turned over frequently. Of course if that’s the level we’re looking at, then nothing on earth is ever stable. And why stop there? You could also say that the protons and electrons, or quarks for that matter, in everything are constantly turning over.
Dr. Frisén’s research, however, suggests that in at least some cells, the turnover of atoms in DNA molecules is very low. Otherwise, the radioactive isotopes from nuclear fallout would have been incorporated in cells formed during the peak fallout years.
I stumbled across this blog which asked the question about any evidence of cellular regeneration. While clearly some cells do regenerate, there are differing opinions on how and how often and if they all do!
Here is an interesting study on the issue worth reading:
http://stemcell.stanford.edu/research/
Warm regards
GUY MURCHIE’s THE SEVEN MYSTERIES OF LIFE, PAGE 321-322
Doctor Alex Comfort who studied ageing and wrote a book on sex to earn some money mentioned the seven year theory pointing out that a trigger in later years stops perfect replacement. I remember David Attenborough being told by scientists the evolution was an unproven theory, so if we have evolved why would we have a perfect cell replacement system that for an unknown reason decides to fail. The Bible tells us that we are mortal and will live for as long as God says. 900 years in the early days decreased at present to 70 years and that if we care for each other and love our God we could earn eternal life. Eternal life being pointless if we insist on trying to kill each other so we can have more money to give us the power to oppress.
“I remember David Attenborough being told by scientists the evolution was an unproven theory”
Nonsense, even if that’s what David Attenborough was told “by scientists” (which scientists? what kind of scientists?). Theories aren’t proven, it’s a matter of what best fits evidence. Actual evolutionary biologists would tell you that evolution has more evidence than many other theories–it’s very solid–and the fossil record hasn’t disproved it, for example by the order of fossil strata being incorrect.
Our ability to replace cells is not perfect. They are all subject to damage. Ageing is under ongoing research, but genetic damage, and specifically telomere damage have been implicated as contributing to declining vigor with age.
Well, the idea that evolution is an unproven theory is technically true because no scientific theory is ever “proven.” As hexalm says, every theory is continually judged on how it fits and predicts the evidence. But the “theory” of evolution fits an enormous amount of the evidence we see in the world and no evidence has been found that conclusively disproves it. So, yes, it is an “unproven theory,” but it has far more explanatory power than any other theory about how the biological world functions and changes.