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Composition of the human body

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Not to be confused with Human anatomy.
The main elements that compose the human body are shown from most abundant (by mass) to least abundant.

The composition of the human body can be looked at from the point of view of either mass composition, or atomic composition. To illustrate both views, the adult male human body is approximately 57% water, and water is 11% hydrogen by mass but 67% by count of atoms (i.e. 67 atomic percent). Thus, most of the mass of the human body is oxygen, but most of the atoms in the human body are hydrogen atoms. Both mass-composition and atomic composition figures are given below (see pie graphs and table).

Body composition may also be analyzed in terms of molecular type (e.g., water, protein, connective tissue, fats (or lipids) apatite (in bones), carbohydrates (such as glycogen and glucose) and DNA. In terms of tissue type, the body may be analyzed into water, fat, 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 consist of bacteria (bacterial cells) residing in the normal human gastrointestinal tract.

Major, minor and trace elements

Pie charts of typical human body composition by percent of mass, and by percent of atomic composition (atomic percent).

Almost 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 are necessary to live. The remaining elements are trace elements, of which more than a dozen are thought to be necessary for life, or play a role in good health (e.g., fluorine, which hardens dental enamel but seems to have no other function).

An easy way to remember the six most essential elements in living organisms is CHNOPS (carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur).

Other elements and questionable human-required 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 bystander contaminants without function (examples: caesium, titanium), while many others are thought to be active toxics, 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. Functions have been proposed for trace amounts of cadmium and lead, although these are almost certainly toxic in amounts very much larger than normally found in the body. There is evidence that arsenic, an element normally considered a toxic in higher amounts, is essential in ultratrace quantities, even in mammals (rats, hamsters, goats).[1]

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. Bromine is used abundantly by some (though not all) lower organisms, and opportunistically in eosinophils in humans. It has recently been found to be necessary to collagen IV synthesis in humans (not yet confirmed).[2] Fluorine is used by a number of plants to manufacture toxins (see that element) but in humans only functions as a local (topical) hardening agent in tooth enamel, and not in an essential biological role.

Elemental composition list

Main article: Dietary element

The average 70 kg (150 lb) adult human body contains approximately 7×1027 atoms and contains at least detectable traces of 60 chemical elements.[3] About 29 of these elements are thought to play an active positive role in life and health in humans.[4]

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. 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.[5] 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.

