Impaired Glucose Tolerance (IGT) is an abnormal metabolic state following glucose metabolic steady state but prior to diabetes. IGT is an important stage during the progression of diabetes, with an underlying mechanism of insulin resistance and pancreatic β cell dysfunction. IGT is one of the diseases that shows significant beneficial response to acupuncture treatment. Original findings from the investigators'laboratory show that transcutaneous auricular vagus nerve stimulation (taVNS) which is innervated by vagus nerve, would enhance the activity of pancreatic β cells, promote the secretion of insulin, upregulate the expression of insulin receptors in central as well as peripheral tissues, thus to improve glycometabolism. In this study, the investigators would further illuminate the mechanism of taVNS at "yidan-pi" auricular acupoints on the regulation of glucose metabolism, its improvement of the IGT state in rat model, as well as its regulation effect on insulin receptor expression and insulin resistance, and systematically illustrate the clinical effective of this treatment on IGT, with emphasize on its influence on the concentrations of glucose and HbA1c, and thus provide an effective proposal for clinical acupuncture.

Inclusion Criteria:

• ages between 20 and 70
• fasting plasma-glucose(FPG) less than 7 mmol/L, or 2h p-glucose 7.8-11.1 mmol/L
• anti-diabetic medication of any kind
• able to provide informed consent

Exclusion Criteria:

• comorbidities that would prohibit participation in study procedures, including cardiovascular disease, hematological system disease or psychosis
• females of childbearing potential who were pregnant, breast-feeding
• infection within the 1 month
• known or suspected abuse of alcohol or narcotics