Zinc (Zn) is contained mainly in bones, teeth, hair, skin, liver, muscle, leukocytes, and testes. Zinc is a component of several hundred enzymes, including many nicotinamide adenine dinucleotide (NADH) dehydrogenases, RNA and DNA polymerases, and DNA transcription factors as well as alkaline phosphatase, superoxide dismutase, and carbonic anhydrase. Zinc plays a vital role in an enormous number of biological processes. Its immune-enhancing activities include regulation of T lymphocytes, CD4, natural killer cells, and interleukin II. In addition, zinc has been claimed to possess antiviral activity. It has been shown to play a role in wound healing, especially following burns or surgical incisions. Zinc is necessary for the maturation of sperm and normal fetal development. It is involved in sensory perception (taste, smell, and vision) and controls the release of stored vitamin A from the liver. Within the endocrine system, zinc has been shown to regulate insulin activity and promote the conversion of thyroid hormone thyroxine to triiodothyronine. Zinc DEFICIENCY can develop in the following: hepatic insufficiency, patients taking diuretics, with diabetes mellitus, sickle cell disease, chronic renal failure, or malabsorption. It can also develop in patients with stressful conditions (eg, sepsis, burns, or head injury). Zinc deficiency in children causes impaired growth and impaired taste (hypogeusia). Other symptoms and signs in children include delayed sexual maturation and hypogonadism. In adults, symptoms include hypogonadism, alopecia, impaired immunity, anorexia, dermatitis, night blindness, anemia, lethargy, and impaired wound healing. Zinc TOXICITY can cause anorexia, vomiting, and diarrhea.