Although chromium is accepted as nutritionally essential for animals and humans, an understanding of the mechanism of its biological action and the amount of chromium needed for health and optimal function remains elusive. Chromium apparently potentiates the action of insulin in glucose utilization and protein anabolism (1,2). Because there are insufficient appropriate biochemical measures of chromium nutritional status and of the content and the bioavailability of chromium from foods, there is, unfortunately, a paucity of information that describes who would benefit from increased dietary chromium.
Controlled studies to determine chromium bioavailability and the effects of graded intakes of dietary chromium are hampered by the lack of data on the chromium content of feed components and individual foods. Furthermore, sensitive and specific biochemical and functional measures that respond to graded chromium intake are also insufficient. These limitations, as well as differences in experimental designs, contribute to the lack of consensus in reported findings of biochemical, functional, and structural effects of supplemental chromium in animals and humans. Despite this, evidence is accumulating that chromium is essential to insulin action, particularly glucose homeostasis. Intakes of fewer than 50 mcg/day have been reported for adults living in the United Kingdom, Finland, Canada, and New Zealand (3).
Signs of chromium deficiency have been reported in mammals and centre on disturbances involving insulin insensitivity (4). The signs and symptoms of chromium deficiency in mammals are as follows: impaired glucose tolerance, elevated circulating insulin concentration, fasting hyperglycaemia, impaired growth, elevated circulating cholesterol and triglyceride concentrations, neuropathy, increased intraocular pressure, decreased insulin binding, decreased insulin receptor number, and impaired humoral immune response. Studies have confirmed marked improvement in glucose tolerance with chromium supplements (5-7).
Chromium has been implicated in two additional physiological functions. Preliminary evidence suggests that an interaction between chromium and thyroid function occurs in animals and humans (8). However, the physiological significance and mechanism of this interaction have not been studied. Chromium also has been involved in protein metabolism.
Sources of Chromium
Processed meats, whole-grain products, ready-to-eat bran cereals, green beans, broccoli, and spices have a high concentration of chromium. Foods high in simple sugars such as fructose, which is found in soft drinks, and sucrose, or table sugar, are not only low in chromium content, they also promote chromium losses. Chromium intakes are adequate in diets high in fruits, vegetables, and whole-grains and low in simple sugars. Although chromium exists in nature in oxidation states from Chromium−2 to Chromium-6, the predominant forms are Chromium-3 and Chromium-6. Bound to oxygen, Chromium-6 is a strong oxidizing agent that is readily reduced to Chromium-3 in an acidic environment, such as the stomach.
Chromium absorption and utilization are impacted by other dietary factors. Amino acids chelate with dietary chromium, prevent precipitation in the alkaline milieu of the small intestine, and thus enhance chromium absorption. Phytate also forms chelates with chromium, and these complexes inhibit uptake of Chromium across the intestine. Oxalate, which is found in vegetables and grains, significantly increases chromium uptake. In humans, ascorbic acid promotes chromium absorption, as does nicotinic acid.
Glucose tolerance factor (GTF), was proposed to include chromium, nicotinic acid, and possibly the amino acids glycine, cysteine, and glutamic acid, but, the defined structure of GTF and whether it is the most biologically active form of chromium remain controversial.
Chromium in health and disease
Chromium supplementation apparently improves glucose utilization and decreases exogenous insulin requirements in patients with glucose intolerance and insulin resistance. The effects depend on the degree of glucose intolerance and the form, amount, and duration of the chromium supplementation. (9). Sixty days of supplementation with 500 mcg of chromium/day as chromium chloride, resulted in significantly lowered glucose and insulin after a glucose challenge in 12 maturity-onset diabetics (10). Doisy et al (11) found that supplemental brewer’s yeast decreased the need for exogenous insulin by insulin-dependent diabetics. Ravina et al (12) also found that 200 mcg of chromium as chromium picolinate improved glucose control in diabetic patients.
Chromium supplementation may also normalize blood glucose in adults who have a tendency toward impaired glucose utilization. Data suggest that chromium may normalize blood glucose concentrations in adults with tendencies toward moderate hyperglycaemia and hypoglycaemia but has no effect on individuals with normal blood glucose concentrations. Other studies have provided support for these initial findings (13-15)
Glucose tolerance improved in older adults characterized as at-risk for hyperglycaemia after diet supplementation with chromium, as brewer’s yeast or chromium chloride, for periods ranging from several weeks to a few months (16,17). In contrast, elderly people not at risk who received either 5 g of brewer’s yeast (equivalent to 200 mcg of Chromium) or 200 mcg of chromium as chromium chloride, experienced no changes in glucose or insulin (18). These findings indicate that supplemental chromium can improve glucose utilization in some adults. Perhaps this improvement in glucose homeostasis occurs in individuals with low chromium nutritional status.
Reports suggest that chromium picolinate improves insulin utilization in non–insulin-dependent diabetic patients (19).
Chromium picolinate supplementation was shown recently to improve glucose homeostasis in type 2 diabetic patients (20).
Supplemental chromium was associated with significant decreases in serum total cholesterol, but there were no changes in triglyceride or high-density lipoprotein cholesterol. The beneficial effects of supplemental chromium became apparent at chromium intakes exceeding recommendations for the general population.
Supplemental chromium causes significant decreases in serum total cholesterol concentration with larger decreases observed in subjects with the highest concentration prior to supplementation (21). Riales & Albrink (22) found no change in serum total cholesterol but did find a significant increase in high-density lipoprotein cholesterol and a decrease in triglyceride concentrations after 12 weeks of supplementation with 200 mcg of chromium as chromium Cl3. This finding is consistent with other reports (23,24).
Body Composition and Exercise
The vast majority of studies have examined the effect of chromium supplementation, in the form of chromium picolinate, with concurrent resistive exercise. The first study involved ten male college students who were randomly assigned to receive either 200 mcg of chromium as chromium picolinate or a placebo daily for 40 days while participating in weight training (25). At the end of six weeks of chromium supplementation and exercise training, body weight decreased 1.2 kg, free fat mass (FFM) increased 2.6 kg, and fat mass (FM) decreased 3.4 kg. In contrast, the men who received the placebo showed no significant changes until after six weeks, when they gained 1.8 kg in FFM and lost 1.0 kg of FM.
However, other studies have failed to confirm that chromium picolinate supplementation promotes positive changes in body composition during resistance training (26,276).
The data seems to indicate that when dietary chromium meets population standards for adequate intake, supplemental chromium has no independent effect on performance and body composition in weight-stable adults. However, as noted above, levels of chromium in UK tend to be lower than recommended.
Chromium picolinate supplementation has been shown to result in significantly higher positive (i.e. beneficial) changes in body composition improvement compared with results from the placebo (28). The interpretation of this finding was that Chromium picolinate enhanced both FFM retention and loss of FM. In a second study, 122 free-living adults consumed a capsule containing either 400 mcg of chromium daily as chromium picolinate or a placebo for 90 days (29). After controlling for presumable differences in caloric intake and output, as compared with the placebo group, the subjects with chromium-supplemented diets lost significantly more weight (7.8 vs 1.8 kg) and FM (7.7 vs 1.5 kg) without loss of FFM.
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Keywords:-chromium, glucose intolerance, hyperlipidaemia, body composition, exercise, weight loss