Corosolic acid is an active compound that was isolated from the leaves of a Southeast Asian tree commonly called banaba and scientifically known as Lagerstroemia speciosa. The leaves of this tree have been used by Filipinos to treat diabetes and kidney conditions.
Corosolic acid is also known as 2alpha-hydroxyursolic acid. Its structure is a pentacyclic titerpene, which means it contains five rings as can be seen in the illustration.
Corosolic acid was isolated from the banaba leaves using a methanol extract method, which produces two substances, the methanol fraction and the water fraction. The water fraction contained the corosolic acid, and this fraction was tested using a glucose uptake assay to determine if the substance had the anti-diabetic properties. The test showed that the water fraction, containing the corosolic acid, did exhibit an insulin-like activity.
However, what researchers found later, was that the methanol fraction also exhibited anti-diabetic activity. Since there is no corosolic acid in this fraction, there must be other active compounds in the banaba leaves.
Corosolic acid has been the topic of many research studies. Although there have been tests that concluded corosolic acid does have insulin-like activity, there are just as many studies that conclude that it does not. Patients taking supplements containing corosolic acid do report positive results. The question remains, if corosolic acid does possess anti-diabetic activity, what is the method of that activity?
There are dietary supplements on the market that contain corosolic acid. These supplements are marketed to aid in a variety of conditions, most of which revolve around insulin. Insulin is a hormone secreted by the pancreas. It is responsible for regulating the blood glucose (or sugar) level. Since there are studies that support the theories that corosolic acid has insulin-like properties, herbal supplement producers have created these products to promote those findings.