The aim of the study was to investigate the effect of metformin on insulin secretion and insulin resistance in hyperinsulinaemic normal glucose tolerant people with metabolic syndrome who represent a high-risk group for development of type 2 diabetes mellitus and cardiovascular disease. Fifty two participants of mean age 40.1±14.2 yrs were included in an open-label prospective one year observational clinical study in which plasma glucose, serum insulin during a 3-h oral glucose tolerance test, Glucose/Insulin ratio (G/I), Quantitative Insulin Sensitivity Check Index (QUICKI) and Homeostasis Model Assessment of Insulin Resistance (HOMA-IR) at three months intervals following metformin treatment were evaluated. The results showed that fasting serum insulin, 3-h post glucose load (PGL) serum insulin and HOMA-IR significantly reduced at 6, 9 month and at 1 year. Fasting plasma glucose, 1-h and 2-h PGL serum insulin significantly decreased at 3, 6, 9 month and at 1 year. Fasting G/I significantly increased at 9 month and at 1 year. 1-h G/I and QUICKI significantly increased at 3, 6, 9 month and at 1 year. 2-h and 3-h G/I significantly increased at 6, 9 month and at 1 year of metformin treatment (all p<0.001). In conclusion, metformin restores physiological insulin secretion and reduces insulin resistance in hyperinsulinaemic normal glucose tolerant people with metabolic syndrome and could be considered as a therapeutic option for prevention of type 2 diabetes mellitus and cardiovascular disease.
 

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