Chromium is a naturally occurring element that is found in plants, rocks, soil, and animals. It is an important trace element, with the human body containing about 6 mg of chromium. Chromium exists in diet both as organic and inorganic complexes. It is absorbed in the small intestine mucosa. Absorption is low and is enhanced by vitamin C and vitamin B. Storage of the absorbed chromium occurs in the liver, spleen, bone and soft tissue. Chromium occurs in three valence states, divalent Chromium (II), trivalent chromium (III) and hexavalent chromium (VI). Of the three forms, trivalent chromium is the biologically active compound and is derived from food sources. Notably, chromium is biologically active as part of an oligopeptide known as chromodulin. One of the biological functions of chromium is that it interacts with thyroid metabolism in humans.
Notably, trivalent Cr is the most stable form in biological systems since it does not penetrate biological membranes easily. It is required in the body in trace amounts. On the other hand, hexavalent chromium is toxic both to the environment and the body since it can easily penetrate cellular membranes to damage lipids, proteins and DNA hence carries a high health risk. Divalent chromium, Cr 2 functions as a strong reducing agent. It is readily oxidized to Cr3. This is the reason why divalent Cr does not exist in biological systems. As such, trivalent chromium is the nutritionally useful form of chromium.
First, chromium plays a role in the regulation of blood glucose levels by increasing insulin receptors and insulin-receptor interaction. It does this by enhancing the action of insulin, which functions to reduce the blood glucose levels. Trivalent chromium can therefore be used to correct glucose intolerance and insulin resistance as demonstrated in animal experiments. It also influences the metabolism of carbohydrate, fat and protein. As such, trivalent chromium is useful in achieving glucose tolerance.
Trivalent chromium is also directly involved in the metabolism of fats, carbohydrates and proteins. It also helps in reducing the total and low-density lipoprotein (LDL) as well as the triglyceride levels as part of lipid metabolism in individuals with elevated cholesterol. Additionally, studies have shown that it helps increase the levels of apolipoprotein A, a component of high density lipoprotein, which forms good cholesterol. It also increases transcription thus promoting protein synthesis. Through its action on insulin it can also influence lipid metabolism. Therefore, chromium has the ability to lower LDL levels and increase the HDL levels especially in people with high cholesterol levels. Therefore, chromium may be used to achieve a lean body mass and reduce body fat.
Chromium also takes part in hormonal regulation. For instance, it acts as a co-factor of insulin. Chromium potentiates the effect of insulin by facilitating insulin biding to the receptors on the cell surface. Notably, Cr demand increases during conditions of stress. Elevated cortisol levels during stress act as an antagonist to insulin leading to increased blood glucose concentration and reduction in glucose use by peripheral tissues. Consequently, there is mobilization of Cr reserves. The ability to change sensitivity on insulin also has a role in reproduction.
Chromium has an immune function as well. It has intracellular and intercellular action through potentiating effects of humoral and cellular immunity. In addition, niacin bound trivalent Cr has shown a cardioprotective function and also increases energy levels. However, in high concentrations chromium is cardiotoxic.
Some of the dietary sources of chromium include meat, whole grain products, some fruits and vegetables. Foods containing simple sugars such as sucrose and fructose are low in chromium. It is worth noting that all forms of chromium can be toxic at high levels. However, hexavalent Cr is more toxic than trivalent Cr as aforementioned. Inhalation of high levels of hexavalent Cr causes irritation to the lungs, nose, lung and stomach.