# Do I still have most of the atoms I was born with? **URL:** \ **Category:** Factual Questions\ **Created:** [March 2, 2018, 10:19pm UTC](https://boards.straightdope.com/t/do-i-still-have-most-of-the-atoms-i-was-born-with/809932 "2018-03-02T22:19:31Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![Grrr](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/grrr/32/146_2.png) [@Grrr](https://boards.straightdope.com/u/Grrr)\ **Post date:** [March 2, 2018, 10:19pm UTC](https://boards.straightdope.com/t/do-i-still-have-most-of-the-atoms-i-was-born-with/809932/1 "2018-03-02T22:19:31Z")
I get that we loose some through skin shedding, hair falling out, body fluids, etc… But do we keep most of the atoms we are born with? Or do they all get replaced through the passage of time? ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [March 2, 2018, 10:40pm UTC](https://boards.straightdope.com/t/do-i-still-have-most-of-the-atoms-i-was-born-with/809932/2 "2018-03-02T22:40:03Z")
Most of the atoms you were born with have been lost. However, some of them in the central nervous system and the lens of your eye are probably still there. Of course, since you were born your mass has increased by 30-40 times or more so that most of your atoms would be new anyway. [Most cell types have a life span of only a few days to months.](http://book.bionumbers.org/how-quickly-do-different-cells-in-the-body-replace-themselves/) When they die, they are replaced by new cells probably built up in part from new atoms derived from your food (although atoms recycled from cells that have died could also be incorporated). Nerve cells, lens cells, and oocytes (egg cells) last a lifetime. (Of course, any new cells that were not present at birth are made of new atoms.) While there will be some cell repair that will replace atoms, they probably contain many of their original atoms. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [March 3, 2018, 1:03am UTC](https://boards.straightdope.com/t/do-i-still-have-most-of-the-atoms-i-was-born-with/809932/3 "2018-03-03T01:03:40Z")
Great answer. Great cite. ETA: Great site at cite. A keeper. ---
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [March 3, 2018, 10:30am UTC](https://boards.straightdope.com/t/do-i-still-have-most-of-the-atoms-i-was-born-with/809932/4 "2018-03-03T10:30:59Z")
How about bones? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [March 3, 2018, 1:22pm UTC](https://boards.straightdope.com/t/do-i-still-have-most-of-the-atoms-i-was-born-with/809932/5 "2018-03-03T13:22:56Z")
Even if you have some of your original cells, each cell is also continually exchanging material with its environment: Taking in glucose, oxygen, and amino acids, and releasing water, carbon dioxide, and proteins. And some of those processes involve swapping atoms, not just releasing the same atoms that were brought in for the raw materials. ---
**Author:** ![Iggy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/iggy/32/3364_2.png) [@Iggy](https://boards.straightdope.com/u/Iggy)\ **Post date:** [March 3, 2018, 1:35pm UTC](https://boards.straightdope.com/t/do-i-still-have-most-of-the-atoms-i-was-born-with/809932/6 "2018-03-03T13:35:23Z")
> [@Quartz](#): > > How about bones? Bones are constantly being torn down and rebuilt. Probably safe to presume that most of the atoms that were present in your bones when you were born have long since been replaced. ---
**Author:** ![StarvingButStrong](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/starvingbutstrong/32/335_2.png) [@StarvingButStrong](https://boards.straightdope.com/u/StarvingButStrong)\ **Post date:** [March 3, 2018, 9:11pm UTC](https://boards.straightdope.com/t/do-i-still-have-most-of-the-atoms-i-was-born-with/809932/7 "2018-03-03T21:11:33Z")
I’m sure I’ve read stories about radioactive isotopes accumulating in bodies. Is that just alarmism, then? Or is it like, this particular atom stops being in Cell #XXXX but after that cell dies and gets torn down, Cell #YYYYY grabs it up to reuse it? ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [March 3, 2018, 9:19pm UTC](https://boards.straightdope.com/t/do-i-still-have-most-of-the-atoms-i-was-born-with/809932/8 "2018-03-03T21:19:29Z")
> [@StarvingButStrong](#): > > I’m sure I’ve read stories about radioactive isotopes accumulating in bodies. Is that just alarmism, then? Or is it like, this particular atom stops being in Cell #XXXX but after that cell dies and gets torn down, Cell #YYYYY grabs it up to reuse it? Depends on the isotope. One of the radioactive isotopes of greatest concern is [Strontium-90.](https://en.wikipedia.org/wiki/Strontium-90) It mimics calcium and so is deposited in bone. Because bone is constantly being torn down and rebuilt is exactly why it gets deposited. But once bone is deposited it may be a while before that particular part is recycled. The average half-life of Strontium-90 in the body is estimated at 18 years, in which time it can do a lot of damage. The cite in my first posts mentions that the life span of various cell types has been estimated by tracking the C14 deposited in cells by atmospheric nuclear testing before the Test-ban Treaty. ---
