An essential trace element, zinc is found in every cell of the body and performs numerous useful functions. It is a component of some 200 enzymes and is involved in more enzymatic reactions than any other mineral. It is a constituent of insulin, growth hormones and sex hormones, and is richly contained in human sperm. It takes part in carbohydrate metabolism, the breakdown of alcohol and the synthesis of nucleic acids. Together with vitamins A, B6 and B12, zinc is necessary for proper growth. It also aids the excretion of toxic cadmium found in cigarette smoke (which causes hypertension), and neutralizes the bad effects of excess copper (a cause of arthritis). Zinc is crucial to the maturation of the sex glands and for their function, particularly the prostate. It prevents enlargement of the prostate, which can block urine flow and is a source of distress for many men over 45. Together with vitamin B6, zinc inhibits histamine production and is therefore helpful in treating allergies. It soothes nerves and depression and is used in the treatment of Alzheimer's disease and some types of schizophrenia. Zinc can also speed up the healing of wounds and is used to care ulcers resulting from cortisone treatment. Due to its presence in insulin, zinc increases the insulin effect and is therefore helpful in the treatment of diabetes. It has also been found to boost natural immunity against disease and is well-known for its ability to promote skin health and alleviate psoriasis. For this reason, it is sometimes used as an ingredient in skin creams. The symptoms of zinc deficiency are many and varied. They include swollen prostate, sterility and impotence and delayed sexual maturation in children, stunted growth, menstrual irregularities, susceptibility to infections and poor wound healing, joint pains, atherosclerosis and poor circulation, slow learning and mental retardation, loss of sense of taste and smell, allergies, acne, stretch marks in pregnant women, white spots in the nails, offensive perspiration, and susceptibility to diabetes. Zinc is depleted by alcohol and smoking, and profuse sweating can cause a loss of up to 3 mg a day. Among the best natural sources of the mineral are raw oysters, clams, meat, fish, raw wheat germ, brewer's yeast, mushrooms, pumpkin seeds, egg yolks and legumes. The Recommended Daily Allowance is 15 mg for adults and 10 mg for children. Requirements increase during pregnancy or lactation. Zinc supplements in strengths of up to 40 mg are available in health food stores.