Composition of the human body

Body composition may be analyzed in various ways. This can be done in terms of the chemical elements present, or by molecular type e.g., water, protein, fats (or lipids), hydroxylapatite (in bones), carbohydrates (such as glycogen and glucose) and DNA. In terms of tissue type, the body may be analyzed into water, fat, connective tissue, muscle, bone, etc. In terms of cell type, the body contains hundreds of different types of cells, but notably, the largest number of cells contained in a human body (though not the largest mass of cells) are not human cells, but bacteria residing in the normal human gastrointestinal tract.

Elements

The main elements that compose the human body molecules (including water) can be summarized as CHNOPS.
Element Symbol percent
mass
percent
atoms
Oxygen O 65.0 24.0
Carbon C 18.5 12.0
Hydrogen H 10 62.0
Nitrogen N 3.2 1.1
Calcium Ca 1.5 0.22
Phosphorus P 1.0 0.22
Potassium K 0.4 0.03
Sulfur S 0.3 0.038
Sodium Na 0.2 0.037
Chlorine Cl 0.2 0.024
Magnesium Mg 0.1 0.015
All others < 0.1 < 0.3
Pie charts of typical human body composition by percent of mass, and by percent of atomic composition (atomic percent).

About 99% of the mass of the human body is made up of six elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. Only about 0.85% is composed of another five elements: potassium, sulfur, sodium, chlorine, and magnesium. All 11 are necessary for life. The remaining elements are trace elements, of which more than a dozen are thought on the basis of good evidence to be necessary for life.[1] All of the mass of the trace elements put together (less than 10 grams for a human body) do not add up to the body mass of magnesium, the least common of the 11 non-trace elements.

With approx 1 kg of phosphorus, valued at around 300 USD/kg, this makes up the highest part of the body's intrinsic value.[2]

Other elements

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 common contaminants without function (examples: caesium, titanium), while many others are thought to be active toxins, depending on amount (cadmium, mercury, lead, radioactives). In humans, arsenic is toxic, and its levels in foods and dietary supplements are closely monitored to reduce or eliminate its intake.[3]

Some elements (silicon, boron, nickel, vanadium) are probably needed by mammals also, but in far smaller doses. Bromine is used abundantly by some (though not all) lower organisms, and opportunistically in eosinophils in humans. One study has indicated bromine to be necessary to collagen IV synthesis in humans.[4] Fluorine is used by a number of plants to manufacture toxins but only functions in humans as a local topical hardening agent in tooth enamel.[5]

Elemental composition list

The average 70 kg (150 lb) adult human body contains approximately 7×1027 atoms and contains at least detectable traces of 60 chemical elements.[6] About 29 of these elements are thought to play an active positive role in life and health in humans.[7]

The relative amounts of each element vary by individual, mainly due to differences in the proportion of fat, muscle and bone in their body. Persons with more fat will have a higher proportion of carbon and a lower proportion of most other elements (the proportion of hydrogen will be about the same). The numbers in the table are averages of different numbers reported by different references.

The adult human body averages ~53% water.[8] This varies substantially by age, sex, and adiposity. In a large sample of adults of all ages and both sexes, the figure for water fraction by weight was found to be 48 ±6% for females and 58 ±8% water for males.[9] Water is ~11% hydrogen by mass but ~67% hydrogen by atomic percent, and these numbers along with the complementary % numbers for oxygen in water, are the largest contributors to overall mass and atomic composition figures. Because of water content, the human body contains more oxygen by mass than any other element, but more hydrogen by atom-fraction than any element.

