The Daily Mail reported today that eating tangerines could protect against heart attacks, diabetes and stroke, as well as staving off obesity.
The newspaper said that researchers have identified a flavonoid chemical in tangerines called nobiletin. Flavonoids are found in various foods, and much study has been made of their possible antioxidant, anti-inflammatory and anti-cancer properties. The current study fed two groups of mice a ‘Western’ diet high in fat and sugar, adding concentrated nobiletin to the food of one group.
The researchers report that the mice given nobiletin did not gain excess weight, get a fatty liver, or have elevated blood sugar or blood fats. The nobiletin mice also had less fatty build-up in the arteries (atherosclerosis), which leads to heart and vascular disease in humans. When nobiletin was directly applied to human liver cells, the cells secreted less ‘bad’ fats.
This is early research. Much further study is needed into how and why this substance works in mice and cells, whether the same would be seen if the chemical were consumed by humans, and how much of it would be needed to have an effect. Eating lots of tangerines is probably not the most appropriate way of consuming this chemical.
Where did the story come from?
The study was carried out by researchers from The University of Western Ontario. Funding was provided by the Heart and Stroke Foundation of Ontario and the Pfizer Canada Cardiovascular Research Program. The study was published in the peer-reviewed medical journal Diabetes .
What kind of research was this?
This study assessed the action of the flavonoid nobiletin when fed to mice that were genetically engineered to make them susceptible to insulin resistance (glucose intolerance) and the development of atherosclerosis. This, in effect, was a mouse model of the human condition of metabolic syndrome. This is a group of risk factors (including obesity, insulin resistance and raised blood sugar, raised blood pressure and raised cholesterol) that increase a person’s risk of developing heart disease, stroke and type 2 diabetes.
As glucose intolerance and type 2 diabetes have been demonstrated to be associated with an overproduction of very-low-density-lipoprotein (VLDL – bad fat) in liver cells, the researchers also examined the effects of nobiletin when applied directly to human liver cells in the laboratory.
What did the research involve?
The mice were genetically engineered to lack an LDL lipoprotein receptor involved in complex chemical pathways that help to take up and break down the bad fats. The mice were divided into groups and either fed a high-fat Western diet, or the same diet supplemented with two different concentrations of nobiletin. Body weight was measured regularly, and at the end of the experimental period (diet periods of both 8 and 26 weeks were tested) blood and tissue samples were taken for assessment of VLDL secretion from the liver cells, atherosclerosis in the blood vessels, body fat, energy expenditure and glucose balance.
In the experiments with human cells, the researchers incubated human liver cells with either nobiletin or insulin. Laboratory methods were then used to assess the chemical reactions that were taking place within the cells, and measure the secretion of VLDL from the cells.
What were the basic results?
In mice that were fed the nobiletin-supplemented diet, there was a reduction in the secretion of VLDL. Tests also showed that the fat did not accumulate in the mice liver cells. Nobiletin also increased the sensitivity of body tissues to the actions of insulin and improved glucose tolerance. When the vascular tissue of the mice was examined at dissection, there was also reduced atherosclerosis in the outlet of the aortic artery.
The results from the tests on human liver cells are complex but, in summary, both insulin and nobiletin reduced the secretion of VLDL.
How did the researchers interpret the results?
The researchers conclude that nobiletin could provide new insight into the treatment of lipid imbalance and atherosclerosis in people who are resistant to the action of insulin and are glucose intolerant.
This research investigated the effects of the flavanoid nobiletin when directly applied to human liver cells and fed to mice that were modified to have a condition similar to metabolic syndrome – a group of factors that increases the risk of cardiovascular disease and diabetes. Nobiletin was associated with a decrease in the production and secretion of bad fats in the liver cells, and the mice showed improved glucose tolerance and reduced atherosclerosis. These findings are worthy of further research.
It remains to be seen whether this chemical could be useful for people who are glucose intolerant or have conditions like the metabolic syndrome. Further research would need to assess how and why this substance works, whether the same effects would be seen if the chemical were consumed by humans, and how much of the substance would need to be consumed.
Although previous research has identified tangerines to be a source of the flavanoid nobiletin, tangerines were not actually involved in this current study.