Page 210 - Academic Press Encyclopedia of Physical Science and Technology 3rd BioChemistry

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Encyclopedia of Physical Science and Technology EN017G-116 August 2, 2001 18:14

518 Vitamins and Coenzymes

TABLE II (Continued)
Nutrient Approximate daily need (mg or g) Major biological function
Phosphorus P 275 700 Present in nucleic acids, proteins, coenzymes
Magnesium as Mg 2+ 75 300 Enzyme activator, often associated with
organic phosphate groups; electrolyte
Zinc as Zn 2+ 5 15 Structural; catalytic component in active
sites of enzymes
Iron Fe 1 1 (men) Active sites of oxidative enzymes,
2 (young women) electron transport proteins
Copper Cu 1.5–3 mg Oxidative enzymes, electron-transferring
proteins
Manganese Mn 2–5 mg Component of enzymes
Iodine I 150 µg Formation of thyroxine, triiodothyronine
Sulfur S Largely supplied as cysteine or methionine
(above)
Selenium Se 50 µg Formation of selenocysteine, component
of active sites of several enzymes and
other proteins
Molybdenum Mo 25 µg Formation of sulfite oxidase and other
molybdoenzymes
Chromium Cr 50 µg Utilization of glucose
Cobalt Co as vitamin B 12 (Table I)
Ultratrace elements, probably needed or beneficial Most functions are uncertain
Boron B 1–10 mg Crosslinking?
Fluorine F 1.5–4 mg Protective component of hydroxyapatite in
teeth, bones
Arsenic As 15 µg
Silicon Si 5–30 µg Crosslinking in connective tissue
Nickel Ni 25–35 µg Uncertain
Vanadium V Component of thyroid peroxidase
Possibly needed Typical dietary intake Functions are unknown
Aluminium Al 2 mg
Bromine Br 2–8mg
Cadmium Cd 0–20 µg (toxic in excess)
Germanium Ge 0.4–1.5 mg (toxic in excess)
Lead Pb 15–100 µg (toxic in excess)
Lithium Li 0.2–0.6 mg
Rubidium Rb 1–5mg
Tin Sn 1–40 mg
a Data are from Shils, M. E., et al., eds. (1999). Modern Nutrition in Health and Disease, 9th ed., Williams & Wilkins, Baltimore. This book can be
consulted for detailed discussions of all of the listed dietary components.
b The need for methionine is decreased if cysteine (or cystine) is present. Likewise, tyrosine decreases the need for phenylalanine. Persons with
phenylketonuria must have tyrosine.

condition in which red blood cells do not mature nor- year. Fortunately, the problem can be alleviated inexpen-
mally and in which dementia develops as a result of sively. A single oral dose of vitamin A provides a store in
the lack of vitamin B 12 in the brain. If treated in time, the liver adequate for 4–6 months. An international effort
a monthly injection of one milligram of the vitamin is to eradicate vitamin A deficiency as a cause of blindness is
curative. in progress. Deficiency also interferes with reproduction.
Adeficit of vitamin A causes night blindness and loss The yellow beta-carotene and some related plant pigments
of proper differentiation of epithelial cells. A dangerous can be converted by the human body into vitamin A. About
symptom is the dry eye condition xerophthalmia, which six micrograms of all-trans beta-carotene yields one mi-
can cause blindness. In fact, thousands of children in de- crogram of the vitamin. In large excess, vitamin A, espe-
veloping countries become blind from this condition each cially in the form of retinoic acid, is toxic. About 3 mg