Chromium is a mineral that humans require in trace amounts, although its mechanisms of action in the body and the amounts needed for optimal health are not well defined. It is found primarily in two forms: 1) trivalent (chromium 3+), which is biologically active and found in food, and 2) hexavalent (chromium 6+), a toxic form that results from industrial pollution. This fact sheet focuses exclusively on trivalent (3+) chromium.
Chromium is known to enhance the action of insulin , a hormone critical to the metabolism and storage of carbohydrate, fat, and protein in the body . In 1957, a compound in brewers' yeast was found to prevent an age-related decline in the ability of rats to maintain normal levels of sugar (glucose) in their blood . Chromium was identified as the active ingredient in this so-called "glucose tolerance factor" in 1959 .
Chromium also appears to be directly involved in carbohydrate, fat, and protein metabolism , but more research is needed to determine the full range of its roles in the body. The challenges to meeting this goal include:
Defining the types of individuals who respond to chromium supplementation;
Evaluating the chromium content of foods and its bioavailability;
Determining if a clinically relevant chromium-deficiency state exists in humans due to inadequate dietary intakes; and
Developing valid and reliable measures of chromium status .
What foods provide chromium?
Chromium is widely distributed in the food supply, but most foods provide only small amounts (less than 2 micrograms per serving). Meat and whole-grain products, as well as some fruits, vegetables, and spices are relatively good sources . In contrast, foods high in simple sugars (like sucrose and fructose) are low in chromium .
Dietary intakes of chromium cannot be reliably determined because the content of the mineral in foods is substantially affected by agricultural and manufacturing processes and perhaps by contamination with chromium when the foods are analyzed . Therefore, Table 1, and food-composition databases generally, provide approximate values of chromium in foods that should only serve as a guide.
What affects chromium levels in the body?
Absorption of chromium from the intestinal tract is low, ranging from less than 0.4% to 2.5% of the amount consumed , and the remainder is excreted in the feces . Enhancing the mineral's absorption are vitamin C (found in fruits and vegetables and their juices) and the B vitamin niacin (found in meats, poultry, fish, and grain products) . Absorbed chromium is stored in the liver, spleen, soft tissue, and bone .
The body's chromium content may be reduced under several conditions. Diets high in simple sugars (comprising more than 35% of calories) can increase chromium excretion in the urine . Infection, acute exercise, pregnancy and lactation, and stressful states (such as physical trauma) increase chromium losses and can lead to deficiency, especially if chromium intakes are already low .
When can a chromium deficiency occur?
In the 1960s, chromium was found to correct glucose intolerance and insulin resistance in deficient animals, two indicators that the body is failing to properly control blood-sugar levels and which are precursors of type 2 diabetes . However, reports of actual chromium deficiency in humans are rare. Three hospitalized patients who were fed intravenously showed signs of diabetes (including weight loss, neuropathy, and impaired glucose tolerance) until chromium was added to their feeding solution. The chromium, added at doses of 150 to 250 mcg/day for up to two weeks, corrected their diabetes symptoms . Chromium is now routinely added to intravenous solutions.
Who may need extra chromium?
There are reports of significant age-related decreases in the chromium concentrations of hair, sweat and blood , which might suggest that older people are more vulnerable to chromium depletion than younger adults . One cannot be sure, however, as chromium status is difficult to determine . That's because blood, urine, and hair levels do not necessarily reflect body stores . Furthermore, no chromium-specific enzyme or other biochemical marker has been found to reliably assess a person's chromium status .
There is considerable interest in the possibility that supplemental chromium may help to treat impaired glucose tolerance and type 2 diabetes, but the research to date is inconclusive. No large, randomized, controlled clinical trials testing this hypothesis have been reported in the United States . Nevertheless, this is an active area of research.
What are some current issues and controversies about chromium?
Chromium has long been of interest for its possible connection to various health conditions. Among the most active areas of chromium research are its use in supplement form to treat diabetes, lower blood lipid levels, promote weight loss, and improve body composition.
Type 2 diabetes and glucose intolerance
In type 2 diabetes, the pancreas is usually producing enough insulin but, for unknown reasons, the body cannot use the insulin effectively. The disease typically occurs, in part, because the cells comprising muscle and other tissues become resistant to insulin's action, especially among the obese. Insulin permits the entry of glucose into most cells, where this sugar is used for energy, stored in the liver and muscles (as glycogen), and converted to fat when present in excess. Insulin resistance leads to higher than normal levels of glucose in the blood (hyperglycemia).
