Body composition may be analyzed in various ways. This can be done in terms of the chemical elements present, or by molecular structure 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.
| scope=col | Element | scope=col | Symbol | scope=col | percent mass | scope=col | percent atoms | |
|---|---|---|---|---|---|---|---|---|
| Oxygen | O | 65.0 | 24.0 | |||||
| Carbon | C | 18.5 | 12.0 | |||||
| Hydrogen | H | 9.5 | 62.0 | |||||
| Nitrogen | N | 2.6 | 1.1 | |||||
| Calcium | Ca | 1.3 | 0.22 | |||||
| Phosphorus | P | 0.6 | 0.22 | |||||
| Sulfur | S | 0.3 | 0.038 | |||||
| Potassium | K | 0.2 | 0.03 | |||||
| Sodium | Na | 0.2 | 0.037 | |||||
| Chlorine | Cl | 0.2 | 0.024 | |||||
| Magnesium | Mg | 0.1 | 0.015 | |||||
| All others | < 0.1 | < 0.3 |
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.[1]
Some elements (silicon, boron, nickel, vanadium) are probably needed by mammals also, but in far smaller doses. Bromine is used by some (though not all) bacteria, fungi, diatoms, and seaweeds, and opportunistically in eosinophils in humans. One study has indicated bromine to be necessary to collagen IV synthesis in humans.[2] Fluorine is used by a number of plants to manufacture toxins but in humans its only known function is as a local topical hardening agent in tooth enamel.[3]
See main article: article and mineral (nutrient). The average 70kg (150lb) adult human body contains approximately atoms and contains at least detectable traces of 60 chemical elements.[4] About 29 of these elements are thought to play an active positive role in life and health in humans.[5]
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.[6] 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.[7] 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,[8] 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 US National Research Council as beneficial to human health and possibly or probably essential.[9]
| Atomic number | Element | data-sort-type="number" | Fraction of mass [10] [11] [12] [13] [14] [15] ! | data-sort-type="number" | Mass (kg)[16] ! | data-sort-type="number" | Atomic percent! | Essential in humans[17] | Negative effects of excess | Group | |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 8 | data-sort-value="0.65" | 0.65 | 45 | 24 | Yes (e.g. water, electron acceptor)[18] | 16 | |||||
| 6 | data-sort-value="0.18" | 0.18 | 13 | 12 | Yes (organic compounds) | 14 | |||||
| 1 | data-sort-value="0.10" | 0.10 | 7 | 62 | Yes (e.g. water) | 1 | |||||
| 7 | data-sort-value="0.03" | 0.02–0.03 | 1.8 | 1.1 | Yes (e.g. DNA and amino acids) | 15 | |||||
| 20 | data-sort-value="0.014" | 0.011–0.015 | 1.0 | 0.22 | Yes[19] [20] (e.g. Calmodulin and Hydroxylapatite in bones) | 2 | |||||
| 15 | data-sort-value="0.011" | 5– [21] | 0.78 | 0.22 | Yes (e.g. DNA, Phospholipids and Phosphorylation) | 15 | |||||
| 19 | data-sort-value="0.0025" | 1.5–[22] | 0.14 | 0.033 | Yes (e.g. Na+/K+-ATPase) | 1 | |||||
| 16 | data-sort-value="0.0025" | 0.14 | 0.038 | Yes (e.g. Cysteine, Methionine, Biotin, Thiamine) | 16 | ||||||
| 11 | data-sort-value="0.0015" | 0.10 | 0.037 | Yes (e.g. Na+/K+-ATPase) | 1 | ||||||
| 17 | data-sort-value="0.0015" | 0.095 | 0.024 | Yes (e.g. Cl-transporting ATPase) | 17 | ||||||
