Banaba (Lagerstroemia speciosa L.) extracts have been used for many years in
folk medicine to treat diabetes, with the first published research study being reported in 1940. This review summarizes the current literature regarding banaba and its constituents. The
hypoglycemic effects of banaba have been attributed to both
corosolic acid as well as
ellagitannins. Studies have been conducted in various animal models, human subjects and in vitro systems using water soluble banaba leaf extracts,
corosolic acid-standardized extracts, and purified
corosolic acid and
ellagitannins. Pure
corosolic acid has been reported to decrease
blood sugar levels within 60 min in human subjects.
Corosolic acid also exhibits
antihyperlipidemic,
antioxidant, antiinflammatory, antifungal,
antiviral,
antineoplastic and osteoblastic activities. The beneficial effects of banaba and
corosolic acid with respect to various aspects of
glucose and lipid metabolism appear to involve multiple mechanisms, including enhanced cellular uptake of
glucose, impaired hydrolysis of
sucrose and starches, decreased gluconeogenesis and the regulation of lipid metabolism. These effects may be mediated by
PPAR, MAP K, NF-κB and other signal transduction factors. No adverse effects have been observed or reported in animal studies or controlled human clinical trials. Banaba extract,
corosolic acid and other constituents may be beneficial in addressing the symptoms associated with
metabolic syndrome, as well as offering other health benefits.