Chromium (Cr) is an essential nutrient required for normal sugar and
fat metabolism. Chromium functions primarily by potentiating the action of
insulin. Chromium occurs primarily in the trivalent and hexavalent forms;
the form in higher organisms is trivalent. This mineral occurs throughout
the body with highest concentrations in the liver, kidney, spleen and
bone.
Deficiency: Signs of deficiency include impaired
glucose tolerance and elevated circulating insulin. In some studies,
chromium supplementation has reduced total serum cholesterol,
triglycerides and apolipoprotein B and increased HDL-cholesterol.
Diet recommendations: The Estimated Safe and Adequate
Daily Dietary Intake (ESADDI) for adults is 50 to 200 µg. Usual
dietary intakes in the U.S. are about 25 µg/day for women and 33
µg/day for men. Breast-fed infants consume less than 1 µg
Cr/day and the ESADDI for infants is 10 to 40 µg/day. The current
ESADDI for chromium needs to be reevaluated.
Food sources/bioavailability: Meat, poultry, fish and
dairy products are generally low in chromium. Fruits, vegetables whole
grains and seeds are better sources but have variable concentrations.
Processing foods with stainless steel equipment may increase their
chromium concentration, especially if the foods are acidic. In addition,
there are differences in bioavailability and biological activity of the
different complexes found in foods.
Toxicity: Both solubility and oxidation state affect
the potential for toxicity; furthermore, the type of complex may impact
toxicity. Toxic effects are limited primarily to industrial exposure to
hexavalent chromium, which is much more toxic than the trivalent form. The
hexavalent chromium compounds may be carcinogenic. The acidity of the
stomach promotes reduction of hexavalent chromium to the trivalent form.
Most of the chromium absorbed from the gastrointestinal tract is
trivalent. The Reference Dose (RfD) for trivalent chromium is 1 mg/kg/day.
This level is more than 300-fold the upper limit of the ESADDI, making
trivalent chromium one of the least toxic nutrients.
Recent research: Chromium improved glucose tolerance,
insulin and hemoglobin A1c of people in China with Type 2 diabetes.
Similar effects were observed in people with impaired glucose tolerance.
In humans undergoing resistive training, chromium did not consistently
promote a significant increase in strength and lean body mass. In pigs
chromium improved lean body mass and litter size. Immune function in
stressed farm animals was improved by chromium. Sugar-induced increases in
blood pressure of spontaneously hypertensive rats were prevented by
chromium. Chromium increased the phosphorylation of the insulin receptor
leading to enhanced insulin sensitivity.
