Banaba leaf extract (or corosolic acid) is typically found in supplements that help support healthy blood sugar levels and is claimed to stimulate glucose uptake and heighten insulin sensitivity.
Rats fed with 1% corosolic acid (glucosol) exhibited significantly reduced blood glucose after 90 minutes. Same formulation also exhibited significant and dose-dependent reduction in blood glucose (30% decrease after 2 weeks) over the range of 16-48 mg per day in 10 subjects with type II diabetes. A study in KK-Ay mice reported dose-dependent reduction in blood glucose levels 4 h after a single oral dose (2 mg/kg) which supported the hypotesis that corosolic acid improves glucose metabolism by reducing insulin resistance. A 12% decrease in fasting blood glucose was reported in 12 non-diabetic subjects who were given 10 mg of corosolic acid (as banaba extract standardized to 18% corosolic acid) for 2 weeks . In an unpublished study by Xu (mentioned in a review by Stohs et al. subjects received soft gel caps containing 10 mg of corosolic acid. Both fasting and 2h post-prandial blood glucose levels decreased by 10% compared to placebo group. In Fukushima et al. study 31 subjects were given 10 mg corosolic acid (99% pure) or placebo 5 minutes after 75 g of glucose tolerance test. It has been reported that corosolic acid reduced blood glucose levels from 60 to 120 minutes, with highest difference at 90 minutes.
In patients with type II diabetes mellitus intestinal cholesterol synthesis and cholesterol esterification is increased .Corosolic acid has been show to reduce cholesterol absorption process in the small intestine via inhibition of activity of cholesterol acyltransferase.
Mechanisms of Action
Corosolic acid is suggested to induce GLUT4 translocation. Translocation of more GLUT4 glucose transporters to the cell surface means increased insulin action. Disrupted GLUT4 gene has been shown to cause insulin resistance in skeletal muscles as well as diabetes .Corosolic acid also works as “insulin sensitizer” by inhibiting enzymatic activities of several diabetes-related non-receptor protein tyrosine phosphatases (such as PTP1B) which indirectly enhances insulin receptor B phosphorylation .Inhibition of protein tyrosine phosphatase 1B is an attractive target for treatment of diabetes and obesity . Corosolic acid also promotes glycolysis and suppresses gluconeogenesis.
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