1) as it binds to insulin-activated insulin receptors and results in stimulating its tyrosine kinase activity. It is proposed that LMWCr then participates as part of an insulin signal amplification system ( Fig. Binding with chromium ions converts inactive LMWCr to its holo, or active, form. With this step, chromium is transferred from transferrin to LMWCr, which normally exists in insulin-dependent cells in the apo, or inactive, form. The pH of the internalized vesicle is reduced by ATP-driven proton pumps, chromium is released from transferrin, and the resulting free chromium is postulated to be sequestered by LMWCr ( 15, 17). Transferrin containing the plasma-bound chromium is postulated to bind to the transferrin receptors and is internalized by endocytosis ( Figs. It has been suggested that migration of transferrin receptors to the plasma membranes of insulin-insensitive cells after insulin stimulation is the initial step in this process. The principal carrier protein for chromium is transferrin, which also plays a critical role in the movement of chromium from blood to LMWCr. Once absorbed, chromium is distributed to various tissues of the body, but appears to be most concentrated in the kidney, muscle, and liver ( 16). Very little chromium (<2%) in the form of inorganic compounds is absorbed but may be higher with certain organic formulations ( 14). Therefore, normal dietary intake of chromium for adults may be suboptimal. Results from one study ( 10) indicated that daily chromium intakes for men and women in the U.S. However, it appears that Americans normally ingest ∼50–60% of the minimum suggested daily intake of 50 μg ( 7). National Academy of Sciences has established the Recommended Daily Allowances for chromium as 50–200 μg/day for adult men and women ( 11), which is also the Estimated Safe and Adequate Daily Dietary Intake (ESADDI) for chromium for children aged 7 years to adulthood ( 7, 12). Chromium is also present in many multivitamin/mineral supplements, and there are also specific chromium picolinate (CrP) supplements that contain 200–600 μg chromium per tablet ( 10). Trivalent chromium is found in a wide range of foods, including egg yolks, whole-grain products, high-bran breakfast cereals, coffee, nuts, green beans, broccoli, meat, brewer’s yeast, and some brands of wine and beer ( 8, 9). Chromium is now routinely added to TPN solutions ( 5). Other studies ( 4, 5) of the beneficial effects of chromium in patients receiving TPN have also been documented in the scientific literature. In the following 2 weeks, signs and symptoms of diabetes were ameliorated, with markedly improved glycemic status and greatly reduced insulin requirements (exogenous insulin requirements decreased from 45 units/day to none). Based on previous animal studies and preliminary human studies, the patient was given supplemental chromium. A patient receiving total parenteral nutrition (TPN) developed severe signs of diabetes, including weight loss and hyperglycemia that was refractory to increasing insulin dosing ( 3). Interest regarding chromium administration in patients with diabetes was kindled by the observation in the 1970s that it truly was an essential nutrient required for normal carbohydrate metabolism. This factor was eventually suggested to be a biologically active form of trivalent chromium that could substantially lower plasma glucose levels in diabetic mice ( 2). The interest in chromium as a nutritional enhancement to glucose metabolism can be traced back to the 1950s, when it was suggested that brewer’s yeast contained a glucose tolerance factor (GTF) that prevented diabetes in experimental animals ( 1).
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |