The elemental 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. 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. Body composition may also be analyzed in terms
of molecular type apatite, carbohydrates 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 are not human cells, but consist of bacteria residing in the normal human gastrointestinal
tract. Major, minor and trace 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 are necessary to life. 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.
An easy way to remember the six most essential elements in living organisms is CHONPC.
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, while
many others are thought to be active toxics, depending on amount. The possible utility
and toxicity of a few elements at levels normally found in the body 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. Some elements that are clearly used in lower
organisms and plants are probably needed by mammals also, but in far smaller doses. Two
halogens used abundantly by some lower organisms are presently known to be used by mammals
only opportunistically. Elemental composition list The average 70 kg adult human body contains
approximately 7 x 1027 atoms and contains at least detectable traces of 60 chemical
elements. About 25 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. 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.
*Iron=~3 g in men, ~2.3 g in women The elements needed for life are relatively
common in the Earth’s crust, and conversely most of the common elements are necessary
for life. An exception is aluminium, which is the third most common element in the Earth’s
crust, but seems to serve no function in living cells. Rather, it is harmful in large amounts.
Transferrins can bind aluminium. Essential elements on the periodic table
Periodic table highlighting dietary elements Composition by molecule type
The composition can also be expressed in terms of chemicals, such as:
Water Proteins – including those of hair, connective
tissue, etc. Fats
Apatite 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, 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:
*Water: Obviously the amount of water is highly dependent on body composition and amount of
fat. In adults in developed countries it actually 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. DNA: A human cell also contains mitochondrial DNA. Sperm cells contain less
mitochondrial DNA than other cells. A mammalian red blood cell contains no nucleus and thus
no DNA. Materials and tissues
Body composition can also be expressed in terms of various types of material, such as:
Bone and teeth Brain and nerves
Connective tissue Blood – 7% of body weight.
Lymph Contents of digestive tract, including intestinal
Air in lungs 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. See also
Hydrostatic weighing Dietary mineral
Composition of blood List of human blood components
Body composition Abundance of elements in Earth’s crust
Abundance of the chemical elements References