The composition of the human body can be looked at from several different points of view.
By mass, human cells consist of 65–90% water (H2O). Oxygen therefore contributes a majority of a human body's mass. Almost 99% of the mass of the human body is made up of the six elements oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus.
About 0.85% is composed of only five elements: potassium, sulfur, sodium, chlorine, and magnesium. All are necessary to life. The remaining elements are trace elements, of which more than a dozen are thought to be necessary for life, or play an active role in health (e.g., fluorine, which hardens dental enamel but seems to have no other function).
Note that not all elements which are found in the human body in trace quantities play a role in life. Some of these elements are thought to be simple bystander contaminants without function (examples: caesium, titanium), while many others are thought to be active toxins, depending on amount (cadmium, mercury, radioactives). The possible utility and toxicity of a few elements at levels normally found in the body (aluminum) is debated. Trace amounts of cadmium and lead have had functions suggested, but are almost certainly toxic in amounts normally found in the body. There is evidence that one element normally thought a toxin (arsenic) is essential in ultratrace quantities, even in mammals. Some elements that are clearly used in lower organisms and plants (arsenic, silicon, boron, nickel, vanadium) are probably needed by mammals also, but in far smaller doses. Two halogens used abundantly by lower organisms (fluorine and bromine) are presently known to be used by mammals only opportunistically. However, a general rule is that elements found in active biochemical use in lower organisms are often eventually found to be used in some way by higher organisms.
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The average 70 kg adult human body contains approximately 6.7 x 1027 atoms and is "composed of" 60 chemical elements. In this sense, "composed of" means that a trace of the element has been identified in the body. However, at the finest resolution, most objects on Earth (including the human body) contain measureable contaminating amounts of all of the 88 chemical elements which are detectable in nearly any soil on Earth. The number of elements thought to play an active positive role in life and augmentation of health in humans and other mammals, is about 24 or 25.[1]
The relative amounts of each element vary by individual. The numbers in the table are averages of different numbers reported by different references.
The human body is ~70% water, which is ~11% hydrogen by mass but ~66% hydrogen by atomic percent.
Atomic number | Element | Percent of Mass[2][3][4][5] | Mass (kg)[6] | Atomic percent | Atoms | Positive health role in mammals[7] | Group |
---|---|---|---|---|---|---|---|
8 | Oxygen | 65 | 43 | 24 | 1.61e27 | Yes (e.g. water) | 16 |
6 | Carbon | 18 | 16 | 12 | 8.03e26 | Yes (organic compounds are hydrocarbon derivatives) | 14 |
1 | Hydrogen | 10 | 7 | 63 | 4.22e27 | Yes (e.g. water) | 1 |
7 | Nitrogen | 3 | 1.8 | 0.58 | 3.9e25 | Yes (e.g. DNA and amino acids) | 15 |
