Although trivalent chromium is recognized as a nutritionally essential mineral, scientists are not yet certain exactly how it functions in the body. The two most common forms of chromium are trivalent chromium and hexavalent chromium. Chromium is the principal form in foods, as well as the form utilized by the body. Chromium is derived from chromium by heating at alkaline pH and is used as a source of chromium for industrial purposes. It is a strong irritant and is recognized as a carcinogen when inhaled. At low levels, chromium is readily reduced to chromium by reducing substances in foods and the acidic environment of the stomach, which serve to prevent the ingestion of chromium.
A biologically active form of chromium participates in glucose metabolism by enhancing the effects of insulin. Insulin is secreted by specialized cells in the pancreas in response to increased blood glucose levels, for example, after a meal. Insulin binds to insulin receptors on the surface of cells, activating those receptors and stimulating glucose uptake by cells. Through its interaction with insulin receptors, insulin provides cells with glucose for energy and prevents blood glucose levels from becoming elevated. In addition to its effects on carbohydrate (glucose) metabolism, insulin also influences the metabolism of fat and protein. A decreased response to insulin or decreased insulin sensitivity may result in impaired glucose tolerance or type 2 diabetes, also known as non-insulin dependent diabetes mellitus (NIDDM). Type 2 diabetes is characterized by elevated blood glucose levels and insulin resistance.
The precise structure of the biologically active form of chromium is not known. Recent research suggests that a low-molecular-weight chromium-binding substance (LMWCr) may enhance the response of the insulin receptor to insulin. The following is a proposed model for the effect of chromium on insulin action (diagram). First, the inactive form of the insulin receptor is converted to the active form by binding insulin. The binding of insulin by the insulin receptor stimulates the movement of chromium into the cell and results in binding of chromium to apoLMWCr, a form of the LMWCr that lacks chromium. Once it binds chromium the LMWCr binds to the insulin receptor and enhances its activity. The ability of the LMWCr to activate the insulin receptor is dependent on its chromium content. When insulin levels drop due to normalization of blood glucose levels, the LMWCr may be released from the cell in order to terminate its effects.
Chromium deficiency was reported in three patients on long-term intravenous feeding who did not receive supplemental chromium in their intravenous solutions. These patients developed evidence of abnormal glucose utilization and increased insulin requirements that responded to chromium supplementation. Additionally, impaired glucose tolerance in malnourished infants responded to an oral dose of chromium chloride. Because chromium appears to enhance the action of insulin and chromium deficiency has resulted in impaired glucose tolerance, chromium insufficiency has been hypothesized to be a contributing factor to the development of Type 2 diabetes.
Several studies of male runners indicated that urinary chromium loss was increased by endurance exercise, suggesting that chromium needs may be greater in individuals who exercise regularly. In a more recent study, resistive exercise (weight lifting) was found to increase urinary excretion of chromium in older men. However, chromium absorption was also increased, leading to little or no net loss of chromium as a result of resistive exercise. At present, research on the effects of inadequate chromium intake and risk factors for chromium insufficiency are limited by the lack of sensitive and accurate tests for determining chromium nutritional status.
Impaired glucose tolerance and type 2 (non-insulin dependent) diabetes: in 12 out of 15 controlled studies of people with impaired glucose tolerance, chromium supplementation was found to improve some measure of glucose utilization or to have beneficial effects on blood lipid profiles. Impaired glucose tolerance refers to a metabolic state between normal glucose regulation and overt diabetes. Generally, blood glucose levels are higher than normal, but lower than those accepted as diagnostic for diabetes. Impaired glucose tolerance is associated with increased risk for cardiovascular diseases but is not associated with the other classic complications of diabetes. About 25% to 30% of individuals with impaired glucose tolerance eventually develop type 2 diabetes. Generally, chromium supplementation at doses of about 200 mcg/day, in a variety of forms for two to three months were found to be beneficial. The reasons for the variation or lack of effect in some studies are not clear, but chromium depletion is not the only known cause of impaired glucose tolerance. Additionally, the lack of an accurate measure of chromium nutritional status prevents researchers from identifying those individuals who are most likely to benefit from chromium supplementation.
