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Eelpie

"every atom in you is replaced after 7 years"

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Apologies if I have put this in the wrong forum, couldnt see anywhere in biology where this was quite right...

 

I often hear various permutations of the statement that every atom in your body is different after a period of x years. Is there an authoritative source for this? Secondly, surely there has to be a positive probability that some of the atoms in your body are the same after x years even if it is in acompletely different place...and a very small chance. Thirdly I am sure I read that after a certain age the body does produce any new brain cells, so presumably this means that for the 7 year rule to be true it must be somehow rebuilding the same cell?

 

Thank you!

Edited by Eelpie

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No, the 7 year rule is not true. This can be shown by analysing the amount of carbon 14 that is incorporated in to DNA. Carbon 14 is a radioactive form of carbon that is present in the atmosphere such that any plants that absorb carbon dioxide will contain a ratio of carbon 12 to carbon 14 that matches that in the atmosphere. As animals then eat plants, they too will be made up of a ratio of carbon 12 to 14 that matches that in the plants they eat. Now, between 1955 and 1965 testing of atomic weapons caused a dramatic increase in carbon 14 levels in the atmosphere. In 1963 with the test treaty ban coming into force, the amount of carbon 14 in the atmosphere slowly reduced. Measuring the ratio of carbon 12 to carbon 14 in cerebral cortex neurons from people born before the cold war, he earliest was born in 1933, and died in 2000's, showed that the most of DNA in these neurons had carbon 14 levels that caresponded to the levels in the atmosphere before 1955, and that therefore DNA synthesis had occurred before 1955, ie during childhood. DNA synthesis during adulthood made up less than 1%. Therefore most of the carbon atoms that form your DNA in neurons as a child are the same atoms that make up your DNA throughout your entire life.

 

 

John

 

source...

 

 

Bhardwaj et al. (2006) Neocortical neurogenesis in humans is restricted to development. PNAS August 15, 2006 vol. 103 no. 33 12564-12568

http://www.pnas.org/content/103/33/12564.full

Edited by JohnG

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That paper is an interesting read, but remember that carbon-14 is continously being generated in the atmsophere by the action of cosmic radiation on nitrogen atoms. So not all of the carbon-14 observed in the sample would have come from the nuclear testing.

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No, the 7 year rule is not true. This can be shown by analysing the amount of carbon 14 that is incorporated in to DNA. Carbon 14 is a radioactive form of carbon that is present in the atmosphere such that any plants that absorb carbon dioxide will contain a ratio of carbon 12 to carbon 14 that matches that in the atmosphere. As animals then eat plants, they too will be made up of a ratio of carbon 12 to 14 that matches that in the plants they eat. Now, between 1955 and 1965 testing of atomic weapons caused a dramatic increase in carbon 14 levels in the atmosphere. In 1963 with the test treaty ban coming into force, the amount of carbon 14 in the atmosphere slowly reduced. Measuring the ratio of carbon 12 to carbon 14 in cerebral cortex neurons from people born before the cold war, he earliest was born in 1933, and died in 2000's, showed that the most of DNA in these neurons had carbon 14 levels that caresponded to the levels in the atmosphere before 1955, and that therefore DNA synthesis had occurred before 1955, ie during childhood. DNA synthesis during adulthood made up less than 1%. Therefore most of the carbon atoms that form your DNA in neurons as a child are the same atoms that make up your DNA throughout your entire life.

 

 

John

 

source...

 

 

Bhardwaj et al. (2006) Neocortical neurogenesis in humans is restricted to development. PNAS August 15, 2006 vol. 103 no. 33 12564-12568

http://www.pnas.org/...3/33/12564.full

 

 

Cheers just reading a slightly earlier paper by Spalding et al which makes broadly the same argument using carbon-14 analysis. It seems odd that the 7 year claim has become so ubiquitous when there is strong evidence for it not being true....

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Thirdly I am sure I read that after a certain age the body does produce any new brain cells, so presumably this means that for the 7 year rule to be true it must be somehow rebuilding the same cell?

 

 

 

Cheers just reading a slightly earlier paper by Spalding et al which makes broadly the same argument using carbon-14 analysis. It seems odd that the 7 year claim has become so ubiquitous when there is strong evidence for it not being true....

 

 

Yeah, i suppose the misconception could come from the fact that your body is constantly rebuilding the same cell, proteins are constantly being degraded and produced in all cells. Protein in the body has a half life of about 80 days, which means most of the protein in your body will be "new" after a few years.

 

John

 

 

 

Edited by JohnG

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That paper is an interesting read, but remember that carbon-14 is continously being generated in the atmsophere by the action of cosmic radiation on nitrogen atoms. So not all of the carbon-14 observed in the sample would have come from the nuclear testing.

 

I think the authors control for that, also "natural" C-14 is tiny relative to anthropomorphic C-14 of the subjects tested.

