Chromium supplement offers diabetes hope - animal study
sensitivity to insulin in obese, insulin-resistant rats - findings
that could have implications for diabetic humans.
Insulin resistance occurs when muscle and fat tissue, for example, react poorly to insulin, the hormone responsible for glucose metabolism. The condition is found in both pre-diabetics and those with fully developed diabetes.
Previous research has shown that chromium supplements could enhance insulin sensitivity by improving receptor signalling, but these had been limited to in vitro studies.
The new study, published in the Journal of Nutrition (Vol 136, pp. 415-420), is the first to use in vivo animal models to demonstrate the mechanism.
"This animal study is significant because it suggests a more detailed mechanism of action for chromium in improving insulin sensitivity in muscle, a major insulin-sensitive tissue," said corresponding author Dr Willian Cefalu from the Pennington Biomedical Research Center, Louisiana.
The randomised study evaluated 11 obese, insulin-resistant male rats (JCR:LA-cp) and 10 lean male rats of the same strain. The rats received either a chromium picolinate supplement (80 micrograms per kg per day) or a placebo for 12 weeks.
"Obese rats treated with chromium picolinate had significantly improved glucose disposal rates and demonstrated a significant increase in insulin-stimulated phosphorylation of insulin receptor substrate (IRS)-1 and phosphatidylinositol (PI)-3 kinase activity in skeletal muscle compared with obese controls," wrote the researchers.
The study has demonstrated that the chromium supplement helped muscle cell insulin-receptor sites to bind insulin. Once the insulin is bound, the cell activates "glucose transporters" to take glucose up from the blood, helping to metabolize glucose at a steady rate.
No effects, either positive or negative, were observed in the lean, healthy rats with the doses used in this study.
"These results add to a growing body of evidence, but more importantly provide a cellular mechanism to explain the effects of chromium picolinate on carbohydrate metabolism," said Cefalu.
Nutrition 21, maker and supplier of the picolinate form of chromium, announced the start of a clinical trial in early 2005 to study type-1 diabetics aged between 12 and 18 supplemented with 600 micrograms per day.
The British Food Standards Agency (FSA) set the maximum upper limit of chromium picolinate at 10 mg per day, well above the level commonly used in studies.
Matt Hunt, Science Information Officer for British charity Diabetes UK, welcomed the research, and told NutraIngredients.com that it was of general interest and supported current understanding of this field.
However, Hunt added: "Unlike other essential trace metals, chromium has not been found in a metalloprotein with biological activity. Therefore, the functional basis for the chromium requirement in the diet remains unexplained."
"Chromium deficiency is a disorder that results from an insufficient dietary intake of chromium. It occurs rarely in developed nations," said Hunt.
An estimated 19 million people are affected by diabetes in the EU, equal to four per cent of the total population. This figure is projected to increase to 26 million by 2030.
In the US, there are over 20 million people with diabetes, equal to seven per cent of the population. The total costs are thought to be as much as $132 billion, with $92 billion being direct costs from medication, according to 2002 American Diabetes Association figures.
