# Elements (Human)

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 146550.  Tue Feb 13, 2007 1:43 pm We are made up of mostly 13 elements

 146618.  Tue Feb 13, 2007 5:23 pm .Last edited by Lucifers_Lady on Fri Apr 04, 2008 6:08 pm; edited 1 time in total

146622.  Tue Feb 13, 2007 5:37 pm

Over half the body mass is oxygen. Since:

 Wikipedia wrote: In men about 72% of the body mass is water. This value is about 68% in women due to a higher proportion of body fat. This is the total body water.

... and 16/18 of the mass of a water molecule is oxygen. Thus, in men, 64% of the body mass is oxygen, and in women, the figure is 60%.

With regards to the other 12 elements, it's fairly arbitrary which are the "main" elements. Since 99% of the body is made up of six elements (oxygen, nitrogen, hydrogen, carbon, calcium and phosphorous), I'd be tempted to say that these were the "main" elements.

The elements found on that Nottingham University link in the original post are just ones which, from what I can gather, need to be known by nurses. As interesting as it is (although somewhat irritating in that two elements fit some of the definitions!), I wouldn't use it as a claim that there are 13 main elements in the body.

S: Wikipedia - Body Water
S: Wikipedia - Abundance of Chemical Elements

146625.  Tue Feb 13, 2007 6:02 pm

In the book Why Don't Penguins' Feet Freeze? (a New Scientist book) the question What chemical formula would accurately describe an adult human being, in terms of the relative distribution of elements (including pollutants)? is asked.
The following is an excerpt of one of the answers:

 Quote: If a human body were broken into single atoms, we would arrive at an empirical formula: H15750 N310 O6500 C2250 Ca63 P48 K15 S15 Na10 Cl6 Mg3 Fe1.

... I make that to be twelve.

 146727.  Wed Feb 14, 2007 4:42 am It's an incredibly arbitrary number. There are far more elements in the body than those twelve. For example, fluorine is found in your teeth and bones, selenium protects your tissues from being attacked by oxygen, and copper is found in a variety of enzymes. This page contains a section showing the abundance of different elements in the body, and suggests that all but a little over 0.7% of the body is made up of Oxygen, Carbon, Hydrogen, Nitrogen, Calcium, Phosphorus, Potassium, Sulphur, Sodium and Magnesium. This gives two possible values for how many "main" elements there are in the body. Campbell and Farrell appear to give 13 main elements, although it would be necessary to read the original research paper to prove they didn't include more. Chang, however, gives 18 elements, of which only 11 are present in the body in a percentage of more than 0.05% by mass.

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