20 | Calcium | 1.4 | 1.0 | 0.24 | 1.6e25 | Yes (e.g. Calmodulin and Hydroxylapatite in bones) | 2 |
15 | Phosphorus | 1.1 | 7.8e-1 | 0.14 | 9.6e24 | Yes (e.g. DNA and phosphorylation) | 15 |
19 | Potassium | 0.25 | 1.4e-1 | 0.033 | 2.2e24 | Yes (e.g. Na+/K+-ATPase) | 1 |
16 | Sulfur | 0.25 | 0.140 | 0.038 | 2.6e24 | Yes (e.g. Cysteine and Methionine) | 16 |
11 | Sodium | 0.15 | 0.100 | 0.037 | 2.5e24 | Yes (e.g. Na+/K+-ATPase) | 1 |
17 | Chlorine | 0.15 | 0.095 | 0.024 | 1.6e24 | Yes (e.g. Cl-transporting ATPase) | 17 |
12 | Magnesium | 0.05 | 0.019 | 0.0070 | 4.7e23 | Yes (e.g. binding to ATP) | 2 |
26 | Iron* | 0.006 | 0.0042 | 0.00067 | 4.5e22 | Yes (e.g. Hemoglobin) | 8 |
9 | Fluorine | 0.0037 | 0.0026 | 0.0012 | 8.3e22 | Yes/No (topically hardens teeth) | 17 |
30 | Zinc | 0.0032 | 0.0023 | 0.00031 | 2.1e22 | Yes (e.g. Zinc finger proteins) | 12 |
14 | Silicon | 0.002 | 0.0010 | 0.0058 | 3.9e23 | Yes (probable) | 14 |
37 | Rubidium | 0.00046 | 0.00068 | 0.000033 | 2.2e21 | No (?) | 1 |
38 | Strontium | 0.00046 | 0.00032 | 0.000033 | 2.2e21 | No (?) | 2 |
35 | Bromine | 0.00029 | 0.00026 | 0.000030 | 2.0e21 | No (?) | 17 |
82 | Lead | 0.00017 | 0.00012 | 0.0000045 | 3e20 | No (?) (toxin in higher amounts) | 14 |
29 | Copper | 0.0001 | 0.000072 | 0.0000104 | 7e20 | Yes (e.g. copper proteins) | 11 |
13 | Aluminium | 0.000087 | 0.000060 | 0.000015 | 1.0e21 | No(?) (toxin?) | 13 |
48 | Cadmium | 0.000072 | 0.000050 | 0.0000045 | 3e20 | No(?) (toxin in higher amounts) | 12 |
58 | Cerium | 0.000057 | 0.000040 | No | |||
56 | Barium | 0.000031 | 0.000022 | 0.0000012 | 8e19 | No (toxin?) | 2 |
50 | Tin | 0.000024 | 0.000020 | 6.0e-7 | 4e19 | No(?) | 14 |
53 | Iodine | 0.000016 | 0.000020 | 7.5e-7 | 5e19 | Yes (e.g. Thyroxine) | 17 |
22 | Titanium | 0.000013 | 0.000020 | No | 4 | ||
5 | Boron | 0.000069 | 0.000018 | 0.0000030 | 2e20 | Yes (probable) | 13 |
34 | Selenium | 0.000019 | 0.000015 | 4.5e-8 | 3e18 | Yes | 16 |
28 | Nickel | 0.000014 | 0.000015 | 0.0000015 | 1e20 | Yes(e.g. urease) | 10 |
24 | Chromium | 0.0000024 | 0.000014 | 8.9e-8 | 6e18 | Yes (not confirmed) | 6 |
25 | Manganese | 0.000017 | 0.000012 | 0.0000015 | 1e20 | Yes (e.g. Mn-SOD) | 7 |
33 | Arsenic | 0.000026 | 0.000007 | 8.9e-8 | 6e18 | Yes (not confirmed). Toxic in higher amounts | 15 |
3 | Lithium | 0.0000031 | 0.000007 | 0.0000015 | 1e20 | Yes (not confirmed). Toxic in high amounts. Useful medically (mood stabilizer). | 1 |
80 | Mercury | 1.9e-5 | 0.000006 | 8.9e-8 | 6e18 | No (toxin) | 12 |
55 | Caesium | 0.0000021 | 6e-6 | 1.0e-7 | 7e18 | No | 1 |
42 | Molybdenum | 0.000013 | 5e-6 | 4.5e-8 | 3e18 | Yes (e.g. the molybdenum oxotransferases Xanthine oxidase and Sulfite oxidase | 6 |
32 | Germanium | 0.000005 | No (?) | 14 | |||
27 | Cobalt | 0.0000021 | 0.000003 | 3.0e-7 | 2e19 | Yes (e.g. vitamin B12) | 9 |
51 | Antimony | 0.000011 | 0.000002 | No | 15 | ||
47 | Silver | 0.000001 | 0.000002 | No (toxin) | 11 | ||
41 | Niobium | 0.00016 | 0.0000015 | No | 5 | ||
40 | Zirconium | 0.0006 | 0.000001 | 3.0e-7 | 2e19 | No | 4 |
57 | Lanthanum | 8e-7 | No | ||||
52 | Tellurium | 0.000012 | 7e-7 | No | 16 | ||
31 | Gallium | 7e-7 | No | 13 | |||
39 | Yttrium | 6e-7 | No | 3 | |||
83 | Bismuth | 5e-7 | No | 15 | |||
81 | Thallium | 5e-7 | No (toxin) | 13 | |||
