A 1,000mg dose of the herb Salacia oblonga decreased insulin levels in healthy adults by 29 per cent and blood glucose levels by 23 per cent, report US researchers.
"These kinds of reductions are similar to what we might see with prescription oral medications for people with diabetes," said author Steve Hertzler, an assistant professor of nutrition at Ohio State University.
The study, published in the January issue of the Journal of the American Dietetic Association (vol 105, issue 1, pp65-71) was funded by the Ross Products Division of Abbott Laboratories. Hertzler is carrying out further work on the herb, native to regions of India and Sri Lanka, for the US company.
It is thought that Salacia oblonga acts in a similar way to diabetes medications by binding to intestinal enzymes called alpha-glucosidases, which are responsible for breaking down carbohydrates into glucose. When the enzyme binds to the herbal extract rather than a carbohydrate, less glucose gets into the blood stream, resulting in lowered blood glucose and insulin levels.
Plant extracts are increasingly being investigated by companies looking to market foods or supplements for people with diabetes or at risk of the condition.
The health ingredients unit at German group Degussa is currently waiting for results of a human trial on a new herbal extract, said to improve insulin sensitivity.
Pre-diabetes conditions are rising in parallel to the increasing incidence of obesity, now thought to affect more than 1 billion adults. An estimated 24 per cent of the US adult population has metabolic syndrome, a collection of risk factors for type 2 diabetes.
The Ohio researchers carried out four separate meal tolerance tests, spaced three to 14 days apart. The 39 participants were asked to drink 480ml of a beverage, which contained 0, 500, 700 or 1,000 milligrams of Salacia oblonga extract. Subjects fasted for at least 10 hours before consuming the drink.
The researchers took blood samples from each person every 15 to 30 minutes for three hours after consumption of the beverage to gauge blood glucose and insulin levels.
The beverage with the highest concentration of the herbal extract provided the most dramatic reduction in insulin and blood glucose levels - 29 per cent and 23 per cent lower, respectively, than in people on the control drink, which contained no herbal extract.
The other doses of the extract had no impact on blood glucose or insulin levels.
The researchers also found that the Salacia drinks caused an increase in breath hydrogen excretion, a measure of intestinal gas. But reports of gastrointestinal discomfort were minimal, Hertzler said.
"The increase in breath hydrogen excretion suggests a mechanism similar to prescription á-glucosidase inhibitors," write the authors.
The team is now studying what dose of the herb is most effective, and when it should be taken relative to a meal.
"We want to know how long it takes for the herb to bind to the enzymes that break down carbohydrates," Hertzler explained. "The participants in this study took the herb with their meal, but maybe taking it before eating would be even more effective."
The researchers are planning to study the extract's effects on diabetics.
"Lowering blood glucose levels lowers the risk of disease-related complications in people with diabetes," Hertzler said.
He added that poor compliance with diabetes medications often hinders their efficacy.
"It may be easier to get someone to take a herb with food or in a beverage, as opposed to a pill."
Dr Joerg Gruenwald, president of herbals consultancy Phytopharm, said the study "looks promising" but that he had not seen any salacia on the European market.