The review of 16 clinical trials of 15 herbal formulas the herbs showed reduced levels of blood sugar in people with “prediabetes,” which are those with impaired glucose control can become type 2 diabetes.

When the researchers gathered data from eight of these studies found that adding an herbal remedy to lifestyle changes doubled the likelihood of normalizing the blood sugar levels.

Moreover, people who had used the remedies were two thirds less likely to develop diabetes during the study, which lasted about 9 months.

The findings are published in the Cochrane Library, Cochrane Collaboration, an international organization that evaluates medical research.

For authors, the results are “quite promising.” But they cautioned that the studies had some methodological biases, preventing firm conclusions.

“There are many herbal remedies on the shelves, but few were subjected to a rigorous test,” he told Reuters Health via e-mail the author of the study, Suzanne J. Grant, Center for Complementary Medicine Research at the University of Western Sydney in Australia.

Many of the trials analyzed, explained, were “high risk of bias” that might overestimate the effects of therapies.

So, he added, is more rigorous trials necessary before recommending the use of herbal medicines to prevent diabetes.

The studies included a total of 1391 men and women with impaired glucose tolerance or blood fasting glucose, which are problems of control of blood sugar that increase plasma levels, but not enough to diagnose diabetes .

The studies examined various mixtures of Chinese herbs traditionally used to control blood sugar, as Jiangtang Bushen, Kang Tang Xiaoke huaya and yin.

In most trials, the products were added to lifestyle changes and compared with the effects of these changes only, which were not detailed in most studies.

Grant said that if the prediabetic want to try an herbal product, they must first consult with the physician and, ideally, be used with the supervision of a specialist in herbal medicine.