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

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

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 Intern 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 97:1338, 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]