The elements listed below as "Essential in humans" are those listed by the (US) Food and Drug Administration as essential nutrients,[10] as well as six additional elements: oxygen, carbon, hydrogen, and nitrogen (the fundamental building blocks of life on Earth), sulfur (essential to all cells) and cobalt (a necessary component of vitamin B12). Elements listed as "Possibly" or "Probably" essential are those cited by the National Research Council (United States) as beneficial to human health and possibly or probably essential.[11]

Atomic numberElementFraction of mass
[12][13][14][15][16][17]
Mass (kg)[18]Atomic percentEssential in humans[19]!!Negative effects of excessGroup
8Oxygen0.654524Yes (e.g. water, electron acceptor)[20]Reactive oxygen species16
6Carbon0.181312Yes[20] (organic compounds)14
1Hydrogen0.10762Yes[20] (e.g. water)Acidosis1
7Nitrogen0.031.81.1Yes[20] (e.g. DNA and amino acids)15
20Calcium0.0141.00.22Yes[20][21][22] (e.g. Calmodulin and Hydroxylapatite in bones)Hypercalcaemia2
15Phosphorus0.0110.780.22Yes[20][21][22] (e.g. DNA, Phospholipids and Phosphorylation)Hyperphosphatemia15
19Potassium2.0×10−30.140.033Yes[20][21] (e.g. Na+/K+-ATPase)Hyperkalemia1
16Sulfur2.5×10−30.140.038Yes[20] (e.g. Cysteine, Methionine, Biotin, Thiamine)Sulfhemoglobinemia16
11Sodium1.5×10−30.100.037Yes[21] (e.g. Na+/K+-ATPase)Hypernatremia1
17Chlorine1.5×10−30.0950.024Yes[21][22] (e.g. Cl-transporting ATPase)Hyperchloremia17
12Magnesium500×10−60.0190.0070Yes[21][22] (e.g. binding to ATP and other nucleotides)Hypermagnesemia2
26Iron*60×10−60.00420.00067Yes[21][22] (e.g. Hemoglobin, Cytochromes)Iron overload8
9Fluorine37×10−60.00260.0012Yes (AUS, NZ),[23] No (US, EU),[24][25] Maybe (WHO)[26]Fluorine: Highly toxic

Fluoride: Toxic in high amounts

17
30Zinc32×10−60.00230.00031Yes[21][22] (e.g. Zinc finger proteins)Zinc toxicity12
14Silicon20×10−60.00100.0058Probably[27]14
31Gallium4.9×10−60.00070.00093NoGallium halide poisoning[28]13
37Rubidium4.6×10−60.000680.000033NoPotassium replacement1
38Strontium4.6×10−60.000320.000033——Calcium replacement2
35Bromine2.9×10−60.000260.000030——Bromism17
82Lead1.7×10−60.000120.0000045NoLead poisoning14
29Copper1×10−60.0000720.0000104Yes[21][22] (e.g. copper proteins)Copper toxicity11
13Aluminium870×10−90.0000600.000015NoAluminium poisoning13
48Cadmium720×10−90.0000500.0000045NoCadmium poisoning12
58Cerium570×10−90.000040No
56Barium310×10−90.0000220.0000012Notoxic in higher amounts2
50Tin240×10−90.0000206.0×10−7No14
53Iodine160×10−90.0000207.5×10−7Yes[21][22] (e.g. thyroxine, triiodothyronine)Iodine-induced Hyperthyroidism[29]17
22Titanium130×10−90.000020No4
5Boron690×10−90.0000180.0000030Probably[11][30]13
34Selenium190×10−90.0000154.5×10−8Yes[21][22] (e.g. selenocysteine)Selenium toxicity16
28Nickel140×10−90.0000150.0000015Notoxic10
24Chromium24×10−90.0000148.9×10−8Yes[21][22]6
25Manganese170×10−90.0000120.0000015Yes[21][22] (e.g. Mn-SOD)7
33Arsenic260×10−90.0000078.9×10−8No[3]Arsenic poisoning15
3Lithium31×10−90.0000070.0000015Yes (intercorrelated with the functions of several enzymes, hormones and vitamins)Lithium toxicity1
80Mercury190×10−90.0000068.9×10−8NoMercury poisoning12
55Caesium21×10−90.0000061.0×10−7No1
42Molybdenum130×10−90.0000054.5×10−8Yes[21][22] (e.g. the molybdenum oxotransferases, Xanthine oxidase and Sulfite oxidase)6
32Germanium5×10−6No14
27Cobalt21×10−90.0000033.0×10−7Yes (e.g. Cobalamin/Vitamin B12)[31][32]9
44Ruthenium22×10−90.000007No [33]8
51Antimony110×10−90.000002Notoxic15
47Silver10×10−90.000002No11
41Niobium1600×10−90.0000015No5
40Zirconium6×10−60.0000013.0×10−7No4
57Lanthanum1370×10−98×10−7No
52Tellurium120×10−97×10−7No16
39Yttrium6×10−7No3
83Bismuth5×10−7No15
81Thallium5×10−7Nohighly toxic13
49Indium4×10−7No13
79Gold3×10−92×10−73.0×10−7Nouncoated nanoparticles possibly genotoxic[34][35][36]11
21Scandium2×10−7No3
73Tantalum2×10−7No5
23Vanadium260×10−91.1×10−71.2×10−8Possibly[11] (suggested osteo-metabolism (bone) growth factor)5
90Thorium1×10−7Notoxic, radioactive
92Uranium1×10−73.0×10−9Notoxic, radioactive
62Samarium5.0×10−8No
74Tungsten2.0×10−8No6
4Beryllium3.6×10−84.5×10−8Notoxic in higher amounts2
88Radium3×10−141×10−17Notoxic, radioactive2

