# Result of replacing all the water in a human body with "heavy water" **URL:** \ **Category:** Factual Questions\ **Created:** [March 3, 2004, 8:31am UTC](https://boards.straightdope.com/t/result-of-replacing-all-the-water-in-a-human-body-with-heavy-water/232273 "2004-03-03T08:31:54Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![OldFogey](https://avatars.discourse-cdn.com/v4/letter/o/a698b9/32.png) [@OldFogey](https://boards.straightdope.com/u/OldFogey)\ **Post date:** [March 3, 2004, 8:31am UTC](https://boards.straightdope.com/t/result-of-replacing-all-the-water-in-a-human-body-with-heavy-water/232273/1 "2004-03-03T08:31:54Z")
Has anyone done a study - or figured out theoretically - exactly what would happen to a human body if the water in it was replaced with heavy water? (Heavy water is water in which the hydrogen atoms/ions have a neutron in the nucleus along with the proton, making them “heavy hydrogen”.) I assume the resulting body would be heavier (by less than 10%), but since this change is at the atomic level would there be any of the usual problems associated with weight gain? I read in the 1970s that heavy water is one of the rarest naturally occurring substances in the world, and the cost of the stuff was something like $20,000 an ounce; what with inflation and all, I suspect the cost of actually doing a study like that to be sort of prohibitive. But has anyone figured out, theoretically at least, what would happen in such a case? ---
**Author:** ![Saranga](https://avatars.discourse-cdn.com/v4/letter/s/d6d6ee/32.png) [@Saranga](https://boards.straightdope.com/u/Saranga)\ **Post date:** [March 3, 2004, 9:06am UTC](https://boards.straightdope.com/t/result-of-replacing-all-the-water-in-a-human-body-with-heavy-water/232273/2 "2004-03-03T09:06:30Z")
Here’s a somewhat relevant SDStaff report: [Is Heavy Water dangerous?](http://www.straightdope.com/mailbag/mheavywater.html) ---
**Author:** ![j\_sum1](https://avatars.discourse-cdn.com/v4/letter/j/8baadc/32.png) [@j\_sum1](https://boards.straightdope.com/u/j_sum1)\ **Post date:** [March 3, 2004, 9:12am UTC](https://boards.straightdope.com/t/result-of-replacing-all-the-water-in-a-human-body-with-heavy-water/232273/3 "2004-03-03T09:12:50Z")
[Here’s](http://www.straightdope.com/mailbag/mheavywater.html) the straight dope according to **Q.E.D.** In particular note paragraph four. > [@](#): > > Despite the fact the light water and heavy water are chemically identical, heavy water is mildly toxic. How can this be? Since heavy water is heavier than normal water, the speed of chemical reactions involving it is altered somewhat, as is the strength of some types of bonds it forms. This affects certain cellular processes, notably mitosis, or cell division, due to the difference in binding energy in the hydrogen bonds needed to make certain proteins. Mouse studies have shown that drinking only heavy water along with normal feed eventually causes degeneration of tissues that need to replenish themselves frequently, and leads to cumulative damage from injuries that don’t heal as quickly. One study likens the effects to those suffered by chemotherapy patients. Heavy water toxicity manifests itself when about 50% of the water in the body has been replaced by D2O. Prolonged heavy water consumption can cause death. I think that mostly answers the question. My guess is that as well as being dead and setting off a few Geiger counters, you would probably sink in the pool as well. ---
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [March 3, 2004, 11:14am UTC](https://boards.straightdope.com/t/result-of-replacing-all-the-water-in-a-human-body-with-heavy-water/232273/4 "2004-03-03T11:14:21Z")
You wouldn’t be setting off any Geiger counters (well, no more than usual) - deuterium isn’t radioactive. You might be thinking of tritium. ---
**Author:** ![bizzwire](https://avatars.discourse-cdn.com/v4/letter/b/958977/32.png) [@bizzwire](https://boards.straightdope.com/u/bizzwire)\ **Post date:** [March 3, 2004, 11:51am UTC](https://boards.straightdope.com/t/result-of-replacing-all-the-water-in-a-human-body-with-heavy-water/232273/5 "2004-03-03T11:51:41Z")
for what it’s worth, according to my calculations (I’ve always wanted to use that phrase), if all the water in your body were replace with deuterium oxide, your weight would increase by a little over 11 %. ---
