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 structure e.g., water, protein, fats, hydroxyapatite, 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

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, & 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 by some 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. 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.

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 other element.
The elements listed below as "Essential in humans" are those listed by the US 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 US 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	45	26	Yes	Reactive oxygen species	16
6	Carbon	0.18	13	9.5	Yes		14
1	Hydrogen	0.10	7	63	Yes	Acidosis	1
7	Nitrogen	0.02–0.03	1.8	1.1	Yes	Nitrogen narcosis	15
20	Calcium	0.011–0.015	1.0	0.21	Yes	Hypercalcaemia	2
15	Phosphorus	5–	0.78	0.12	Yes	Hyperphosphatemia	15
19	Potassium	1.5–	0.14	0.029	Yes	Hyperkalemia	1
16	Sulfur		0.14	0.049	Yes	Sulfhemoglobinemia	16
11	Sodium		0.10	0.041	Yes	Hypernatremia	1
17	Chlorine		0.095	0.027	Yes	Hyperchloremia	17
12	Magnesium		0.019	< 0.01	Yes	Hypermagnesemia	2
26	Iron*		0.0042	< 0.01	Yes	Iron overload	8
9	Fluorine		0.0026	< 0.01	Yes, No, Maybe	Fluorine: Highly toxic Fluoride: Toxic in high amounts	17
30	Zinc		0.0023	< 0.01	Yes	Zinc toxicity	12
14	Silicon		0.0010	< 0.01	Probably		14
31	Gallium		0.0007	< 0.01	No	Gallium halide poisoning	13
37	Rubidium		0.00068	< 0.01	No		1
38	Strontium		0.00032	< 0.001	No	Calcium replacement	2
35	Bromine		0.00026	< 0.001	Maybe	Bromism	17
82	Lead		0.00012	< 0.001	No	Lead poisoning	14
29	Copper		0.000072	< 0.001	Yes	Copper toxicity	11
13	Aluminium		0.000060	< 0.001	No	Aluminium poisoning	13
48	Cadmium		0.000050	< 0.001	No	Cadmium poisoning	12
58	Cerium		0.000040	< 0.001	No
56	Barium		0.000022	< 0.001	No	toxic in higher amounts	2
50	Tin		0.000020	< 0.001	Maybe		14
53	Iodine		0.000020	< 0.001	Yes	Iodine-induced hyperthyroidism	17
22	Titanium		0.000020	< 0.001	No		4
5	Boron		0.000018	< 0.001	Probably		13
34	Selenium		0.000015	< 0.001	Yes	Selenium toxicity	16
28	Nickel		0.000015	< 0.0001	Maybe	Nickel Toxicity	10
24	Chromium		0.000014	< 0.0001	Maybe		6
25	Manganese		0.000012	< 0.0001	Yes	Manganism	7
33	Arsenic		0.000007	< 0.0001	Maybe	Arsenic poisoning	15
3	Lithium		0.000007	< 0.0001	Possibly	Lithium toxicity	1
80	Mercury		0.000006	< 0.0001	No	Mercury poisoning	12
55	Caesium		0.000006	< 0.0001	No		1
42	Molybdenum		0.000005	< 0.0001	Yes		6
32	Germanium			< 0.0001	No		14
27	Cobalt		0.000003	< 0.0001	Yes	Cobalt poisoning	9
44	Ruthenium		0.000007	< 0.0001	No		8
51	Antimony		0.000002	< 0.0001	No	toxic	15
47	Silver		0.000002	< 0.0001	No		11
41	Niobium		0.0000015	< 0.0001	No		5
40	Zirconium		0.000001	< 0.0001	No		4
57	Lanthanum			< 0.0001	No
52	Tellurium			< 0.0001	No		16
39	Yttrium			< 0.0001	No		3
83	Bismuth			< 0.0001	No		15
81	Thallium			< 0.0001	No	highly toxic	13
49	Indium			< 0.0001	No		13
79	Gold			< 0.0001	No	uncoated nanoparticles possibly genotoxic	11
21	Scandium			< 0.0001	No		3
73	Tantalum			< 0.0001	No		5
23	Vanadium		0.000020	< 0.0001	Possibly		5
90	Thorium			< 0.0001	No	toxic, radioactive
92	Uranium			< 0.0001	No	toxic, radioactive
62	Samarium			< 0.0001	No
74	Tungsten			< 0.0001	No		6
4	Beryllium			< 0.0001	No	toxic in higher amounts	2
88	Radium			< 0.0001	No	toxic, radioactive	2
2	Helium			< 0.0001	No	noble gas	18
10	Neon			< 0.0001	No	noble gas	18
18	Argon			< 0.0001	No	noble gas	18
36	Krypton			< 0.0001	No	noble gas	18

*Iron = ~3 g in males, ~2.3 g in females
Of the 94 naturally occurring chemical elements, 76 are listed in the table above. Of the remaining 18, 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.

Composition

The composition of the human body can be classified as follows:

Water
Proteins
Fats
Hydroxyapatite in bones
Carbohydrates such as glycogen and glucose
DNA and RNA
Inorganic ions such as sodium, potassium, chloride, bicarbonate, phosphate
Gases mainly being oxygen, carbon dioxide
Many cofactors.

The estimated contents of a typical 20-micrometre human cell is as follows:

Compound type	Percent of mass	Mol. weight	Compound	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

Body composition 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, there are roughly as many microbial as human cells in the human body by number.
. Some of these symbionts are necessary for our health. Those that neither help nor harm humans are called commensal organisms.