Chemical Composition of the Human Body

Human Body Composition as Elements and Compounds

Most of the human body consists of water, which is made from hydrogen and oxygen.
Most of the human body consists of water, which is made from hydrogen and oxygen. Youst / Getty Images

This is the chemical composition of the average adult human body in terms of elements and also compounds.

Major Classes of Compounds in the Human Body

  • Water: Water is the most abundant chemical compound in living human cells, accounting for 65-90% of each cell. It's also present between cells. For example, blood and cerebrospinal fluid are mostly water.
  • Fat: The percentage of fat varies from person to person, but even an obese person has more water than fat.
  • Protein: In a lean male, the percent of fat and water is comparable. It's about 16% by mass. Muscles, including the heart, contain a lot of muscle. Hair and fingernails are protein. Skin contains a large amount of protein, too.
  • Minerals: Mineral account for about 6% of the body. They include salts and metals. Common minerals include sodium, chlorine, calcium, potassium, and iron.
  • Carbohydrates: Although humans use the sugar glucose as an energy source, there isn't that much of it free in the bloodstream at any given time. Carbohydrates only account for about 1% of body mass.

Elements in the Human Body

Six elements account for 99% of the mass of the human body. The acronym CHNOPS may be used to help remember the six key chemical elements that are used in biological molecules. C is carbon, H is hydrogen, N is nitrogen, O is oxygen, P is phosphorus, and S is sulfur. While it's a good way to remember the identities of the elements, it doesn't reflect their abundance.

Oxygen is the most abundant element in the human body accounting for approximately 65% of a person's mass. Each water molecule consists of two hydrogen atoms bonded to one oxygen atom, but the mass of each oxygen atom is much higher than the combined mass of the hydrogen. In addition to being a component of water, oxygen is essential for cellular respiration.

All organic compounds contain carbon, which is why carbon is the second most abundant element in the body, accounting for about 18% of body mass. Carbon is found in proteins, carbohydrates, lipids, and nucleic acids. It's also found in carbon dioxide.

Hydrogen atoms are the most numerous type of atom in a human, but because they are so light, they only make up around 10% of the mass. Hydrogen is in water, plus it's an important electron carrier.

Nitrogen is about 3.3% of body mass. It's found in proteins and nucleic acids.

Calcium accounts for 1.5% of body mass. It's used to build bones and teeth, plus it's important for muscle contraction.

Phosphorus is about 1% of body mass. This element is found in nucleic acids. Breaking bonds connecting phosphate molecules is a major component of energy transfer.

Potassium is around 0.2-0.4% of the mass of a person. It's used in nerve conduction. Potassium is a key cation or positively-charged ion in the body.

Sulfur is found in some amino acids and proteins. It's about 0.2-0.3% of body mass.

Sodium, like potassium, is a positively-charged ion. It's about 0.1-0.2% of body mass.

Although aluminum and silicon are abundant in the earth's crust, they are found in trace amounts in the human body.

ElementPercent by Mass
Oxygen65
Carbon18
Hydrogen10
Nitrogen3
Calcium1.5
Phosphorus1.2
Potassium0.2
Sulfur0.2
Chlorine0.2
Sodium0.1
Magnesium0.05
Iron, Cobalt, Copper, Zinc, Iodine 

Selenium, Fluorine

 

Reference: Chang, Raymond (2007). Chemistry, Ninth Edition. McGraw-Hill. pp. 52.