*Iron = ~3 g in males, ~2.3 g in females

Of the 94 naturally occurring chemical elements, 61 are listed in the table above. Of the remaining 33, it is not known how many occur in the human body.

Most of the elements needed for life are relatively common in the Earth's crust. Aluminium, the third most common element in the Earth's crust (after oxygen and silicon), serves no function in living cells, but is toxic in large amounts, depending on its physical and chemical forms and magnitude, duration, frequency of exposure, and how it was absorbed by the human body.[37] Transferrins can bind aluminium.[38]

Periodic table

Nutritional elements in the periodic table[39]
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 * Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Fr Ra ** Lr Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og
 
  * La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb
  ** Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No
Legend:
  Quantity elements
  Essential trace elements
  Deemed essential trace element by U.S., not by European Union
  Suggested function from deprivation effects or active metabolic handling, but no clearly-identified biochemical function in humans
  Limited circumstantial evidence for trace benefits or biological action in mammals
  No evidence for biological action in mammals, but essential in some lower organisms.
(In the case of lanthanum, the definition of an essential nutrient as being indispensable and irreplaceable is not completely applicable due to the extreme similarity of the lanthanides. The stable early lanthanides up to Sm are known to stimulate the growth of various lanthanide-using organisms.)[40]

Molecules

The composition of the human body expressed in terms of chemicals:

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:[42]

MoleculePercent of massMol. weight (daltons)MoleculesPercent of molecules
Water65181.74×101498.73
Other inorganics1.5N/A1.31×10120.74
Lipids12N/A8.4×10110.475
Other organics0.4N/A7.7×10100.044
Protein20N/A1.9×10100.011
RNA1.0N/A5×1073×10−5
DNA0.11×1011463×10−11

Tissues

The main cellular components of the human body.[43]
Cell type  % mass  % cell count
Erythrocytes (red blood cells) 4.2 85.0
Muscle cells 28.6 0.001
Adipocytes (fat cells) 18.6 0.2
Other cells 14.3 14.8
Extracellular components 34.3 -

Body composition can also be expressed in terms of various types of material, such as:

Composition by cell type

There are many species of bacteria and other microorganisms that live on or inside the healthy human body. In fact, there are roughly as many microbial as human cells in the human body by number.[44] [45] [46] [47] (much less by mass or volume). Some of these symbionts are necessary for our health. Those that neither help nor harm humans are called commensal organisms.

See also

References

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