A single trial of holy basil reported a benefit in controlling fasting blood glucose only. G sylvestre was used in a number of studies, again with generally beneficial results. Gymnema was also a constituent in 2 of the formulas that reported beneficial results: D-400 and Ayush-82.
Methodological shortcomings. The evidence we found falls short of proof. As noted, the individual studies we assessed had significant methodological shortcomings. Few used a randomized, placebo-controlled design, despite the feasibility of such methods. Studies generally were underpowered to determine even large effect sizes. Many studies involved an extremely small number of subjects (fewer than 10). A number of studies failed to use appropriate statistical methods in reporting the results. Furthermore, the duration of most studies was short, and only intermediate outcomes (measure of blood sugar control) were reported. Longer term studies that assess clinical outcomes are required. Lastly, there is great heterogeneity in the available literature on Ayurvedic treatment for diabetes, despite the fact that the overwhelming majority of studies test herbal therapy. Heterogeneity exists in the herbs and formulas tested and in the method of their preparation.
No true studies of Ayurveda. None of the identified studies assessed Ayurveda as a system of diagnosis and care. The literature reported mainly studies of single herbs; however, in clinical Ayurvedic practice, herbs are usually given in combination. Formulas can include minerals and metals in addition to multiple plants.
Ayurvedic practitioners assert that the sum of a formula is more potent than the constituents taken individually and, further, that the mineral and metal components boost the formula’s potency. Additional Ayurvedic therapies such as diet, yoga, or special purification routines, should be controlled for when recruiting and assessing patients. It is unclear, perhaps doubtful, that taking a single component of Ayurvedic is sufficient to represent the holistic effect of Ayurvedic interventions.
Limitations of our review. Our searches showed that herbal therapies were emphasized in published studies of Ayurveda. However, no conclusions can be drawn about the use of Ayurveda as a whole system for the treatment of diabetes. Although extensive efforts were made to obtain the relevant literature from India, studies not published in English were excluded, as were MD thesis reports. A handful of studies could not be obtained. Therefore we may not have included in this review all clinical trials. By specifically hand searching documents published in India, we identified that an important body of Ayurvedic literature is not identifiable using traditional systematic review methods.
In summary, we found preliminary evidence suggesting that some herbs and herbal formulas used in Ayurvedic therapy can have clinically important glucose-lowering effects. C indica, holy basil, and Gymnema are particularly worthy of additional study.
Acknowledgments
This research was performed by the Southern California Evidence-Based Practice Center based at RAND, Santa Monica, CA under contract with the Agency for Healthcare Research and Quality (Contract No. 290-97-0001) with support from the National Center for Complementary and Alternative Medicine. The authors of this article are responsible for its contents. No statement in this article should be construed as an official position of the Agency for Healthcare Research and Quality, the National Center for Complementary and Alternative Medicine, National Institutes of Health, or the US Department of Health and Human Services.
CORRESPONDING AUTHOR
Paul G. Shekelle, MD, PhD, West Los Angeles VA Medical Center, 111G, 11301 Wilshire Blvd, Los Angeles, CA 90073. E-mail: shekelle@rand.org. At the time of this study, Dr. Shekelle was a Senior Research Associate of the Veterans Affairs Health Services Research and Development Service.