Chromium

Physiological Role
Absorption and Excretion of Cr
Requirements for Cr
Chromium in Foods
Deficiency of Cr
Toxicity of Cr

I.  Physiological Role

1. Other transition elements such as Fe, Zn, Cu and Mo function in enzyme systems, metallo-protein complexes, and related structures
2. No such role for Cr has yet been identified
   1. Is Cr the exception among the transition elements?
   2. Or, do the exceedingly small amounts in which it occurs elude measurement capabilities to date?
3. Cr is biologically active only in the form of glucose tolerance factor (GTF) which consists of the following: Cr (111), nicotinic acid and glutathione (which consists of the amino acids glycine, cysteine, and glutamic acid).
   1. Other forms of Cr must be converted to GTF before exerting biological activity
   2. GTF occurs preformed in certain foods and can be utilized directly by humans and animals
   3. Different individuals have different abilities to synthesize GTF from inorganic Cr, niacin, and amino acids
   4. Different individuals depend on preformed GTF to different degrees
   5. Site of GTF synthesis may be the intestinal flora or a special tissue (possibly the liver)
4. Cr in its biologically active form resembles a hormone
   1. It is released into the blood in response to a physiological stimulus (insulin)
   2. It is transported to the periphery where it facilitates a reaction
   3. In the absence of GTF, the reaction would occur at a much slower rate

II.  Absorption and Excretion of Cr

1. Inorganic Cr is largely unavailable and excreted with the feces (only 0.5% is absorbed)
2. Cr in GTF is well absorbed and retained (up to 25%)
3. Urine is the major excretory route of absorbed Cr (95%).

III.  Requirements for Cr

1. Minimum requirement of absorbable Cr is near 15 ug/day in humans
   1. Dietary Cr requirement is much more difficult to determine than absorbable Cr requirement because of the great difference in biological availability of Cr in different foods
   2. Cr requirement is increased by diabetes, pregnancy, and lactation
   3. A tentative range of 50-200 ug/day of dietary Cr has been suggested by NRC as safe and adequate for healthy adults

IV.  Chromium in Foods (Present Knowledge in Nutrition, 1984; J. Nutr. 126:2441S, 1996)

1. Good sources of Cr (value reported before 1980 are generally inaccurate)
   1. Meat, poultry, fish, dairy products tend to be low
   2. Fruits, vegetables, and grain products are variable in Cr
   3. Beans, other seeds and dark chocolate may contain more Cr than other foods
   4. Yeast
   5. Molasses and unrefined brown sugar
   6. Black pepper is a concentrated source, but is not generally consumed in amounts sufficient to contribute significantly to the diet
2. Acidic foods promote leaching of Cr from stainless steel but it has not be determined whether this is a nutritionally useful Cr source

V.  Deficiency of Cr

1. Occurrence of Cr deficiency
   1. Associated with protein - calorie malnutrition
   2. Marginal Cr deficiency is suspected to exist in USA during pregnancy and old age
2. Signs of Cr deficiency
   1. Unexpected weight loss
   2. Impaired glucose tolerance
   3. Decreased respiratory quotient
   4. Peripheral neuropathy
   5. Pronounced negative nitrogen balance
   6. Low blood and hair Cr levels
   7. Negative Cr balance

VI.  Toxicity of Cr

1. Cr (VI) compounds appear to be more toxic than Cr (III)
2. Acute systemic Cr intoxication is rare but has been produced
   1. Single oral dose of 700 mg/kg BW of Cr (VI) in mature cattle
   2. Single oral dose of 30-40 mg kg BW of Cr (VI) in young calves
   3. Maximum tolerable dietary levels have been set at 3,000 ppm as the oxide and 1,000 ppm as the chloride for domestic animals

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