Chapter 071. Vitamin and Trace Mineral Deficiency and Excess (Part 13) docx

Chapter 071. Vitamin and Trace Mineral Deficiency and Excess (Part 13) Selenium Selenium, in the form of selenocysteine, is a component of the enzyme glutathione peroxidase, which serves to protect proteins, cell membranes, lipids, and nucleic acids from oxidant molecules. As such, selenium is being actively studied as a chemopreventive agent against certain cancers, such as prostate. Selenocysteine is also found in the deiodinase enzymes, which mediate the deiodination of thyroxine to triiodothyronine (Chap. 335). Rich dietary sources of selenium include seafood, muscle meat, and cereals, although the selenium content of cereal is determined by the soil concentration. Countries with low soil concentrations include parts of Scandinavia, China, and New Zealand. Keshan disease is an endemic cardiomyopathy found in children and young women residing in regions of China where dietary intake of selenium is low (<20 µg/d). Concomitant deficiencies of iodine and selenium may worsen the clinical manifestations of cretinism. Chronic ingestion of high amounts of selenium leads to selenosis characterized by hair and nail brittleness and loss, garlic breath odor, skin rash, myopathy, irritability, and other abnormalities of the nervous system. Chromium Chromium potentiates the action of insulin in patients with impaired glucose tolerance, presumably by increasing insulin receptor–mediated signaling, although its usefulness in treating type II diabetes is uncertain. In addition, improvement in blood lipid profiles has been reported in some patients. The usefulness of chromium supplements in muscle building is not substantiated. Rich food sources of chromium include yeast, meat, and grain products. Chromium in the trivalent state is found in supplements and is largely nontoxic; however, chromium-6 is a product of stainless steel welding and is a known pulmonary carcinogen, as well as a cause of liver, kidney, and CNS damage. Magnesium See Chap. 346. Fluoride, Manganese, and Ultratrace Elements An essential function for fluoride in humans has not been described, although it is useful for the maintenance of structure in teeth and bone. Adult fluorosis results in mottled and pitted defects in tooth enamel as well as brittle bone (skeletal fluorosis). Manganese and molybdenum deficiencies have been reported in patients with rare genetic abnormalities and in a few patients receiving prolonged total parenteral nutrition. Several manganese-specific enzymes have been identified (e.g., manganese superoxide dismutase). Deficiencies of manganese have been reported to result in bone demineralization, poor growth, ataxia, disturbances in carbohydrate and lipid metabolism, and convulsions. Ultratrace elements are defined as those needed in amounts <1 mg/d. Essentiality has not been established for most ultratrace elements, although selenium, chromium, and iodine are clearly essential (Chap. 335). Molybdenum is necessary for the activity of sulfite and xanthine oxidase, and molybdenum deficiency may result in skeletal and brain lesions. Further Readings Bonaa KH et al: Homocysteine lowering and cardiovascular events after acute myocardial infarction. N Engl J Med 354:1578, 2006 [PMID: 16531614] Day E et al: Thiamine for Wernicke- Korsakoff Syndrome in people at risk from alcohol abuse. Cochrane Database Syst Rev CD004033, 2004 Lichtenstein AH, Russell RM: Essential nutrients in a healthy diet: Food or supplements? JAMA 294:1, 2005 Miller ER et al: Meta-analysis: High- dosage vitamin E supplementation may increase all-cause mortality. Ann Inte rn Med 142:37, 2005 [PMID: 15537682] Morris MC et al: Dietary folate and vitamin B12 intake and cognitive decline among community- dwelling older persons. Arch Neurol 62:641, 2005 [PMID: 15824266] Murphy SP et al: Multivitamin-multimineral supplements’ effect on total nutrient intake. Am J Clin Nutr 85(1):280S, 2007 Penniston KL, Tanumihardjo: The acute and chronic toxic effects of vitamin A. Am J Clin Nutr 83:191, 2006 [PMID: 16469975] Prentice RL: Clinical trials and observational studies to assess the chronic disease benefits and risks of multivitamin- multimineral supplements. Am J Clin Nutr 85(1):308S, 2007 Touvier M et al: Dual association of beta-carotene with risk of tobacco- related cancers in a cohort of French women. J Natl Cancer Inst 97:1 338, 2005 [PMID: 16174855] Vermeer C et al: Beyond deficiency: Potential benefits of increased intakes of vitamin K for bone and vascular health. Eur J Nutr 43:325, 2004 [PMID: 15309455] . Chapter 071. Vitamin and Trace Mineral Deficiency and Excess (Part 13) Selenium Selenium, in the form of selenocysteine, is. ultratrace elements, although selenium, chromium, and iodine are clearly essential (Chap. 335). Molybdenum is necessary for the activity of sulfite and xanthine oxidase, and molybdenum deficiency. have been reported to result in bone demineralization, poor growth, ataxia, disturbances in carbohydrate and lipid metabolism, and convulsions. Ultratrace elements are defined as those needed