Zinc has been used since ancient Egyptian times to enhance wound healing, although the usefulness of this approach is only partially confirmed by the clinical data of today. Zinc is necessary for the functioning of more than 300 different enzymes and plays a vital role in an enormous number of biological processes. Zinc is a cofactor for the antioxidant enzyme superoxide dismutase (SOD) and is in a number of enzymatic reactions involved in carbohydrate and protein metabolism. 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 thyroid hormones thyroxine to triiodothyronine. Based on available scientific evidence, zinc may be effective in the treatment of (childhood) malnutrition, acne vulgaris, peptic ulcers, leg ulcers, infertility, Wilson's disease, herpes, and taste or smell disorders. Zinc has also gained popularity for its use in the prevention of the common cold. The role for zinc is controversial in some cases, as the results of published studies provide either contradictory information and/or the methodological quality of the studies does not allow for a confident conclusion regarding the role of zinc in those diseases.
Selenium is a trace mineral found in soil, water, and some foods. It is an essential element in several metabolic pathways. Selenium deficiency can occur in areas where the soil content of selenium is low and it may affect thyroid function and cause conditions such as Keshan disease. Selenium deficiency is also commonly seen in patients on total parenteral nutrition (TPN) as their sole source of nutrition. Gastrointestinal disorders may decrease the absorption of selenium resulting in depletion or deficiency. Selenium may be destroyed when foods are refined or processed. Specific dietary sources of selenium include brewer's yeast, wheat germ, butter, garlic, grains, sunflower seeds, Brazil nuts, walnuts, raisins, liver, kidney, shellfish (lobster, oyster, shrimp, scallops), and fresh-water and salt-water fish (red snapper, salmon, swordfish, tuna, mackerel, halibut, flounder, herring, smelts). Selenium is also found in alfalfa, burdock root, catnip, fennel seed, ginseng, raspberry leaf, radish, horseradish, onion, chives, medicinal mushrooms (reishi, shiitake), and yarrow. The role of selenium in cancer prevention has been the subject of recent study and debate. Initial evidence from the Nutritional Prevention of Cancer (NPC) trial suggests that selenium supplementation reduces the risk of prostate cancer among men with normal baseline PSA (prostate specific antigen) levels and low selenium blood levels. However, in this study, selenium did not reduce the risk of lung, colorectal, or basal cell carcinoma of the skin and actually increased the risk of squamous cell skin carcinoma. The ongoing Selenium and Vitamin E Cancer Prevention Trial (SELECT) aims to definitively address the role of selenium in prostate cancer prevention.