Let's Get Serious: How Does Chromium Work?

The Mechanism of Chromium

The evidence for chromium (Cr) as an essential trace mineral in animals was obtained in rats fed a Torula yeast-based diet which developed abnormal glucose tolerance that could be reversed by supplements of brewer's yeast. It was reported that chromium formed a complex with insulin that enhanced insulin's activity (Beers, et al. 2006). However, the relevance of animal studies of chromium deficiency to the effects of chromium in humans remains controversial.

Glucose tolerance factor has never been isolated nor its structure determined. The insulin receptor has been purified and characterized without finding any evidence of chromium as a component of its subunits, as an accessory chromoprotein for insulin binding, or as a second messenger in mediating the effect of insulin on cells. Unlike iron, zinc, copper, molybdenum, and selenium, chromium has not been found in a metalloprotein with biologic activity. Therefore, the apparent biologic activity of chromium in promoting glucose tolerance remains unexplained (Beers, et al. 2006).

One study suggests that chromium potentiates the action of insulin possibly by increasing insulin binding, insulin binding receptor number, improving insulin internalization and increasing insulin sensitivity. (Volpe, et al. 2001) Insulin functions in transporting glucose and amino acids into muscle cells, regulating protein metabolism and synthesis. In another study, researchers suggest that improvements in insulin utilization should theoretically lead to increased muscle mass and reduced body fat (Mertz 1994). The link between these contradictory changes in body composition may be due to chromium’s ability to potentiate insulin’s effects on converting glucose to carbon dioxide or lipid (JB 2000).

According to a review done by Cefalu, chromium, once absorbed, is distributed to various tissues of the body mostly concentrated in the kidney, muscle, and liver by a carrier protein - transferrin. Chromium inhibits phosphotyrosine phosphatase that leads to decrease in insulin sensitivity. The balance between kinase and phosphatase activity may facilitate the role of insulin in rapidly moving glucose into cells (Cefalu and Hu 2004).

References:

• Beers, Mark H MD, Robert S MD Porter, Thomas V MD Jones, Justin L MD Kaplan, and Michael MD Berkwits. The Merck Manual of Diagnosis and Therapy. New Jersey: Merck Research Laboratories, 2006.
• Cefalu, William T MD, and Frank B MD PHD Hu. "Role of Chromium in Human Health and in Diabetes." Diabetes Care, 2004: 2741-2751.
• JB, Vincent. "The biochemistry of chromium." Journal of Nutrition, 2000: 715-718.
• Mertz, M. "Chromium in human nutrition: a review." Journal of Nutrition, 1994: 117-118.
• Volpe, Stella L. PhD, RD, Hui-Wen MS Huang, Kanokwan MS Larpadisorn, and Ingrid I. Lesser. "Effect of Chromium Supplementation and Exercise on Body Composition, Resting Metabolic Rate and Selected Biochemical Parameters in Moderately Obese Women Following an Exercise Program." Journal of the American College of Nutrition, 2001: 293-306.