Diagnosis was made based on diagnostic criteria for diabetes mellitus suggested by American Diabetes Association in 2009 and accepted later by International Diabetes Federation and World Health Organization in 2011: (1) fasting plasma glucose ≥ 126 mg / dL (7 mmol / L), (2) 2-h plasma glucose ≥ 200 mg / dl (11.1 mmol / l) during an oral glucose tolerance test, (3) HbA1c ≥ 6.5%.