**Author:** ![StarvingButStrong](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/starvingbutstrong/32/335_2.png) [@StarvingButStrong](https://boards.straightdope.com/u/StarvingButStrong)\ **Post date:** [March 3, 2018, 9:54pm UTC](https://boards.straightdope.com/t/do-i-still-have-most-of-the-atoms-i-was-born-with/809932/9 "2018-03-03T21:54:05Z")
Interesting, thank you. Now I remember that my father had some test that involved a radioactive isotope – related to a heart problem, I don’t remember/never knew the details – and for a while afterwards his, uh, excreta was collected for disposal outside of the normal plumbing system. I guess it only took a few days for his body to eliminate all of it. Or maybe whatever was used had a really short half-life. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [March 3, 2018, 10:24pm UTC](https://boards.straightdope.com/t/do-i-still-have-most-of-the-atoms-i-was-born-with/809932/10 "2018-03-03T22:24:13Z")
There are two half-lives talked about for medical isotopes: The physical half-life and the biological one. The physical one is how long it takes for the element to undergo radioactive decay, while the biological one is how long it takes for it to leave the body. Sometimes one is much shorter than the other, in which case that one is much more relevant, and sometimes they’re comparable, in which case you get a total effective half-life that’s shorter than either. ---
**Author:** ![Buck\_Godot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/buck_godot/32/6573_2.png) [@Buck\_Godot](https://boards.straightdope.com/u/Buck_Godot)\ **Post date:** [March 5, 2018, 6:23pm UTC](https://boards.straightdope.com/t/do-i-still-have-most-of-the-atoms-i-was-born-with/809932/11 "2018-03-05T18:23:04Z")
[78% of your body was water when you were born](https://water.usgs.gov/edu/propertyyou.html). This water is going in and out of your cells through diffusion all the time, passing into the blood stream where it is excreted and replaced with new fluids as you drink, so I doubt that there are very many of your original water atoms left. ---
**Author:** ![Tom\_Tildrum](https://avatars.discourse-cdn.com/v4/letter/t/e95f7d/32.png) [@Tom\_Tildrum](https://boards.straightdope.com/u/Tom_Tildrum)\ **Post date:** [March 5, 2018, 6:30pm UTC](https://boards.straightdope.com/t/do-i-still-have-most-of-the-atoms-i-was-born-with/809932/12 "2018-03-05T18:30:46Z")
That gum you swallowed as a kid might still be in there. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [March 5, 2018, 6:34pm UTC](https://boards.straightdope.com/t/do-i-still-have-most-of-the-atoms-i-was-born-with/809932/13 "2018-03-05T18:34:35Z")
> [@Buck\_Godot](#): > > [78% of your body was water when you were born](https://water.usgs.gov/edu/propertyyou.html). This water is going in and out of your cells through diffusion all the time, passing into the blood stream where it is excreted and replaced with new fluids as you drink, so I doubt that there are very many of your original water atoms left. That brings up another question–once the water molecules leave your body, they reenter the hydrological cycle. So around how many of those molecules (or atoms) can you expect to consume again later in life? ---
**Author:** ![chorpler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chorpler/32/2888_2.png) [@chorpler](https://boards.straightdope.com/u/chorpler)\ **Post date:** [March 7, 2018, 7:39am UTC](https://boards.straightdope.com/t/do-i-still-have-most-of-the-atoms-i-was-born-with/809932/14 "2018-03-07T07:39:51Z")
> [@Darren\_Garrison](#): > > That brings up another question–once the water molecules leave your body, they reenter the hydrological cycle. So around how many of those molecules (or atoms) can you expect to consume again later in life? Randall Munroe had a “What If” column that touched on this a little … [ah, here it is](https://what-if.xkcd.com/74/), the “Soda Planet” column. His conclusion was that most of the water molecules we drink haven’t ever been inside another person, but they’ve all been through many dinosaurs. ETA: I forgot to mention that he also says “On the other hand, it’s just about guaranteed that _some_ of the water molecules in any mouthful have been drunk by someone else.”