In this study, we investigated preventive effects of black tea on obesity and hyperglycemia in C57BL/6 mice fed a high-fat diet for 14 weeks. During the feeding period, mice were given the following black teas: BT1 containing 3,000 mg/L total catechins and 864 mg/L caffeine; and BT2 containing 1,437 mg/L total catechins and 594 mg/L caffeine. Both BT1 and BT2 suppressed high-fat diet-caused body weight gain, deposition of white adipose tissue, and increases in plasma lipids and glucose. Moreover, both BT1 and BT2 counteracted the high-fat diet-caused decrease in the expression of insulin receptor (IR)-β and glucose transporter 4 (GLUT4), markers for insulin resistance. Of these effects, BT2 were stronger than that of BT1. In conclusion, black tea prevents hyperglycemia and insulin resistance through maintenance of IR-β and GLUT4 expression in high-fat diet-fed mice, with an appropriate concentration of tea producing maximal effectiveness.

To investigate the effect of catechins on Cu dynamics in mice, the body hair of mice administered with or without green tea extract was subjected to neutron activation analysis at a research reactor. Neutron activation analysis revealed that green tea extract might have the ability to promote excretion of Cu from the body to the hair.