Cardiovascular diseases: impaired glucose tolerance and type 2 diabetes are associated with adverse changes in lipid profiles and increased risk of cardiovascular diseases. Studies examining the effects of chromium supplementation on lipid profiles have been notable for their inconsistent results. While some studies have observed reductions in serum total cholesterol, LDL-cholesterol, and triglyceride levels or increases in HDL-cholesterol levels, others have observed no effect. Such inconsistent responses of lipid and lipoprotein levels to chromium supplementation may reflect differences in chromium nutritional status. It is possible that only those individuals with insufficient chromium will experience beneficial effects on lipid profiles due to chromium supplementation.
Increases muscle mass: Claims that chromium supplementation increases lean body mass and decreases body fat are based on the relationship between chromium and insulin action (see Function). In addition to affecting glucose metabolism, insulin is known to affect fat and protein metabolism. At least 12 placebo-controlled studies have compared the effect of chromium supplementation (200-1,000 mcg as chromium picolinate/day) with or without an exercise program on lean body mass and measures of body fat. In general, those studies that have used the most sensitive and accurate methods of measuring body fat and lean mass (dual energy x-ray absorbtiometry or DEXA and hydrodensitometry or underwater weighing) do not indicate a beneficial effect of chromium supplementation on body composition.
Promotes weight loss: Controlled studies of chromium supplementation (200-400 mcg as chromium picolinate/day) have demonstrated little if any beneficial effect on weight or fat loss, and claims of weight loss in humans appear to be exaggerated. In 1997 the U.S. Federal Trade Commission (FTC) ruled that there is no basis for claims that chromium picolinate promotes weight loss and fat loss in humans.
Type 2 (non-insulin dependent) diabetes: is characterized by elevated blood glucose levels and insulin resistance. Although insulin levels in type 2 diabetics may be higher than in healthy individuals, the physiological effects of insulin are reduced. Because chromium is known to enhance the action of insulin, the relationship between chromium nutritional status and type 2 diabetes has generated considerable scientific interest. Individuals with type 2 diabetes have been found to have higher rates of urinary chromium loss than healthy individuals, especially those with diabetes of more than 2 years duration. Prior to 1997, well-designed studies of chromium supplementation in individuals with type 2 diabetes showed no improvement in blood glucose control, though they provided some evidence of reduced insulin levels and improved blood lipid profiles. In 1997, the results of a placebo-controlled trial conducted in China indicated that chromium supplementation might be beneficial in the treatment of type 2 diabetes. One hundred eighty participants took either a placebo, 200 mcg/day, or 1,000 mcg/day of chromium in the form of chromium picolinate.
At the end of four months, blood glucose levels were 15%-19% lower in those that took 1,000 mcg/day compared with those that took a placebo. Blood glucose levels in those that took 200 mcg/day did not differ significantly from those that took a placebo. Insulin levels were lower in those who took either 200 mcg/day or 1,000 mcg/day. Glycosylated hemoglobin levels, a measure of long-term control of blood glucose, were also lower in both chromium-supplemented groups, but they were lowest in the group taking 1,000 mcg/day. Because the chromium nutritional status of the Chinese participants was not evaluated, and the prevalence of obesity was much lower than is typically associated with type 2 diabetics in the U.S., extrapolation of these results to a U.S. population is difficult. However, the findings in the Chinese population emphasize the need for large-scale randomized controlled trials of chromium supplementation for type 2 diabetes in the U.S.