| 12 | data-sort-value="0.0005" | 0.019 | 0.0070 | Yes (e.g. binding to ATP and other nucleotides) | 2 | ||||||
| 26 | Iron | data-sort-value="0.00006" | data-sort-value=".0042" | 0.0042 | 0.00067 | Yes (e.g. Hemoglobin, Cytochromes) | 8 | ||||
| 9 | data-sort-value="0.000037" | 0.0026 | 0.0012 | Yes (AUS, NZ),[23] No (US, EU),[24] [25] Maybe (WHO)[26] | Fluorine: Highly toxicFluoride: Toxic in high amounts | 17 | |||||
| 30 | data-sort-value="0.000032" | 0.0023 | 0.00031 | Yes (e.g. Zinc finger proteins) | 12 | ||||||
| 14 | data-sort-value="0.00002" | 0.0010 | 0.0058 | Probably[27] | 14 | ||||||
| 31 | data-sort-value="0.00002" | 0.0007 | 0.00093 | No | Gallium halide poisoning[28] | 13 | |||||
| 37 | data-sort-value="0.0000046" | 0.00068 | 0.000033 | No | Potassium replacement | 1 | |||||
| 38 | data-sort-value="0.0000046" | 0.00032 | 0.000033 | No | Calcium replacement | 2 | |||||
| 35 | data-sort-value="0.0000029" | 0.00026 | 0.000030 | Maybe[29] | 17 | ||||||
| 82 | data-sort-value="0.0000017" | 0.00012 | 0.0000045 | No | 14 | ||||||
| 29 | data-sort-value="0.000001" | 0.000072 | 0.0000104 | Yes (e.g. copper proteins) | 11 | ||||||
| 13 | data-sort-value="0.00000087" | 0.000060 | 0.000015 | No | 13 | ||||||
| 48 | data-sort-value="0.00000072" | 0.000050 | 0.0000045 | No | 12 | ||||||
| 58 | data-sort-value="0.00000057" | 0.000040 | No | ||||||||
| 56 | data-sort-value="0.00000031" | 0.000022 | 0.0000012 | No | toxic in higher amounts | 2 | |||||
| 50 | data-sort-value="0.00000024" | 0.000020 | data-sort-value="0.00000060" | Maybe[30] | 14 | ||||||
| 53 | data-sort-value="0.00000016" | 0.000020 | data-sort-value="0.00000075" | Yes (e.g. thyroxine, triiodothyronine) | 17 | ||||||
| 22 | data-sort-value="0.00000013" | 0.000020 | No | 4 | |||||||
| 5 | data-sort-value="0.00000069" | 0.000018 | 0.0000030 | Probably[31] | 13 | ||||||
| 34 | data-sort-value="0.00000019" | 0.000015 | data-sort-value="0.000000045" | Yes (e.g. selenocysteine) | 16 | ||||||
| 28 | data-sort-value="0.00000014" | 0.000015 | 0.0000015 | 10 | |||||||
| 24 | data-sort-value="0.000000024" | 0.000014 | data-sort-value="0.000000089" | 6 | |||||||
| 25 | data-sort-value="0.00000017" | 0.000012 | 0.0000015 | Yes (e.g. Mn-SOD) | 7 | ||||||
| 33 | data-sort-value="0.00000026" | 0.000007 | data-sort-value="0.000000089" | 15 | |||||||
| 3 | data-sort-value="0.000000031" | 0.000007 | 0.0000015 | Possibly (intercorrelated with the functions of several enzymes, hormones and vitamins) | 1 | ||||||
| 80 | data-sort-value="0.00000019" | 0.000006 | data-sort-value="0.000000089" | No | 12 | ||||||
| 55 | data-sort-value="0.000000021" | 0.000006 | data-sort-value="0.00000010" | No | 1 | ||||||
| 42 | data-sort-value="0.00000013" | 0.000005 | data-sort-value="0.000000045" | Yes (e.g. the molybdenum oxotransferases, Xanthine oxidase and Sulfite oxidase) | 6 | ||||||
| 32 | data-sort-value="0.00000005" | No | 14 | ||||||||
| 27 | data-sort-value="0.000000021" | 0.000003 | data-sort-value="0.00000030" | Yes (e.g. Cobalamin/Vitamin B12)[32] [33] | 9 | ||||||
| 44 | data-sort-value="0.000000022" | 0.000007 | No [34] | 8 | |||||||
| 51 | data-sort-value="0.00000011" | 0.000002 | toxic | 15 | |||||||