Atomic number Element Fraction of mass[6][7][8][9][10][11] Mass (kg)[12] Atomic percent Positive health role in mammals[13] Negative effects of excess Group
8 Oxygen 0.65 43 24 Yes (e.g. water, electron acceptor) Reactive Oxygen Species 16
6 Carbon 0.18 16 12 Yes (organic compounds are hydrocarbon derivatives) 14
1 Hydrogen 0.10 7 62 Yes (e.g. water) 1
7 Nitrogen 0.03 1.8 1.1 Yes (e.g. DNA and amino acids) 15
20 Calcium 0.014 1.0 0.22 Yes (e.g. Calmodulin and Hydroxylapatite in bones) 2
15 Phosphorus 0.011 0.78 0.22 Yes (e.g. DNA and phosphorylation) 15
19 Potassium 2.5×10−3 0.14 0.033 Yes (e.g. Na+/K+-ATPase) 1
16 Sulfur 2.5×10−3 0.14 0.038 Yes (e.g.Cysteine, Methionine, Biotin, Thiamine) 16
11 Sodium 1.5×10−3 0.10 0.037 Yes (e.g. Na+/K+-ATPase) 1
17 Chlorine 1.5×10−3 0.095 0.024 Yes (e.g. Cl-transporting ATPase) 17
12 Magnesium 500×10−6 0.019 0.0070 Yes (e.g. binding to ATP and other nucleotides) 2
26 Iron* 60×10−6 0.0042 0.00067 Yes (e.g. Hemoglobin, Cytochromes) 8
9 Fluorine 37×10−6 0.0026 0.0012 Yes (topically hardens teeth) toxic in high amounts 17
30 Zinc 32×10−6 0.0023 0.00031 Yes (e.g. Zinc finger proteins) 12
14 Silicon 20×10−6 0.0010 0.0058 Yes (probable) 14
37 Rubidium 4.6×10−6 0.00068 0.000033 No (probable) 1
38 Strontium 4.6×10−6 0.00032 0.000033 Possible (suspected bone growth factor) 2
35 Bromine 2.9×10−6 0.00026 0.000030 Yes (not confirmed) Collagen IV crosslink synthetic cofactor.[2] 17
82 Lead 1.7×10−6 0.00012 0.0000045 No, probably (possible NMDA antagonist) toxic in higher amounts 14
29 Copper 1×10−6 0.000072 0.0000104 Yes (e.g. copper proteins) 11
13 Aluminum 870×10−9 0.000060 0.000015 No 13
48 Cadmium 720×10−9 0.000050 0.0000045 No, probably toxic in higher amounts 12
58 Cerium 570×10−9 0.000040 No
56 Barium 310×10−9 0.000022 0.0000012 No, probably toxic 2
50 Tin 240×10−9 0.000020 6.0×10−7 No, probably 14
53 Iodine 160×10−9 0.000020 7.5×10−7 Yes (e.g. thyroxine, triiodothyronine) 17
22 Titanium 130×10−9 0.000020 No 4
5 Boron 690×10−9 0.000018 0.0000030 Yes (probably) 13
34 Selenium 190×10−9 0.000015 4.5×10−8 Yes toxic in higher amounts 16
28 Nickel 140×10−9 0.000015 0.0000015 No, probably 10
24 Chromium 24×10−9 0.000014 8.9×10−8 Yes (not confirmed) 6
25 Manganese 170×10−9 0.000012 0.0000015 Yes (e.g. Mn-SOD) 7
33 Arsenic 260×10−9 0.000007 8.9×10−8 Yes in rats, hamsters, goats. Probably humans.[1] toxic in higher amounts 15
3 Lithium 31×10−9 0.000007 0.0000015 Yes, probably. Useful medically (mood stabilizer). toxic in higher amounts 1
80 Mercury 190×10−9 0.000006 8.9×10−8 No toxic 12
55 Caesium 21×10−9 0.000006 1.0×10−7 No 1
42 Molybdenum 130×10−9 0.000005 4.5×10−8 Yes (e.g. the molybdenum oxotransferases, Xanthine oxidase and Sulfite oxidase) 6
32 Germanium 5×10−6 No, probably 14
27 Cobalt 21×10−9 0.000003 3.0×10−7 Yes (cobalamin, B12) 9
51 Antimony 110×10−9 0.000002 No toxic 15
47 Silver 10×10−9 0.000002 No 11
41 Niobium 1600×10−9 0.0000015 No 5
40 Zirconium 6000×10−9 0.000001 3.0×10−7 No 4
57 Lanthanum 1370×10−9 8×10−7 No
52 Tellurium 120×10−9 7×10−7 No 16
31 Gallium 7×10−7 No 13
39 Yttrium 6×10−7 No 3
83 Bismuth 5×10−7 No (Useful in small amounts for gastrointestinal pain) 15
81 Thallium 5×10−7 No toxic 13
49 Indium 4×10−7 No 13
79 Gold 140×10−9 2×10−7 3.0×10−7 No 11
21 Scandium 2×10−7 No 3
73 Tantalum 2×10−7 No 5
23 Vanadium 260×10−9 1.1×10−7 1.2×10−8 Yes (?) (In humans, suggested osteo-metabolism (bone) growth factor) 5
90 Thorium 1×10−7 No toxic
92 Uranium 1×10−7 3.0×10−9 No toxic
62 Samarium 5.0×10−8 No
74 Tungsten 2.0×10−8 No 6
4 Beryllium 3.6×10−8 4.5×10−8 No toxic 2
88 Radium 3×10−14 1×10−17 No toxic 2

*Iron = ~3 g in men, ~2.3 g in women

Most of the elements needed for life are relatively common in the Earth's crust. There are exceptions: cobalt for instance makes up only about 25 parts per million of the Earth's crust but is essential for human life. Conversely most of the common elements are necessary for life. An exception is aluminum, 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.[14]Transferrins can bind aluminum.[15]

Essential elements on the periodic table

Periodic table highlighting dietary elements

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 Uut Fl Uup Lv Uus Uuo
 
  * 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
The four organic basic elements Quantity elements Essential trace elements Possible structural or functional role in mammals

Composition by molecule type

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:[17]

