A glucose-lowering effect similar to metformin was observed in vitro for berberine; however, no effect was seen on insulin secretion (Yin et al 2002).
Similarly, fasting blood glucose, total cholesterol and triglyceride levels significantly decreased after 8 weeks of treatment with 187.5 or 562.5 mg/kg of berberine Goldenseal 633 in an experimental model of glucose intolerance (Leng et al 2004). In an additional in
vitro study using insulin secreted from pancreatic cells, incubated with berberine for 12 hours, the authors concluded that berberine increased insulin production. The relationship of these trials to oral doses in humans is unknown.
Blood glucose, blood lipids, muscle triglycerides and insulin sensitivity were measured before and after the ingestion of berberine or metformin in rats fed a high-fat diet (Gao et al 1997). In this trial berberine and metformin improved insulin resistance and liver glycogen levels, but had no effect on blood glucose, insulin, lipid and muscle triglyceride levels. The study was able to demonstrate that berberine was as effective as metformin for improving insulin sensitivity in the rats.
Berberine inhibits alpha-glucosidase and therefore reduces the transport of glucose through the intestinal epithelium (Pan et al 2003).
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