| 47 | data-sort-value="0.00000001" | 0.000002 | No | 11 | |||||||
| 41 | data-sort-value="0.0000016" | 0.0000015 | No | 5 | |||||||
| 40 | data-sort-value="0.000006" | 0.000001 | data-sort-value="0.00000030" | No | 4 | ||||||
| 57 | data-sort-value="0.00000137" | data-sort-value="0.0000008" | No | ||||||||
| 52 | data-sort-value="0.00000012" | data-sort-value="0.0000007" | No | 16 | |||||||
| 39 | data-sort-value="0.0000006" | No | 3 | ||||||||
| 83 | data-sort-value="0.0000005" | No | 15 | ||||||||
| 81 | data-sort-value="0.0000005" | No | highly toxic | 13 | |||||||
| 49 | data-sort-value="0.0000004" | No | 13 | ||||||||
| 79 | data-sort-value="0.000000003" | data-sort-value="0.0000002" | data-sort-value="0.00000030" | No | uncoated nanoparticles possibly genotoxic[35] [36] [37] | 11 | |||||
| 21 | data-sort-value="0.0000002" | No | 3 | ||||||||
| 73 | data-sort-value="0.0000002" | No | 5 | ||||||||
| 23 | data-sort-value="0.00000026" | data-sort-value="0.000020" | 0.000020 | data-sort-value="0.000000012" | Possibly (suggested osteo-metabolism (bone) growth factor) | 5 | |||||
| 90 | data-sort-value="0.0000001" | No | toxic, radioactive | ||||||||
| 92 | data-sort-value="0.0000001" | data-sort-value="0.0000000030" | No | toxic, radioactive | |||||||
| 62 | data-sort-value="0.000000050" | No | |||||||||
| 74 | data-sort-value="0.000000020" | No | 6 | ||||||||
| 4 | data-sort-value="0.000000036" | data-sort-value="0.000000045" | No | toxic in higher amounts | 2 | ||||||
| 88 | data-sort-value="0.00000000000003" | data-sort-value="0.00000000000000001" | No | toxic, radioactive | 2 | ||||||
| 2 | data-sort-value="0.00000000000000000002039" | data-sort-value="0.000000000000024" | data-sort-value="0.00000000000000001" | No | noble gas | 18 | |||||
| 10 | data-sort-value="0.000000000000000000000085" | data-sort-value="0.00000000000001" | data-sort-value="0.00000000000000001" | No | noble gas | 18 | |||||
| 18 | data-sort-value="0.0000000000000000000000425" | data-sort-value="0.000000000000005" | data-sort-value="0.00000000000000001" | No | noble gas | 18 | |||||
| 36 | data-sort-value="0.00000000000000000000002125" | data-sort-value="0.0000000000000025" | data-sort-value="0.00000000000000001" | No | noble gas | 18 |
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.[38] Transferrins can bind aluminium.[39]
The composition of the human body can be classified as follows:
The estimated contents of a typical 20-micrometre human cell is as follows:[40]
| Compound type | Percent of mass | Mol. weight (daltons) | Compound | Percent of molecules | |
|---|---|---|---|---|---|
| 65 | 18 | 98.73 | |||
| Other inorganics | 1.5 | N/A | 0.74 | ||
| Lipids | 12 | N/A | 0.475 | ||
| 0.4 | N/A | 0.044 | |||
| 20 | N/A | 0.011 | |||
| 1.0 | N/A | ||||
| DNA | 0.1 | 46 |
| scope=col | Cell type | scope=col | % mass | scope=col | % 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 | style="text-align:center;" | - |
Body composition can also be expressed in terms of various types of material, such as:
See main article: List of distinct cell types in the adult human body.
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.[41] [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.