Essential elements

In the Human Body

Element	Percent by Mass*
Oxygen	65
Carbon	18
Hydrogen	10
Nitrogen	3
Calcium	1.6
Phosphorus	1.2
Potassium	0.2
Sulfur	0.2
Chlorine	0.2
Sodium	0.1
Magnesium	0.05
Iron	Less than 0.05
Cobalt	Less than 0.05
Copper	Less than 0.05
Zinc	Less than 0.05
Iodine	Less than 0.05
Selenium	Less than 0.01
Flourine	Less than 0.01

Percent by mass given in grams present in a 100 gram sample*

Elements of special interest are the trace elements, including iron (Fe), copper (Cu), zinc (Zn), iodine (I), and cobalt (Co). Together these elements make up about 0.1 percent of the body's mass. They are necessary for biological functions such as defense against disease, growth, and transport of oxygen for metabolism. The human body has a delicate balance of these elements and too much or too little over an extended period of time can lead to serious illness, retardation, or even death.