Gestational diabetes: few studies have examined the effects of chromium supplementation on gestational diabetes. Gestational diabetes occurs in about 2% of pregnant women and usually appears in the second or third trimester of pregnancy. Blood glucose levels must be tightly controlled to prevent adverse effects on the developing fetus. After delivery, glucose tolerance generally reverts to normal. However, 30% to 40% of women who have had gestational diabetes develop type 2 diabetes within 5 to 10 years. An observational study in pregnant women did not find serum chromium levels to be associated with measures of glucose tolerance or insulin resistance in late pregnancy, although serum chromium levels may not reflect tissue chromium levels. Women with gestational diabetes whose diets were supplemented with 4 mcg of chromium per kilogram of body weight daily as chromium picolinate for 8 weeks had decreased fasting blood glucose and insulin levels compared with those who took a placebo. However, insulin therapy rather than chromium picolinate was required to normalize severely elevated blood glucose levels.
Chromium Used to Help Blood Sugar, Metabolism. November 21, 2005.
Chromium is an essential trace mineral found in a variety of foods, including whole grains, cereals, spices (such as black pepper), broccoli, mushrooms, cheese, seafood and meat. In the body, it plays a role in metabolizing fats and carbohydrates and controlling blood levels of sugar.
The body has a hard time absorbing chromium supplements in mineral form; it is absorbed more easily when it's bound to another molecule. Chromium niacin, sometimes called niacin-bound chromium, is one form of so-called bioavailable chromium sold as a supplement: Another commonly sold form is chromium picolinate.
Uses: Chromium niacin (also known as chromium polynicotinate) and chromium picolinate are often taken for diabetes, weight loss, body building or, sometimes, to prevent heart disease.
Dose: The Institute of Medicine recommends a daily chromium intake of 25 to 45 micrograms. Most people get about 25 micrograms from food: Nutrition experts think that's sufficient (breastfeeding moms may need 45 micrograms). Supplement manufacturers recommend doses of 50 to 200 micrograms a day.
Precautions: The long-term safety of taking high doses of chromium is unknown. Chromium niacin appears safe in manufacturer-recommended doses but chromium picolinate has been linked to a few cases of kidney failure and liver damage. Animal studies suggest chromium picolinate has cancer-causing potential.
Research: In lab studies, animals deprived of chromium become glucose intolerant: Their bodies fail to efficiently remove sugar from their blood. Research published in the late 1970s showed that people deprived of chromium developed diabetes-like symptoms, which were reversed following chromium supplementation. But the supplements won't necessarily help people who aren't chromium-deprived. A 2002 review of 15 clinical trials, published in the American Journal of Clinical Nutrition, concluded that the supplement didn't improve glucose or insulin levels in people with Type 2 diabetes. Animal tests have suggested chromium may help lower cholesterol levels and protect against heart disease. Human findings are mixed: A 2005 study published in the American Journal of Epidemiology linked low chromium levels to increased heart disease risk in men.
Dozens of studies on chromium picolinate and weight control are inconclusive: Some have reported that the supplement helps with weight loss, others that it doesn't. Chromium niacin's role in weight loss is less studied. A small clinical trial in India, published in 2004 in the journal Diabetes, Obesity and Metabolism, showed that chromium niacin, taken with hydroxycitric acid and the herb Gymnema sylvestre for eight weeks, decreased body weight by an average of 5% in obese subjects. More studies are needed to confirm this effect.
1. Anderson RA, Cheng N, Bryden NA, Polansky MM, Cheng N, Chi J, Feng J. Elevated intakes of supplemental chromium improve glucose and insulin variables in individuals with type 2 diabetes. Diabetes. 1997 Nov;46(11):1786-91.
