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Dietary flavonoids could provide health benefits for patients with type 2 diabetes

Diabetes Care; ‘Chronic ingestion of flavon-3-ols and isoflavones improves insulin sensitivity and lipoprotein status and attenuates estimated 10-year CVD risk in medicated postmenopausal women with type 2 diabetes: a one year double-blind randomized controlled trial’; Photo: Michael Cannon/Flickr

Mon, 16 Jan 2012

Diets high in flavonoids may reduce the risk of heart disease for women with type 2 diabetes, according to a new study by the University of East Anglia.

Published today in the journal Diabetes Care, the findings of the 12-month trial provide further evidence that diet offers extra protection to those at high risk of cardiovascular events. The results also suggest that regular consumption of flavonoid-rich foods can help in the management of diabetes itself.

Diabetes is an increasing global problem, with recent research suggesting that complications of the disease account for 7 per cent of all deaths and 12 per cent of healthcare costs.

Flavonoids occur in foods such as berries, tea and chocolate, though the researchers have emphasised that the results do not mean that women with type 2 diabetes should eat more chocolate. This is because commercially available chocolate does not contain nearly as much of it as the women in this trial consumed, and eating too much chocolate may adversely affect weight unless the diet is balanced for total energy intake.

Ninety-three postmenopausal women with type 2 diabetes took part in the trial. The age of participants ranged from 51 to 74 years. Half were given two small bars of flavonoid-enriched chocolate each day and half were given placebo chocolate bars. Those receiving the extra flavonoids reduced their risk of suffering a heart attack in the next decade by 3.4 per cent - an important effect for a dietary intervention. Their insulin resistance and cholesterol levels were significantly reduced by the flavonoids.

"These results are significant from a public health perspective because they provide further concrete evidence that diet has a beneficial clinical effect over and above conventional drug treatment," said lead researcher Prof Aedin Cassidy of the Department of Nutrition, Norwich Medical School at UEA.

Flavonoids are bioactive constituents which occur naturally in various foods and drinks including tea, red wine, many fruits and vegetables, and dark chocolate. The chocolate bars used in the trial were specially formulated with the help of a Belgian chocolatier to provide a high dose of two flavonoid sub-classes - flavan-3-ols which are found in cocoa and tea, and isoflavones which are found in soy.

Prof Cassidy said she was not advocating eating more commercially available chocolate because many commercial chocolates do not contain high levels of the beneficial flavonoids.

Postmenopausal women with diabetes were chosen for the study because, despite being on established statin therapy, they are a very high risk group for heart disease. Deaths due to heart disease increase rapidly after the menopause and having type 2 diabetes increases this risk by a further three-and-a-half times.

Previous studies have shown that dietary flavonoids reduce the risk factors for heart disease in healthy people. However, this is the first long-term study to examine their effect on a medicated, high risk group.

Funded by Diabetes UK, the study was led by UEA in collaboration with colleagues at the Elsie Bertram Diabetes Centre, Norfolk and Norwich University Hospital (NNUH) and the Institute of Food Research (IFR).

Dr Ketan Dhatariya, one of the researchers and a consultant in diabetes at the Norfolk and Norwich University Hospital, said: "This is an important result. We are not saying that people with diabetes should be eating lots of chocolate, but that foods that are rich in flavonoids can potentially reduce the risk of heart attacks and strokes, which sadly remain the leading causes of premature death in this group of women."

Dr Iain Frame, director of research at Diabetes UK, said: "This trial assessed the effects of flavonoids on the risk of heart disease in post-menopausal women with type 2 diabetes over a period of one year. Although it involved quite a small number of women already at high risk of heart disease, these compounds appeared to offer them better protection against heart problems than conventional drugs when administered under very carefully controlled circumstances.

"Flavonoids are found in tea, red wine and other foods, but this study only looked at the effects of specially prepared chocolate with much higher amounts of flavonoids than in chocolate available commercially. We would be very concerned if the results of this research were reported as encouraging people with type 2 diabetes to increase their consumption of chocolate and red wine. Both of these can cause weight gain that would eliminate the health benefits described here and should only be consumed as part of a healthy balanced diet. It will be interesting to see whether larger studies of different flavonoids in more diverse populations over longer periods demonstrate similar effects."

Further research is now needed to determine the relative influence of the two flavonoid sub-classes featured in this study, and to examine whether similar effects are observed in male patients with type 2 diabetes or in other patient groups.

'Chronic ingestion of flavon-3-ols and isoflavones improves insulin sensitivity and lipoprotein status and attenuates estimated 10-year CVD risk in medicated postmenopausal women with type 2 diabetes: a one year double-blind randomized controlled trial' by P Curtis (UEA), M Sampson (NNUH), J Potter (UEA), K Dhatariya (NNUH), P Kroon (IFR) and A Cassidy (UEA) is published online by Diabetes Care on January 16 2012.

Photo: Michael Cannon/Flickr