Chromium is an essential trace mineral in human nutrition. Dietary chromium is required for the correct function of the insulin system. It is not fully understood how chromium functions at the cellular level, but a number of hypotheses have been suggested. Chromium forms a complex with nicotinic acid and some amino acids to form the glucose tolerance factor (GTF). This glucose tolerance factor has been hypothesised to bridge the gap between insulin and its receptor, thus facilitating the signal from hormone to cell. Other potential functions may include a direct effect on insulin release from the pancreas, an ability to increase the fluidity of cell membranes, and thus improve the internalisation of the insulin signal from the interior of the cell, as well as a direct effect on the expression of insulin receptor numbers. Animal models show that chromium deficient diets cause the development of insulin resistance and ultimately diabetes.
Individuals consuming chromium supplements have a lower odds of having type 2 diabetes. This does not prove that the chromium is the beneficial agent, and there may be other nutrients in the supplements that aid health. In addition, those taking a supplement are more likely to consume a healthy diet or have other lifestyle factors that reduce disease risk. However, animal models are clear. Chromium deficiencies cause diabetes in mammals.
Results from human clinical trials using chromium have been inconsistent, and this likely relates to poor study design. It is very difficult to control human diets and behaviour and the number of variables makes some nutritional studies difficult to assess. However, animals models are far clearer, and deliberately feeding mammals chromium deficient diets does induce diabetes. These symptoms are then reversed by addition of chromium back to the diet. A recent epidemiological study investigated the association between chromium intake and type 2 diabetes risk in over 60,000 subjects living in the United States. The results of the study showed that 28.8 % of the subjects consumed a chromium containing supplement in the previous 30 days. Those who consumed a chromium containing supplement in the previous 30 days had a significantly lower odds of having type 2 diabetes compared to those who did not consume a chromium containing supplement. However, this does not prove cause and effect.
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