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Citrus peel extract shows benefits for diabetes

By Stephen Daniells , 19-Jun-2006

A daily supplement of an extract from citrus peel could reduce insulin resistance in hamsters, suggesting the extract might also help prevent diabetes in humans, says a North American study.

The citrus peel extracts, polymethoxylated flavones (PMFs), have been reported to have beneficial effects on cholesterol-levels, but this is said to be the first study that looks in detail at the benefits and reports that the extracts have positive effects on inflammatory cytokine levels.

"This study provides novel evidence that PMF reverse hypertriglyceridimia and restores insulin sensitivity," said researchers from the University of Hawaii, in collaboration with KGK Synergize, a Canadian nutraceutical company.

PMFs are similar to other plant pigments found in citrus fruits that have been increasingly linked to health benefits, including protection against cancer, heart disease and inflammation. The main PMFs in the extracts are tangeretin and nobiletin, as well as small amounts of synephrine.

The new study, published in the journal Life Sciences (Vol. 79, pp. 365-373), investigated the effects of a daily supplement of PMF on insulin resistant hamsters.

Twenty-eight hamsters were fed a fructose-rich diet for two weeks to induce hypertriglyceridimia and insulin resistance. The animals were then divided into four equal groups and fed one of four diets: chow; control fructose diet; fructose plus low dose PMF (62.5 mg/kg body weight per day); fructose plus high dose PMF (125 mg/kg/day).

After four weeks of the test diets, the researchers found that both PMF groups showed a significantly decrease in serum triglycerides (TG) and cholesterol levels compared to the fructose-fed hamsters.

The decreases in TG were limited to the heart (33 per cent for the 125 mg PMF group) and liver (42 per cent for the 125 mg PMF group), with no changes observed in the epididymal fat and muscle.

"After PMF supplementation for four weeks, significant reductions in TG and cholesterol were observed in a dose-dependent manner related to lipids, cholesterol and inflammation, indicating that the response was specific to PMFs," wrote lead author Rachel Li.

Because insulin resistance, diabetes, and obesity are recognized as inflammatory disorders, say the researchers, they measured concentrations of the mediators for inflammation, tumour necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6), and markers of immune response, the cytokine IFN-gamma.

The researchers found decreased levels of these biomarkers in the PMF supplemented groups and the effect appeared to be dose-dependent.

"The mechanism of PMF in improving insulin sensitivity in this study can be explained, at least in part, by its regulatory effects on cytokines," said Li.

"These data provide a basis for further investigation of the role of PMF in improving insulin resistance (IR) in human subjects and for testing dietary reagents for the prevention of IR," concluded the researchers.

An estimated 19m people are affected by diabetes in the EU 25, equal to four per cent of the total population. This figure is projected to increase to 26m by 2030.

In the US, there are over 20m people with diabetes, equal to seven per cent of the population. The total costs are thought to be as much as $132bn, with $92bn being direct costs from medication, according to 2002 American Diabetes Association figures.

The American Heart Association of Hawaii and the NIH-National Center for Complementary and Alternative Medicine funded the study.

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