Chromium deficiency impairs the body's ability to use glucose to meet its energy needs and raises insulin requirements. It has therefore been suggested that chromium supplements might help to control type 2 diabetes or the glucose and insulin responses in persons at high risk of developing the disease. A review of randomized controlled clinical trials evaluated this hypothesis . This meta-analysis assessed the effects of chromium supplements on three markers of diabetes in the blood: glucose, insulin, and glycated hemoglobin (which provides a measure of long-term glucose levels; also known as hemoglobin A1C). It summarized data from 15 trials on 618 participants, of which 425 were in good health or had impaired glucose tolerance and 193 had type 2 diabetes. Chromium supplementation had no effect on glucose or insulin concentrations in the non-diabetic subjects nor did it reduce these levels in subjects with diabetes, except in one study. However, that study, conducted in China (in which 155 diabetics were given either 200 or 1,000 mcg/day of chromium or a placebo) might simply show the benefits of supplementation in a chromium-deficient population.
Overall, the value of chromium supplements for diabetics is inconclusive and controversial . Randomized controlled clinical trials in well-defined, at-risk populations where dietary intakes are known are necessary to determine the effects of chromium on markers of diabetes .
The effects of chromium supplementation on blood lipid levels in humans are also inconclusive . In some studies, 150 to 1,000 mcg/day has decreased total and low-density-lipoprotein (LDL or "bad") cholesterol and triglyceride levels and increased concentrations of apolipoprotein A (a component of high-density-lipoprotein cholesterol known as HDL or "good" cholesterol) in subjects with atherosclerosis or elevated cholesterol or among those taking a beta-blocker drug . These findings are consistent with the results of earlier studies .
However, chromium supplements have shown no favorable effects on blood lipids in other studies . The mixed research findings may be due to difficulties in determining the chromium status of subjects at the start of the trials and the researchers' failure to control for dietary factors that influence blood lipid levels .
Body weight and composition
Chromium supplements are sometimes claimed to reduce body fat and increase lean (muscle) mass. Yet a recent review of 24 studies that examined the effects of 200 to 1,000 mcg/day of chromium (in the form of chromium picolinate) on body mass or composition found no significant benefits . Another recent review of randomized, controlled clinical trials did find supplements of chromium picolinate to help with weight loss when compared to placebos, but the differences were small and of debatable clinical relevance . In several studies, chromium's effects on body weight and composition may be called into question because the researchers failed to adequately control for the participants' food intakes. Furthermore, most studies included only a small number of subjects and were of short duration .
What are the health risks of too much chromium?
Few serious adverse effects have been linked to high intakes of chromium, so the Institute of Medicine has not established a Tolerable Upper Intake Level (UL) for this mineral . A UL is the maximum daily intake of a nutrient that is unlikely to cause adverse health effects. It is one of the values (together with the RDA and AI) that comprise the Dietary Reference Intakes (DRIs) for each nutrient.
Supplemental sources of chromium
Chromium is a widely used supplement. Estimated sales to consumers were $85 million in 2002, representing 5.6% of the total mineral-supplement market . Chromium is sold as a single-ingredient supplement as well as in combination formulas, particularly those marketed for weight loss and performance enhancement. Supplement doses typically range from 50 to 200 mcg.
The safety and efficacy of chromium supplements need more investigation. Please consult with a doctor or other trained healthcare professional before taking any dietary supplements.
Chromium supplements are available as chromium chloride, chromium nicotinate, chromium picolinate, high-chromium yeast, and chromium citrate. Chromium chloride in particular appears to have poor bioavailability . However, given the limited data on chromium absorption in humans, it is not clear which forms are best to take.
Chromium intakes and healthful diets
Eating a variety of whole grains, fruits, vegetables, meats, and milk and milk products should provide sufficient chromium. According to the 2005 Dietary Guidelines for Americans, "Nutrient needs should be met primarily through consuming foods. Foods provide an array of nutrients and other compounds that may have beneficial effects on health. In certain cases, fortified foods and dietary supplements may be useful sources of one or more nutrients that otherwise might be consumed in less than recommended amounts. However, dietary supplements, while recommended in some cases, cannot replace a healthful diet."
The Dietary Guidelines for Americans describes a healthy diet as one that:
emphasizes a variety of fruits, vegetables, whole grains, and fat-free or low-fat milk and milk products;
includes lean meats, poultry, fish, beans, eggs, and nuts;
is low in saturated fats, trans fats, cholesterol, salt (sodium), and added sugars; and
stays within your daily calorie needs.
Other useful Minerals information: Zinc | Magnesium | Iodine
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