Explain about the Chromium Metabolism?

Chromium appears to be absorbed throughout the small intestine, with absorption being higher in jejunum. The mechanism of absorption has not been well defined but appears to involve processes other than simple diffusion. At normal dietary intakes (10-40 mcg/day), the absorption ranges from 0.4 to 3.0% with absorption being higher at lower intakes. As you have studied for other minerals, even in the case of chromium, an inverse relation between intake and absorption appears to be a basal control mechanism to maintain the body levels of chromium. As compared to healthy individuals, insulin-dependent diabetic patients absorb 2-4 times more chromium. It appears that these patients have an impaired ability to convert inorganic form to usable form and therefore require higher chromium. Like other trace minerals, absorption of chromium is also influenced by some factors. Enhancers and inhibitors are listed in the Table.

Table: Factors influencing absorption

After absorption, chromium binds to plasma proteins for transportation. Both transferrin and albumin are capable of binding absorbed Cr. It has been suggested that transferrin is the main binder of newly absorbed chromium and albumin assumes the role of chromium acceptor and transporter if transferrin binding sites are unavailable. You have studied that transferrin has two metal binding sites, one is primarily for iron and the second is involved in chromium transport. During conditions of iron excess or iron overload such as iron storage diseases, all the metal transport sites on transferrin are occupied by iron. This may explain the high incidence of diabetes in haemochromatosis patients, which may be induced by chromium deficiency. Although transferrin and albumin play the major roles in transportation, other plasma proteins such as α and β globulins and lipoproteins are also involved. As you will go through the next section on 'Functions', you will realize that only organically complexed chromium i.e. GTF is active. It appears that absorbed inorganic chromium is transported to the liver, which is postulated to be the possible site for synthesis of metabolically active molecule. This molecule is held in a body pool and released as needed. Most ingested chromium is excreted in faeces. Inorganic chromium is excreted primarily by the kidney, with small amounts being excreted through hair, sweat and bile. Organically bound chromium is excreted through bile. The biologically active form of chromium performs several functions; the important ones are being subsequently discussed.