The review included 44 randomized clinical trials with more than 3,000 participants using six herbal remedies: apple cider vinegar, cinnamon, curcumin, fenugreek seeds, ginger, and saffron.
Apple cider vinegar, fenugreek seeds, curcumin (turmeric), and cinnamon resulted in statistically significant reductions in fasting blood glucose, compared with the control groups in the clinical trials. Out of all the remedies, the authors found apple cider vinegar to be the most effective for lowering fasting blood glucose levels.
The review also found that apple cider vinegar and fenugreek seeds had a statistically significant effect on reducing A1c, compared with the control groups. The authors found the herbal remedies made no difference to insulin level or homeostatic model assessment for insulin resistance (HOMA-IR).
The results are published online in Diabetes & Metabolic Syndrome: Clinical Research & Reviews. The authors said they hoped the review would help medical professionals and people with type 2 diabetes understand the effectiveness of different herbal remedies and consider incorporating these remedies into standard care.
“Some people use curcumin, some use ginger, some use apple cider [vinegar], but it’s not clear which is better,” said Shiv Mudgal, PhD, corresponding author of the paper and an associate professor in nursing at the All India Institute of Medical Sciences in Deoghar, India.
“We thought it would be nice to get some idea about how they work and how they compete with each other,” said Subodh Kumar, MD, the first author and an associate professor in pharmacology at the All India Institute of Medical Sciences in Deoghar, India.
They wanted to understand how the herbal remedies worked by including insulin level and HOMA-IR as measurable outcomes but found nothing conclusive. Instead, they speculated that the effect of apple cider vinegar and fenugreek seeds on blood glucose and A1c could be related to delayed gastric emptying, among other mechanisms.
However, the results should be interpreted with caution, said Dr. Kumar.
Apple cider vinegar had three clinical trials to back the finding, and fenugreek seeds had four studies supporting the results – fewer than the other included remedies. The authors also identified risks of bias from the randomization process and the allocation concealment process in several of the included trials.
Most of the studies included only short follow-up periods, meaning that the long-term effects of using these herbal remedies to help manage type 2 diabetes remain unclear.
The six herbal remedies included in the study were chosen out of dozens of popular complementary medicines for the strength and number of clinical trials backing their use.
The limited number included in the review is a drawback, according to Merlin Willcox, DPhil, a clinical lecturer in general practice at the University of Southampton, England, who was not involved in the research.
“It means they’ve left out stuff that’s potentially effective,” Dr. Willcox said in an interview.
Dr. Willcox, who has coauthored a review of herbal remedies for glycemic control in type 2 diabetes, said he was surprised that apple cider vinegar came out on top in this analysis.
His review concluded that aloe vera leaf gel, psyllium fiber, and fenugreek seeds appeared to be the most effective at reducing A1c, compared with the control groups of the included trials, out of 18 plant-based remedies.
There were no adverse effects associated with the herbal remedies, according to Dr. Mudgal. However, the evidence for the herbal remedies included in their review also lacked substantial follow-up periods assessing their long-term effects.
“You need to look at the evidence for each individual remedy; it’s not just about what plant it is, but it’s about what preparation, what dose. All of that comes into play,” Dr. Willcox said.
Up to 3.6 million people use herbal remedies to manage type 2 diabetes in the United States, according to a 2014 study cited by the review authors. The number is much higher elsewhere: As many as two-thirds of patients with diabetes in India and Saudi Arabia incorporate herbal remedies to help manage symptoms, whereas about half of patients with diabetes in the United Kingdom use herbal medicines.
Experts warn of the risks associated with using herbal medicines to complement traditional therapies.
“I caution my patients about dietary supplements and herbals because of the lack of high-quality data demonstrating efficacy and safety,” Katherine H. Saunders, MD, DABOM, cofounder of Intellihealth and clinical assistant professor of medicine at Weill Cornell Medicine, New York, said in an interview.
For Dr. Willcox, the risks relate to where patients get their information from. Many patients with type 2 diabetes are too scared to talk to their doctor about herbal medicines.
“They think their doctor is going to be negative or dismissive,” Dr. Willcox said. “So patients are getting their information from family and friends or from the Internet, which is not necessarily the most reliable, evidence-based source of information.”
The authors have reported no relevant financial relationships.
A version of this article appeared on Medscape.com.