Chromium
Description
Chromium is an essential trace mineral involved in protein, fat and carbohydrate metabolism. It is the primary component of the Glucose Tolerance Factor (GTF)--the biologically active form of chromium that boosts insulin's action.
Chromium concentration in human plasma is so variable that a reliable average value is difficult to determine. However, it is estimated an adult has less than six milligrams of chromium in his or her body, which tends to accumulate in hair, skin, muscle, and fat. Hair and urine analysis are currently used to estimate chromium levels in humans, however, a reliable means of detection is currently not available.
A study by the U.S. Department of Agriculture found the diets of nine out of 10 Americans tested were deficient in chromium. Factors increasing chromium losses from the body include aerobic exercise, diets high in simple sugars, pregnancy, diabetes, injury, illness and other forms of stress. Tissue chromium levels are also known to decrease steadily with age. People at increased risk of chromium deficiency include athletes, diabetics, child-bearing women and the elderly.
Method of Action
The primary function of biologically active Glucose Tolerance Factor (GTF) chromium is to facilitate insulin action. It does this by binding insulin to cell membranes, serving as a bridge between the insulin molecule and cell membrane receptor sites. At these sites, insulin transports blood sugar (glucose), fatty acids and vital amino acids inside the cell for energy and tissue synthesis.
GTF consists of an organic chromium complex containing the B vitamin niacin and certain amino acids. Chromium by itself has no effect on insulin action.
Aside from its effect on insulin metabolism, chromium also serves as a cofactor of trypsin, and is important in the regulation of various enzymatic activities. In small quantities, chromium has been found to be associated with RNA.
Once chromium is mobilized from body tissue stores for its various uses, approximately 95% is excreted away in the urine. Less than 5% is reabsorbed by the kidneys and returned to storage.
Simple chromium compounds, such as chromium chloride, are poorly absorbed--typically 0.5% to 2%. Biologically active GTF chromium is aborbed about 10% to 25%. Once absorbed, chromium excretion occurs primarily in the urine.
Properties & Uses
Chromium, via its effect on insulin metabolism, is involved in the regulation of blood sugar, blood lipids and body composition. Studies show that chromium supplements can improve hypoglycemia, lower cholesterol, increase beneficial HDL cholesterol, and decrease body weight.
Chromium is effective in reducing glucose intolerance, suffered by many elderly persons. It has also been used to improve the glucose tolerance in some children with kwashiorkor.
Consequence of Deficiency
Chromium deficiencies are inexorably linked to the refining of foods, especially whole grains.
Symptoms of chromium deficiency include decreased glycogen reserves, retarded growth, disturbed amino acid metabolism, and elevated serum cholesterol levels, possibly accompanied by increased aortic lesions.
Chromium deficiencies have been associated with decreased glucose tolerance and with an increased incidence of diabetes, both of which become increasingly common with age.
Chromium deficiency may appear more generally as premature coronary heart disease, impaired growth, or a decreasing ratio of carbon dioxide exhaled per volume of oxygen inhaled.
Toxicity Factors
The toxicity of trivalen chromium (Cr+3), the chemical form occurring in diets and nutritional supplements, is so low that a substantial margin of safety exists between the amounts normally consumed and those considered to have harmful effects.
No adverse effects were found in cats and rats consuming many thousands of times the maximum amount recommended for humans, and no adverse effects of trivalent chromium in humans has been reported in the medical literature.
Accidental ingestion of hexavalent chromium (Cr+6) used in industry has been correlated with liver and kidney damage as well as lung cancer. But since humans cannot convert trivalent chromium into hexavalent chromium, the potential toxicity of hexavalent chromium bears no relevance to the nutritional role of trivalent chromium.
Recommended Dietary Allowance
No U.S. RDA has been established for chromium, however, the National Reasearch Council's Food and Nutrition Board has established an estimated safe an adequate daily dietary intake of chromium for adults at 50 to 200 micrograms.
For over thirty years, Recommended Daily Amounts has existed in the United Kingdom. It has been used to measure the adequacy of an individual's diet. However, in 1991 the Committee on Medical Aspects of Food Policy (COMA) gave forth a whole new set of figures upon the request of the Department of Health's Chief Medical Officer. Reference Nutrient Intake (RNI) is one of these sets collectively known as "Dietary Reference Values." RNI is an amount of a nutrient that is enough for almost every individuals, even someone who has high needs for the nutrient. This level of intake is, therefore, considerably higher than what most people would need. If individuals are consuming the RNI of a nutrient they are most unlikely to be deficient in that nutrient.
RNI values are not given by COMA 1991, however, a safe and adequate level is believed to lie above 25 mcg per day.
Food Sources
The richest known sources of biologically active chromium in nature are, in order, brewer's yeast, black pepper, calf liver, American cheese and wheat germ. However, even brewer's yeast typically contains only 2 micrograms chromium per gram of yeast, less than half of which is in the biologically active GTF form. Other foods containing trace amounts of chromium include:
| Beef | Beef liver |
| Beer | Bran flake |
| Chicken liver | Chicken |
| Chili peppers | Lamb liver |
| Lobster | Mushrooms |
| Oysters | Pork |
| Potato | Shrimp |
| Turkey liver | Whole wheat |
| Wine |
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