Chromium is an essential nutrient involved in normal carbohydrate and lipid metabolism. The chromium requirement is postulated to increase with increased glucose intolerance and diabetes. The objective of this study was to test the hypothesis that the elevated intake of supplemental chromium is involved in the control of type 2 diabetes. Individuals being treated for type 2 diabetes (180 men and women) were divided randomly into three groups and supplemented with: 1) placebo, 2) 1.92 micromol (100 microg) Cr as chromium picolinate two times per day, or 3) 9.6 micromol (500 microg) Cr two times per day. Subjects continued to take their normal medications and were instructed not to change their normal eating and living habits. HbA1c values improved significantly after 2 months in the group receiving 19.2 pmol (1,000 microg) Cr per day and was lower in both chromium groups after 4 months (placebo, 8.5 +/- 0.2%; 3.85 micromol Cr, 7.5 +/- 0.2%; 19.2 micromol Cr, 6.6 +/- 0.1%). Fasting glucose was lower in the 19.2-micromol group after 2 and 4 months (4-month values: placebo, 8.8 +/- 0.3 mmol/l; 19.2 micromol Cr, 7.1 +/- 0.2 mmol/l).
Two-hour glucose values were also significantly lower for the subjects consuming 19.2 micromol supplemental Cr after both 2 and 4 months (4-month values: placebo, 12.3 +/- 0.4 mmo/l; 19.2 micromol Cr, 10.5 +/- 0.2 mmol/l). Fasting and 2-h insulin values decreased significantly in both groups receiving supplemental chromium after 2 and 4 months. Plasma total cholesterol also decreased after 4 months in the subjects receiving 19.2 micromol/day Cr. These data demonstrate that supplemental chromium had significant beneficial effects on HbA1c, glucose, insulin, and cholesterol variables in subjects with type 2 diabetes. The beneficial effects of chromium in individuals with diabetes were observed at levels higher than the upper limit of the Estimated Safe and Adequate Daily Dietary Intake.
2. Morris BW, MacNeil S, Hardisty CA, Heller S, Burgin C, Gray TA. Chromium homeostasis in patients with type II (NIDDM) diabetes. J Trace Elem Med Biol. 1999 Jul;13(1-2):57-61.
The purpose of this study was to assess chromium handling in non-insulin dependent diabetic patients (NIDDM) compared to healthy volunteers. Chromium handling was evaluated using fasting blood and second morning void urine samples from 93 NIDDM patients and 33 healthy volunteers. Significant differences in chromium homeostasis were seen between patients and controls. NIDDM patients had mean levels of plasma chromium around 33% lower and urine values almost 100% higher than those found in health. Healthy volunteers showed a significant negative correlation between fasting levels of plasma chromium and insulin. This was not evident in NIDDM patients. In the early years of onset of NIDDM, plasma chromium values were inversely correlated with plasma glucose. This was lost in patients with diabetes of more than 2 years duration. We suggest large losses of chromium over many years may exacerbate an already compromised chromium status in NIDDM patients and might contribute to the developing insulin resistance seen in patients with type 2 diabetes.
3. A scientific review: the role of chromium in insulin resistance. Diabetes Educ. 2004;Suppl:2-14.
Chromium is an essential mineral that appears to have a beneficial role in the regulation of insulin action and its effects on carbohydrate, protein and lipid metabolism. Chromium is an important factor for enhancing insulin activity. Studies show that people with type 2 diabetes have lower blood levels of chromium than those without the disease. Insulin resistance is the common denominator in a cluster of cardiovascular disease risk factors. One out of every five Americans has metabolic syndrome. It affects 40% of people in their 60s and 70s. Insulin resistance, with or without the presence of metabolic syndrome, significantly increases the risk of cardiovascular disease. Insulin resistance is present in two serious health problems in women; polycystic ovarian syndrome (PCOS) and gestational diabetes. Several studies have now demonstrated that chromium supplements enhance the metabolic action of insulin and lower some of the risk factors for cardiovascular disease, particularly in overweight individuals. Chromium picolinate, specifically, has been shown to reduce insulin resistance and to help reduce the risk of cardiovascular disease and type 2 diabetes. Dietary chromium is poorly absorbed. Chromium levels decrease with age. Supplements containing 200-1,000 mcg chromium as chromium picolinate a day have been found to improve blood glucose control. Chromium picolinate is the most efficacious form of chromium supplementation. Numerous animal studies and human clinical trials have demonstrated that chromium picolinate supplements are safe.
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