Feeding diabetic rats the tea was also associated with lower production of the sugar alcohol sorbitol from glucose, report the researchers in the Journal of Agricultural and Food Chemistry. A build-up of sorbitol is linked to damage in the eyes or of nerve cells.
“The results [of this new study] clearly suggested that daily consumption of chamomile tea with meals could contribute to the prevention of the progress of hyperglycemia and diabetic complications,” wrote the researchers from the University of Toyama in Japan and the Institute of Grassland and Environmental Research in Aberystwyth, UK.
If the results can be repeated in other animal studies, and in future human studies, it may see chamomile (Matricaria chamomilla L.) tea added to the ever-growing list of dietary approaches for the prevention and/or management of diabetes.
Indeed, Dr Victoria King, research manager at British charity Diabetes UK, cautioned: "This study was carried out on rats with diabetes during a 21-day period. More research would be needed before we can come to any firm conclusions about the role chamomile tea plays in fighting diabetes-related complications.
"Diabetes UK wouldn't recommend people with diabetes increase their chamomile tea intake just yet.”
An estimated 19 million 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 26 million by 2030.
In the US, there are almost 24 million people with diabetes, equal to seven per cent of the population. The total costs are thought to be as much as $174 billion, with $116 billion being direct costs from medical expenditures, according to 2007 American Diabetes Association figures.
The researchers, led by Atsushi Kato, investigated the effect of supplemental chamomile tea and its major components (umbelliferone, herniarin, esculetin, isoscopoletin, apigenin, luteolin, quercetin, R-bisabolol, and R-farnesene) to prevent or improve diabetic complications.
Studies using rat cells and human red blood cells were performed, while an additional feeding study was performed with rats. Kato and co-workers report that the full hot water extract, as well as esculetin and quercetin possessed moderate inhibitory activity of sucrase enzymes, which are responsible for the conversion of sucrose to fructose and glucose. Inhibition would reduce the rise in glucose levels.
Moreover, inhibition of the enzyme aldose reductase (ALR2), which converts glucose to sorbitol, was also observed when red blood cells were incubated with the hot water extract and some of the components.
“It has already been reported that the activity of erythrocytes ALR2 increases in diabetic patients and erythrocytes sorbitol levels in rats are positively correlated with the levels in the lens, sciatic nerve, and retina,” wrote Kato. Such a build-up can produce damage and complications.
The researchers reported a 75, 79, 74, and 68 per cent inhibition of ALR2 for umbelliferone, esculetin, luteolin, and quercetin when the compounds were used at a concentration of 200 micromoles.
A 21-day feeding study used rats that had received an intravenous injection of streptozotocin to induce diabetes. Supplementing the diets of the animals with chamomile tea or its extracts was found to influence blood glucose levels. Specifically, the tea and quercetin were found to suppress blood glucose levels in the animals.
“In conclusion, the present study demonstrated that daily consumption of chamomile tea with meals could be potentially useful in the prevention and self-medication of hyperglycemia and diabetic complications,” wrote the researchers.
Commenting independently on the results, Dr King said that more research was needed to substantiate a potential role for chamomile tea in diabetes prevention and management.
"Eating a healthy balanced diet, taking regular physical activity and adhering to any prescribed medicines remain key ways to effectively control blood glucose levels, blood pressure and blood fats. Good diabetes management will help reduce the risk of serious complications such as heart disease, stroke and blindness," she added.
Source: Journal of Agricultural and Food ChemistryVolume 56, Pages 8206-8211“Protective Effects of Dietary Chamomile Tea on Diabetic Complications”Authors: A. Kato, Y. Minoshima, J. Yamamoto, I. Adachi, A.A. Watson, R.J. Nash