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No, the 7 year rule is not true. This can be shown by analysing the amount of carbon 14 that is incorporated in to DNA. Carbon 14 is a radioactive form of carbon that is present in the atmosphere such that any plants that absorb carbon dioxide will contain a ratio of carbon 12 to carbon 14 that matches that in the atmosphere. As animals then eat plants, they too will be made up of a ratio of carbon 12 to 14 that matches that in the plants they eat. Now, between 1955 and 1965 testing of atomic weapons caused a dramatic increase in carbon 14 levels in the atmosphere. In 1963 with the test treaty ban coming into force, the amount of carbon 14 in the atmosphere slowly reduced. Measuring the ratio of carbon 12 to carbon 14 in cerebral cortex neurons from people born before the cold war, he earliest was born in 1933, and died in 2000's, showed that the most of DNA in these neurons had carbon 14 levels that caresponded to the levels in the atmosphere before 1955, and that therefore DNA synthesis had occurred before 1955, ie during childhood. DNA synthesis during adulthood made up less than 1%. Therefore most of the carbon atoms that form your DNA in neurons as a child are the same atoms that make up your DNA throughout your entire life.

 

 

John

 

source...

 

 

Bhardwaj et al. (2006) Neocortical neurogenesis in humans is restricted to development. PNAS August 15, 2006 vol. 103 no. 33 12564-12568

http://www.pnas.org/content/103/33/12564.full

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There are some cell types that are completely recycled every few days and others that last a lifetime. Most of the components of our cells are also recycled over some period, but there are some molecules that never are (look up lipofuscin). Any estimate of turnover time would have to consist of a mean and standard deviation in order to get some idea of how this all works, but why would anyone pursue this for the whole body? These sorts of pseudo facts get imbedded in popular culture and this one has achieved the memehood of the downright silly supposed fact that we all only use only 10% of our brains. I think there is wonder enough in the realization that a large though imperfectly measured turnover of our cells and molecules doesn't appear to affect our personhood. SM

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Thanks everyone for the responses.

 

The C14 experiments I have found only look at DNA...does that mean the non-DNA parts of neurons are constantly being replaced? Could it be argued that although the majority of material in a brain cell is replaced after x numbers of years?

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Eelpie. Cells, including neurons, recycle molecular components on some time scale. SM

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Could it be argued that although the majority of material in a brain cell is replaced after x numbers of years?

 

The majority of material in your body is water(60%). An average male weighs approx. 72 kg. Therefore about 43.2kg is water. As 1 mole of water is about 18g, thats 24000 moles. 94 half lives later there will be 1 or less water molecule remaining. The biological half life of water in the body is between 4 and 18 days. If we take the max half life, 18, multiplied by 94 gives about 4 and a half years. Of course some of the hydrogen and oxygen present in that water will still be present due to its incorporation into proteins, lipids and DNA

 

 

so there you go, 4 and a half years and the majority of material in your body will be replaced.

 

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You must be right.... Seven years ago , I was a woman . Now Im a man. In the next seven years I hope to be a horse.

or at least hung like one .

 

IM sure there must be a genetic formula for that somewhere.

 

DH

 

Just joking all. In my studies we came to the conclusion that every cell in the body is replaced. The standard time frame is between five and seven years depending on genetically inherited metabolic rate.

 

One of my students said something to me one day that was most poignant.

 

quote "Isn't it just a copy of a copy of a copy ?"

 

True.

 

But as far as the integument is concerned. The copies replicate through the already confused DNA replication.

 

 

A great thread this is .

 

 

Hope you can appreciate a little irreverant humour on my previous post.

 

DH

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Come on guys ....doesn't every cell reproductive bloke want to be hung like a horse ?????

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You must be right.... Seven years ago , I was a woman . Now Im a man. In the next seven years I hope to be a horse. or at least hung like one.

 

Exaggeration as a way to prove or disprove statements relies heavily on "common sense". Now, "common sense" is a bad advisor in this field because we don't do atom tracking in our daily life. After all, common sense suggests that Sun is going around Earth.

 

So, we have to count if we are looking for a great price/quality ratio (as JohnG did here), or, if we only care about precision, measure (see the report of Ratan D. Bhardwaj in the Proceedings). However, we should define our terms before we start any calculations/measurements. Lets use analogy*. Here is a similar question:"Most of the car get replaced

(a) in 1 year,

(b) in 10 years,

© never?

 

(a) Is correct, because the car burns10 gallons of gas every week. 10 US gal/week x 6.073 Lb/US gal x 52 weeks/year = 3150 Lb/year**. So, Ford Focus (2641 Lb) consumes more gas then it weights in one year. For a dramatic result lets consider a container with water. Does it mostly change or mostly remains intact once we empty the container? Well, it depends whom you ask. Archeologist would say: "this ancient vase that we came upon at the bottom of the sea didn't lose any when we dumped water out of it". A traveler, parched with thirst and dying in a desert (with an empty canister) believes that a bottle of water is quite different from an empty bottle. Note that a bottle doesn't have to become "a horse a man or a woman"

 

(b) Is correct, because quite a few parts were replaced. Also, if you have to choose between two cars (same make, same model, same price, but different year) you will likely go for this year, than a 10 year old car. And, yet, it is the same car.

