Kobori of the National Agriculture and Food Research Organization, Ibaraki, Japan, investigated the effect of quercetin on the improvement of the diabetic symptoms . They conducted experiments on streptozotocin-induced diabetic rats to determine the effect of quercetin on liver injury. Quercetin was fed for two weeks, after which hepatic gene expression was measured using a DNA microarray. Quercetin administration lowered the streptozotocin-induced increase in blood glucose levels and improved plasma insulin levels. A diet with 0.5% quercetin suppressed streptozotocin-induced alteration of gene expression.
A study by Chao and co-workers at Taoyuan General Hospital, Taiwan., demonstrated the protective effect of quercetin and its glucuronide and sulfate metabolites against glucose induced of human endothelial cells . The researchers found that the quercetin metabolites inhibited in a dose-dependently manner the glucose-induced apoptosis. The quercetin metabolites inhibited Jun N-terminal kinase and caspase-3 and reduced intracellular H2O2 level. They concluded that quercetin may have a pharmacological application in treating cardiovascular disease in diabetes mellitus patients.
Winged Spindle is used in China as a folk medicine to treat type 2 diabetes. This herb is rich in kaempferol and quercetin. Scientists from the Chinese Pharmaceutical University investigated the possible mechanism of antidiabetic activity of these phytochemicals in cultured adipocytes . They concluded that "kaempferol and quercetin potentially act at multiple targets to ameliorate hyperglycemia, including by acting as partial agonists of glitazone receptor".
 Dietary quercetin alleviates diabetic symptoms and reduces streptozotocin-induced disturbance of hepatic gene expression in mice. Mol Nutr Food Res. 2009 Jul;53(7):859-68.
 The antioxidant effects of quercetin metabolites on the prevention of high glucose-induced apoptosis of human umbilical vein endothelial cells. Br J Nutr. 2009 Apr;101(8):1165-70.
 Kaempferol and quercetin isolated from Euonymus alatus improve glucose uptake of 3T3-L1 cells without adipogenesis activity. Life Sci. 2008 Mar 12;82(11-12):615-22.