Research done in India on normal-weight participants with normal blood glucose (or blood sugar) levels found that various doses of supplements containing green coffee extract all lowered blood sugar, with higher doses associated with larger drops.
"If this can influence a normal person's [glucose levels], then it should be even better for diabetics because they have a problem," said study author Joe Vinson, a professor of chemistry at the University of Scranton, in Pennsylvania. "The green coffee [extract] is the best aspect of coffee to be taken, I think."
Vinson was scheduled to present the research, done in India, on Tuesday at a meeting of the American Chemical Society in New Orleans. Studies presented at scientific conferences are typically not yet peer-reviewed and results are considered preliminary.
About 26 million Americans have type 2 diabetes, which is the most common form, according to the U.S. Centers for Disease Control and Prevention. Diabetes is linked to conditions including heart disease, blindness, kidney failure and lower-leg amputations.
A great deal of research has examined the potential health benefits of coffee. A much-touted 2012 study in the New England Journal of Medicine suggested that death rates fell with each additional cup consumed daily. Meanwhile, a 2009 Archives of Internal Medicine review of 18 studies involving more than 457,000 people indicated that each additional daily cup of coffee was associated with a 7 percent drop in the relative risk of developing type 2 diabetes.
The studies did not prove that coffee caused these health effects, but merely that an association existed.
Vinson's study analyzed 30 men and women of normal weight who did not have diabetes. They took supplements containing between 100 milligrams (mg) and 400 mg of the green coffee extract in a capsule with water, followed by glucose tolerance tests at several points afterward.
All doses of the extract appeared to lower participants' blood sugar levels, Vinson said, but a dose of 400 mg was associated with a 24 percent drop 30 minutes after taking the extract and a 31 percent drop 120 minutes later.
Vinson said he believes the sugar-lowering effects of green coffee extract are due to its concentration of chlorogenic acids -- antioxidants found in apples, cherries, plums and other fruits and vegetables. High temperatures used to roast coffee beans typically break down chlorogenic acids, he said, so coffee beverages contain less of them than extracts found in supplements.
"This study had strictly normal [participants], but it has a lot of potential for diabetes [control]," Vinson said. "It's a fairly cheap intervention and might cost less than a dollar or two per day -- less than a coffee at Starbucks."
But Dr. John Anderson, president of medicine and science at the American Diabetes Association, cautioned against reaching any firm conclusions from the research. Green coffee extract would need to be studied extensively before it could be offered as a potential prevention or remedy for diabetes, he said.
"To say that something can prevent or delay diabetes is almost impossible to prove unless they're willing to spend hundreds of millions of dollars on research. This needs rigorous scientific experiments to prove," Anderson said. "This is only  people, and all they did was look at a glucose tolerance test. I think it's interesting, but I don't think we really know any more than that."
The American Diabetes Association offers more facts about type 2 diabetes.