Molecule Percent of Mass Mol.Weight (daltons) Molecules Percent of Molecules
Water 65* 18* 1.74×1014 98.73
Other Inorganics 1.5 N/A 1.31×1012 0.74
Lipids 12 N/A 8.4×1011 0.475
Other Organics 0.4 N/A 7.7×1010 0.044
Protein 20 N/A 1.9×1010 0.011
RNA 1.0 N/A 5×107 3×10−5
DNA 0.1 1×1011 46* 3×10−11

*The amount of water is highly dependent on body composition and amount of fat. In adults in developed countries it averages ~53% water. 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.[5] DNA: A human cell also contains mitochondrial DNA. Sperm cells contain less mitochondrial DNA than other cells. A mammalian red blood cell normally contains no nucleus in adulthood, and thus no DNA. However, nucleated red blood cells, or NRBCs, are present in the fetal and neonatal circulations, and may appear in mature mammals when disease is present.

Materials and tissues

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, 90% of the cells in (or on) a human body are microbes, by number[18][19] (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

  1. ^ a b Anke M. Arsenic. In: Mertz W. ed., Trace elements in human and Animal Nutrition, 5th ed. Orlando, FL: Academic Press, 1986, 347-372; Uthus E.O., Evidency for arsenical essentiality, Environ. Geochem. Health, 1992, 14:54-56; Uthus E.O., Arsenic essentiality and factors affecting its importance. In: Chappell W.R, Abernathy C.O, Cothern C.R. eds., Arsenic Exposure and Health. Northwood, UK: Science and Technology Letters, 1994, 199-208.
  2. ^ a b McCall AS, Cummings CF, Bhave G, Vanacore R, Page-McCaw A, Hudson BG (2014). "Bromine Is an Essential Trace Element for Assembly of Collagen IV Scaffolds in Tissue Development and Architecture". Cell. 157 (6): 1380–92. doi:10.1016/j.cell.2014.05.009. PMID 24906154.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  3. ^ How many atoms are in the human body?
  4. ^ Ultratrace minerals. Authors: Nielsen, Forrest H. USDA, ARS Source: Modern nutrition in health and disease / editors, Maurice E. Shils ... et al.. Baltimore : Williams & Wilkins, c1999., p. 283-303. Issue Date: 1999 URI: [1]
  5. ^ a b See table 1. here
  6. ^ Thomas J. Glover, comp., Pocket Ref, 3rd ed. (Littleton: Sequoia, 2003), p. 324 (LCCN 2002-91021), which in
  7. ^ turn cites Geigy Scientific Tables, Ciba-Geigy Limited, Basel, Switzerland, 1984.
  8. ^ Chang, Raymond (2007). Chemistry, Ninth Edition. McGraw-Hill. p. 52. ISBN 0-07-110595-6.
  9. ^ Distribution of elements in the human body (by weight) Retrieved on 2007-12-06
  10. ^ Frausto Da Silva, J. J. R; Williams, R. J. P (2001-08-16). "The Biological Chemistry of the Elements: The Inorganic Chemistry of Life". ISBN 9780198508489. {{cite journal}}: Cite journal requires |journal= (help)
  11. ^ Zumdahl, Steven S. and Susan A. (2000). Chemistry, Fifth Edition. Houghton Mifflin Company. p. 894. ISBN 0-395-98581-1.)
  12. ^ J. Emsley, The Element, 3rd ed., Oxford: Clarendon Press, 1998.
  13. ^ Neilsen, cited
  14. ^ Aluminum Toxicity
  15. ^ Mizutani, K.; Mikami, B.; Aibara, S.; Hirose, M. (2005). "Structure of aluminium-bound ovotransferrin at 2.15 Å resolution". Acta Crystallographica Section D Biological Crystallography. 61 (12): 1636. doi:10.1107/S090744490503266X.
  16. ^ Douglas Fox, "The speed of life", New Scientist, No 2419, 1 November 2003.
  17. ^ Freitas Jr., Robert A. (1999). Nanomedicine,. Landes Bioscience. Tables 3–1 & 3–2. ISBN 1-57059-680-8. {{cite book}}: Unknown parameter |nopp= ignored (|no-pp= suggested) (help)
  18. ^ Glausiusz, Josie. "Your Body Is a Planet". Retrieved 2007-09-16.
  19. ^ Wenner, Melinda. "Humans Carry More Bacterial Cells than Human Ones". Retrieved 2010-10-09.
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