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, hydroxylapatite, carbohydrates 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 are not human cells, but bacteria residing in the normal human gastrointestinal tract.

Elements

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 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. All of the mass of the trace elements put together do not add up to the body mass of magnesium, the least common of the 11 non-trace elements.

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, while many others are thought to be active toxins, depending on amount. In humans, arsenic is toxic, and its levels in foods and dietary supplements are closely monitored to reduce or eliminate its intake.
Some elements are probably needed by mammals also, but in far smaller doses. Bromine is used abundantly by some lower organisms, and opportunistically in eosinophils in humans. One study has indicated bromine to be necessary to collagen IV synthesis in humans. Fluorine is used by a number of plants to manufacture toxins but in humans only functions as a local hardening agent in tooth enamel, and not in an essential biological role.

Elemental composition list

The average adult human body contains approximately atoms and contains at least detectable traces of 60 chemical elements. About 29 of these elements are thought to play an active positive role in life and health in humans.
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 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. 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 Food and Drug Administration as essential nutrients, as well as six additional elements: oxygen, carbon, hydrogen, and nitrogen, sulfur and cobalt. Elements listed as "Possibly" or "Probably" essential are those cited by the National Research Council as beneficial to human health and possibly or probably essential.

Atomic number	Element	Fraction of mass	Mass	Atomic percent	Essential in humans	Negative effects of excess	Group
8	Oxygen	0.65	43	24	Yes	Reactive oxygen species	16
6	Carbon	0.18	16	12	Yes		14
1	Hydrogen	0.10	7	62	Yes		1
7	Nitrogen	0.03	1.8	1.1	Yes		15
20	Calcium	0.014	1.0	0.22	Yes		2
15	Phosphorus	0.011	0.78	0.22	Yes	Hyperphosphatemia	15
19	Potassium		0.14	0.033	Yes		1
16	Sulfur		0.14	0.038	Yes		16
11	Sodium		0.10	0.037	Yes		1
17	Chlorine		0.095	0.024	Yes		17
12	Magnesium		0.019	0.0070	Yes		2
26	Iron*		0.0042	0.00067	Yes		8
9	Fluorine		0.0026	0.0012	Yes, No, Maybe	toxic in high amounts	17
30	Zinc		0.0023	0.00031	Yes		12
14	Silicon		0.0010	0.0058	Possibly		14
31	Gallium		?	0.0007	No		13
37	Rubidium		0.00068	0.000033	No		1
38	Strontium		0.00032	0.000033	——		2
35	Bromine		0.00026	0.000030	——		17
82	Lead		0.00012	0.0000045	No	toxic	14
29	Copper		0.000072	0.0000104	Yes		11
13	Aluminium		0.000060	0.000015	No		13
48	Cadmium		0.000050	0.0000045	No	toxic	12
58	Cerium		0.000040		No
56	Barium		0.000022	0.0000012	No	toxic in higher amounts	2
50	Tin		0.000020		No		14
53	Iodine		0.000020		Yes		17
22	Titanium		0.000020		No		4
5	Boron		0.000018	0.0000030	Probably		13
34	Selenium		0.000015		Yes	toxic in higher amounts	16
28	Nickel		0.000015	0.0000015	Probably	toxic in higher amounts	10
24	Chromium		0.000014		Yes		6
25	Manganese		0.000012	0.0000015	Yes		7
33	Arsenic		0.000007		No	toxic	15
3	Lithium		0.000007	0.0000015	Yes	toxic in higher amounts	1
80	Mercury		0.000006		No	toxic	12
55	Caesium		0.000006		No		1
42	Molybdenum		0.000005		Yes		6
32	Germanium				No		14
27	Cobalt		0.000003		Yes		9
51	Antimony		0.000002		No	toxic	15
47	Silver		0.000002		No		11
41	Niobium		0.0000015		No		5
40	Zirconium		0.000001		No		4
57	Lanthanum				No
52	Tellurium				No		16
39	Yttrium				No		3
83	Bismuth				No		15
81	Thallium				No	highly toxic	13
49	Indium				No		13
79	Gold				No	uncoated nanoparticles possibly genotoxic	11
21	Scandium				No		3
73	Tantalum				No		5
23	Vanadium				Possibly		5
90	Thorium				No	toxic, radioactive
92	Uranium				No	toxic, radioactive
62	Samarium				No
74	Tungsten				No		6
4	Beryllium				No	toxic in higher amounts	2
88	Radium				No	toxic, radioactive	2
71	Lutetium				Possibly	toxic in higher amounts	4

*Iron = ~3 g in men, ~2.3 g in women
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, 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. Transferrins can bind aluminium.

Periodic table

Molecules

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

Water
Proteins – including those of hair, connective tissue, etc.
Fats
Hydroxyapatite in bones
Carbohydrates such as glycogen and glucose
DNA
Dissolved inorganic ions such as sodium, potassium, chloride, bicarbonate, phosphate
Gases such as oxygen, carbon dioxide, nitrogen oxide, hydrogen, carbon monoxide, acetaldehyde, formaldehyde, methanethiol. These may be dissolved or present in the gases in the lungs or intestines. Ethane and pentane are produced by oxygen free radicals.
Many other small molecules, such as amino acids, fatty acids, nucleobases, nucleosides, nucleotides, vitamins, cofactors.
Free radicals such as superoxide, hydroxyl, and hydroperoxyl.

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:

Molecule	Percent of Mass	Mol.Weight	Molecules	Percent of Molecules
Water	65	18		98.73
Other Inorganics	1.5	N/A		0.74
Lipids	12	N/A		0.475
Other Organics	0.4	N/A		0.044
Protein	20	N/A		0.011
RNA	1.0	N/A
DNA	0.1		46*

Tissues

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

Muscle
Fat
Bone and teeth
Nervous tissue
Hormones
Connective tissue
Body fluids
Contents of digestive tract, including intestinal gas
Air in lungs
Epithelium
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 a human body are microbes, by number. Some of these symbionts are necessary for our health. Those that neither help nor harm humans are called commensal organisms.

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