Zinc is an essential mineral that is found in almost every cell. Zinc supports a healthy immune system, is needed for wound healing, helps maintain your sense of taste and smell, and is needed for DNA synthesis. Zinc also supports normal growth and development during pregnancy, childhood, and adolescence. (Nutr Rev 1998; 56:27).
Zinc deficiency most often occurs when zinc intake is inadequate or poorly absorbed, when there are increased losses of zinc from the body, or when the body's requirement for zinc increases. Signs of zinc deficiency include growth retardation, hair loss, diarrhea, eye and skin lesions, and loss of appetite.
The immune system is adversely affected by even moderate degrees of zinc deficiency. Severe zinc deficiency depresses immune function. Zinc is required for the development and activation of T-lymphocytes, a kind of white blood cell that helps fight infection. When zinc supplements are given to individuals with low zinc levels, the numbers of T-cell lymphocytes circulating in the blood increase and the ability of lymphocytes to fight infection improves. (Am J Clin Nutr.1998; 68:447).
The effect of zinc treatments on the severity or duration of cold symptoms is controversial, and additional research is needed to determine whether zinc compounds have any effect on the common cold. Zinc toxicity can cause altered iron function, reduced immune function, and reduced levels of HDL ("good") cholesterol.