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [March 3, 2004, 12:43pm UTC](https://boards.straightdope.com/t/result-of-replacing-all-the-water-in-a-human-body-with-heavy-water/232273/6 "2004-03-03T12:43:01Z")
> [@bizzwire](#): > > for what it’s worth, according to my calculations (I’ve always wanted to use that phrase), if all the water in your body were replace with deuterium oxide, your weight would increase by a little over 11 %. Hmm. According to _my_ calculations, it’s a little less than that. Cecil says that D[sub]2[/sub]O has a density of 1.108g/cm[sup]3[/sup], so it is 10.8% heavier than normal water. Taking a ballpark figure of 70% of the body by mass being water, I’d say the new weight would be [(1.108 x 0.7) + 0.3] = 1.0756, or about a 7.6% increase in weight. Now, anyone care to volunteer to try this experiment with T[sub]2[/sub]O? ---
**Author:** ![Headcoat](https://avatars.discourse-cdn.com/v4/letter/h/6bbea6/32.png) [@Headcoat](https://boards.straightdope.com/u/Headcoat)\ **Post date:** [March 3, 2004, 2:30pm UTC](https://boards.straightdope.com/t/result-of-replacing-all-the-water-in-a-human-body-with-heavy-water/232273/7 "2004-03-03T14:30:40Z")
Where does heavy water occur naturally? ---
**Author:** ![Grey](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grey](https://boards.straightdope.com/u/Grey)\ **Post date:** [March 3, 2004, 2:39pm UTC](https://boards.straightdope.com/t/result-of-replacing-all-the-water-in-a-human-body-with-heavy-water/232273/8 "2004-03-03T14:39:32Z")
In water, and no I’m not being smart. Honest. 🙂 ---
**Author:** ![Grey](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grey](https://boards.straightdope.com/u/Grey)\ **Post date:** [March 3, 2004, 2:47pm UTC](https://boards.straightdope.com/t/result-of-replacing-all-the-water-in-a-human-body-with-heavy-water/232273/9 "2004-03-03T14:47:39Z")
Here’s a pdf paper by [Atomic Energy Canada on Heavy Water](http://www.cns-snc.ca/Bulletin/A_Miller_Heavy_Water.pdf). CANDU reactors use heavy water as opposed to regular water. ---
**Author:** ![Excalibre](https://avatars.discourse-cdn.com/v4/letter/e/898d66/32.png) [@Excalibre](https://boards.straightdope.com/u/Excalibre)\ **Post date:** [March 3, 2004, 3:21pm UTC](https://boards.straightdope.com/t/result-of-replacing-all-the-water-in-a-human-body-with-heavy-water/232273/10 "2004-03-03T15:21:02Z")
Incidentally, it doesn’t taste any different, but I do think it had a slightly different mouthfeel; it was very slightly viscous. This was also noticeable when we measured it in small quantities - 1 ml volumetric flasks and the like. Working in the chemistry lab was fun . . . ---
**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\ **Post date:** [March 3, 2004, 9:16pm UTC](https://boards.straightdope.com/t/result-of-replacing-all-the-water-in-a-human-body-with-heavy-water/232273/11 "2004-03-03T21:16:25Z")
> [@Q.E.D.](#): > > Despite the fact the light water and heavy water are chemically identical, heavy water is mildly toxic. How can this be? Since heavy water is heavier than normal water, the speed of chemical reactions involving it is altered somewhat, as is the strength of some types of bonds it forms. Isn’t this contradictory? That is, if heavy water has different reaction speeds and different bond energies, then it is by definition _not_ chemically identical to water. Unless “chemically identical” does not mean “having exactly the same chemical properties”. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [March 3, 2004, 9:23pm UTC](https://boards.straightdope.com/t/result-of-replacing-all-the-water-in-a-human-body-with-heavy-water/232273/12 "2004-03-03T21:23:21Z")
> [@Pleonast](#): > > Isn’t this contradictory? That is, if heavy water has different reaction speeds and different bond energies, then it is by definition _not_ chemically identical to water. Unless “chemically identical” does not mean “having exactly the same chemical properties”. Semantics, I suppose. I was using the phrase “chemically” to indicate that the electron structure–the primary determinant of the chemical nature of a substance–is identical. That is, the reaction products are the same for both. Admittedly, I could have been clearer on this point, but I don’t like to get too caught up in nitpicky details in my Staff Reports. 🙂