The mineral selenium in conjunction with vitamin E is essential in this function. Vitamin A is protective of epithelial tissue and is especially important in smokers who tend to be deficient in this vitamin. Antioxidants may also play a role in preventing heart disease. Magnesium is an essential element in human metabolism and functions in the activities of muscles and nerves, protein synthesis, and many other reactions. Magnesium deficiency may occur in alcoholism, diabetes mellitus, pancreatitis, and renal diseases.
Prolonged deficiency can cause changes in heart and skeletal muscle.
Excessive retention of magnesium can occur in renal disease and results in muscle weakness and hypertension. The one important function of iodine is associated with the synthesis of thyroxine and the function of the thyroid gland. Persons living in coastal regions usually receive an adequate supply of iodine because of the high content in seafood. Elemental iodine is highly poisonous, and its only use in medicine is as an antiseptic.