© Is also correct, because we can draw a continuous line through space-time that connects the new and the old car.

 

So, the question translates into "who am I and what are the necessery and sufficient components of me" everybody answers this question differently, hence the numbers vary". Measurement of flux (replacement of material over some period of time) gives the half-life: intrinsic value with a clear physical meaning, but this value upsets the subjects of the research. As subjects we want this value to be higher. Why higher (and not lower)?

 

I would speculate that humans realize that they change very fast. "Yesterday-Me" was drunk and happy, as a result "Current-Me" (which is the real me, because Current-Me perceives the world) has a hangover. And has to work so that "Tomorrow-Me" had some results to report to boss/client and "Year-Later-Me" got bonuses and longer vocation. Yesterday-Me is a mean guy because when he enjoys life Today-Me suffers. Future-Me is elusive (there is no guarantee of any kind, not even that "Year-Later-Me" will live). So, should I work for some vague guy in future if I can do something pleasant now? This idea is very old. You might recall that criminals in ancient Greece argued that the crime was committed by some other guy (Earlier-Me), so, why should Today-Me be punished? Clearly, these questions are counterproductive and dangerous to both the "philosopher" and his neighbors. As a result, people started to convince each other that you are the same person from birth to death. Arguments were simple: yes, your habits, manners, and behavior gradually change, but the body remains the same. Well, size changes, proportion change too .. but (ace of trump) you form a continuous line in space-time. The idea that body remains the same became a dogma. Nowadays we work for better tomorrow because we logically understand that we should and because we suppress feelings (the feelings suggest to enjoy life now) with the "same body" dogma. When one suddenly*** discovers that his body changes quite fast his carpe diem attitude surfaces. Some people give in and die out, others experience pain in the lower part of the back, but bite the bullet, go into denial, and win the evolutionary race.

 

PS. Peacocks lost the ability to fly, because females choose males with the biggest and brightest tail. This is a loosing strategy for the whole population. Losing ability to fly for nothing is a bad deal. Yet, this is a great strategy for females (her male offspring will have huge tale and will reproduce. Classical Pronzi scheme in animal world. It is theoretically possible, peacocks can all agree that flight is a good thing and they should choose male partner based on his flight, not his tail. However, it is not feasible. Similarly, humankind selected those who rest less and "works" for future more (here "works" includes "steal", "take part in raids", and, especially "organize raids"). The most active won competition within the groups. The group of the most active "builders of better tomorrow" won the evolutionary race in against other groups. Simply put they slaughtered natives and grubbed their land. Currently, there is no evolutionary benefit for humankind to work harder and harder. The results of harder work will anyway be destroyed in the economic (overproduction) crisis. In principle, humans could have agreed to balance their work and rest time... But in reality we are no better then peacocks in this delicate question. Hence, the struggle between carpe diem and "the builder of better tomorrow" will continue and topic-starter's question will touch people's hearts.

 

 

 

 

_____

 

* Analogy is not for everyone foolproof... But we don't have much options on this stage. There are copious procedures to solve problem (see "Materials and Methods" section in any scientific paper); but what standard methods do we have to notice/cognize and state/formulate a problem?

**Given the accuracy of gas consumption estimate (plus or minus two-fold) there is no point to copy all four digits in density constant.

*** For this discovery one needs to know how much water+food he consumes daily, divided by the weight of his body.

 

 

 

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No, the 7 year rule is not true. This can be shown by analysing the amount of carbon 14 that is incorporated in to DNA. Carbon 14 is a radioactive form of carbon that is present in the atmosphere such that any plants that absorb carbon dioxide will contain a ratio of carbon 12 to carbon 14 that matches that in the atmosphere. As animals then eat plants, they too will be made up of a ratio of carbon 12 to 14 that matches that in the plants they eat. Now, between 1955 and 1965 testing of atomic weapons caused a dramatic increase in carbon 14 levels in the atmosphere. In 1963 with the test treaty ban coming into force, the amount of carbon 14 in the atmosphere slowly reduced. Measuring the ratio of carbon 12 to carbon 14 in cerebral cortex neurons from people born before the cold war, he earliest was born in 1933, and died in 2000's, showed that the most of DNA in these neurons had carbon 14 levels that caresponded to the levels in the atmosphere before 1955, and that therefore DNA synthesis had occurred before 1955, ie during childhood. DNA synthesis during adulthood made up less than 1%. Therefore most of the carbon atoms that form your DNA in neurons as a child are the same atoms that make up your DNA throughout your entire life.

 

 

John

 

source...

 

 

Bhardwaj et al. (2006) Neocortical neurogenesis in humans is restricted to development. PNAS August 15, 2006 vol. 103 no. 33 12564-12568

http://www.pnas.org/...3/33/12564.full

 

I could see that test proving something if the body replaced cells by shedding them and re-growing them, but since they split into daughter cells for a variable number of generations, it seems the "original" cells could easily be disposed of within seven years and show no significant change in carbon-14 content. If they control for that, I'm very interested to see how they did it.

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