Researchers found the herbs could work in much the same way as prescription anti-diabetic medication.
In the new study published in American Chemical Society's Journal of Agricultural and Food Chemistry, researchers found that how the herbs are grown makes a difference, and they also identified which compounds contribute the most to this promising trait.
Recent research has shown that herbs could provide a natural way to help lower glucose in blood. So Elvira Gonzalez de Mejia at the University of Illinois at Urbana-Champaign and colleagues decided to take a closer look.
They tested four different herbs, either greenhouse-grown or dried commercial versions, for their ability to interfere with a diabetes-related enzyme, which is also a target of a prescription drug for the disease.
They found that greenhouse herbs contained more polyphenols and flavonoids compared to the equivalent commercial herbs.
But this didn't affect the concentration required to inhibit the enzyme.
Commercial extracts of Greek oregano, Mexican oregano and rosemary were better inhibitors of the enzyme, required to reduce risk of type-2 diabetes, than greenhouse-grown herbs.
The researchers said more studies are needed to understand the role of these compounds in reducing the risk of type-2 diabetes in humans.