NEW YORK (Reuters Health) - A number of traditional Chinese herbs may help control blood sugar levels in people at high risk of diabetes, a new research review suggests.

The review, which examined 16 clinical trials of 15 different herbal formulations, found that the herbs generally helped lower blood sugar levels in people with "pre-diabetes" -- those with impaired blood-sugar control that can progress to full-blown type 2 diabetes.

When the researchers pooled data from eight of the studies, they found that adding an herbal remedy to lifestyle changes doubled the likelihood of participants' blood sugar levels returning to normal.

What's more, people using the remedies were two-thirds less likely to progress to diabetes during the studies, which ran for an average of nine months.

The findings appear in the Cochrane Library, which is published by the Cochrane Collaboration, an international organization that evaluates medical research.

The results, say the researchers, are "quite promising." However, they also stress that the studies had shortcomings in their methods that make it hard to draw firm conclusions.

"There are a lot of herbal medicine products on the shelves, but few have been subjected to a rigorous trial," lead researcher Suzanne J. Grant, of the Center for Complementary Medicine Research at the University of Western Sydney, in Australia, told Reuters Health in an email.

Many of the trials her team examined, she explained, had a "high risk of bias" that can overestimate the effects of the treatments.

The gold standard for proving a treatment's efficacy is a clinical trial where participants are randomly assigned to receive either the real treatment or a placebo, with both the researchers and participants unaware of who is taking the real drug.

Grant's team found that those processes were often absent or not clearly detailed in the trials they reviewed.

So, she said, there is still a need for more rigorous trials before any herbal product can be recommended for diabetes prevention.

The studies included a total of 1,391 men and women with either impaired glucose tolerance or impaired fasting glucose -- problems in blood-sugar control that lead to sugar levels that are elevated, but not high enough to diagnose diabetes.

The studies tested various Chinese herbal mixes traditionally used for blood-sugar control -- products like Jiangtang Bushen, Xiaoke huaya and Tang Kang yin.

In most trials, the products were added to lifestyle changes and tested against the effects of lifestyle changes alone -- though the specific changes were not detailed in most reports.

Grant suggested that if people with pre-diabetes do want to try an herbal product, they first consult their doctor and, ideally, take any herbs under a guidance of a health provider qualified in herbal medicine.

She pointed out that in traditional Chinese medicine, herbs are recommended based on individuals' unique situations, and not as a one-size-fits-all prescription.

As far as safety, the review found no serious side effects attributed to the herbal products. However, Grant noted, like all medicines, herbs have the potential for unexpected side effects or interactions with other drugs.

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SOURCE: Cochrane Library, online October 7, 2009.