49 | Indium | 4e-7 | No | 13 | |||
79 | Gold | 0.000014 | 2e-7 | 3.0e-7 | 2e19 | No | 11 |
21 | Scandium | 2e-7 | No | 3 | |||
73 | Tantalum | 2e-7 | No | 5 | |||
23 | Vanadium | 0.000026 | 1.1e-7 | 1.2e-8 | 8e17 | Yes (not confirmed) | 5 |
90 | Thorium | 1e-7 | No (toxin) | ||||
92 | Uranium | 1.3e-7 | 1e-7 | 3.0e-9 | 2e17 | No (toxin) | |
62 | Samarium | 5.0e-8 | No | ||||
74 | Tungsten | 2.0e-8 | No | 6 | |||
4 | Beryllium | 5e-9 | 3.6e-8 | 4.5e-8 | 3e18 | No | 2 |
88 | Radium | 1e-17 | 3e-14 | 1e-17% | 8e10 | No (toxin) | 2 |
*Iron = ~3 g in men, ~2.3 g in women
The elements needed for life are relatively common in the Earth's crust, and conversely most of the common elements are necessary for life. An exception is aluminium, which is the third most common element in the Earth's crust (after oxygen and silicon), but seems to serve no function in living cells. Rather, it is harmful in large amounts. Transferrins can bind aluminium.[8]
Periodic table highlighting dietary elements[9]
H | He | |||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Li | Be | B | C | N | O | F | Ne | |||||||||||
Na | Mg | Al | Si | P | S | Cl | Ar | |||||||||||
K | Ca | Sc | Ti | V | Cr | Mn | Fe | Co | Ni | Cu | Zn | Ga | Ge | As | Se | Br | Kr | |
Rb | Sr | Y | Zr | Nb | Mo | Tc | Ru | Rh | Pd | Ag | Cd | In | Sn | Sb | Te | I | Xe | |
Cs | Ba | La | * | Hf | Ta | W | Re | Os | Ir | Pt | Au | Hg | Tl | Pb | Bi | Po | At | Rn |
Fr | Ra | Ac | ** | Rf | Db | Sg | Bh | Hs | Mt | Ds | Rg | Cn | Uut | Uuq | Uup | Uuh | Uus | Uuo |
* | Ce | Pr | Nd | Pm | Sm | Eu | Gd | Tb | Dy | Ho | Er | Tm | Yb | Lu | ||||
** | Th | Pa | U | Np | Pu | Am | Cm | Bk | Cf | Es | Fm | Md | No | Lr |
The four organic basic elements | Quantity elements | Essential trace elements | Suggested function from biochemistry and handling but no identified biological function in humans |
The composition can also be expressed in terms of chemicals, such as:
The composition of the human body can be viewed on an atomic and molecular scale as shown in this article.
The estimated gross molecular contents of a typical 20-micrometre human cell is as follows:[11]
Molecule | Percent of Mass | Mol.Weight (daltons) | Molecules | Percent of Molecules |
---|---|---|---|---|
Water | 65* | 18* | 1.74e14* | 98.73* |
Other Inorganics | 1.5 | N/A | 1.31e12 | 0.74 |
Lipids | 12 | N/A | 8.4e11 | 0.475 |
Other Organics | 0.4 | N/A | 7.7e10 | 0.044 |
Protein | 20 | N/A | 1.9e10 | 0.011 |
RNA | 1.0 | N/A | 5e7 | 3e-5 |
DNA | 0.1 | 1e11 | 46* | 3e-11 |
Water: Obviously the amount of water is highly dependent on the level of hydration. DNA: A human cell also contains mitochondrial DNA. Sperm cells contain less mitochondrial DNA than other cells. A mammalian red blood cell contains no nucleus and thus no DNA.
Body composition can also be expressed in terms of various types of material, such as:
There are many species of bacteria and other microorganisms that live on or inside the healthy human body. In fact, 90% of the cells in (or on) a human body are microbes, by number[12][13] (much less by mass or volume). Some of these symbionts are necessary for our health. Those that neither help nor harm us are called commensal organisms.