Recent population changes in HbA1c and fasting insulin concentrations among US adults with preserved glucose homeostasis

Abstract

Although diagnosed type 2 diabetes has increased in the past decade, little is known about accompanying changes in fasting plasma glucose (FPG), HbA(1c) and fasting serum insulin (FI) levels in the non-diabetic population. Using population estimates from National Health and Nutrition Examination Surveys, we compared distribution of FPG, HbA(1c) and FI in non-diabetic US persons who were >or=20 years old in 1999 to 2006 with that in persons of the same age in 1988 to 1994. Age-, sex- and race-adjusted mean FPG levels between the two study periods did not change, but mean HbA(1c) and FI levels increased (0.10% and 4.8 pmol/l, respectively; p < 0.001 for both). The increased HbA(1c) level was driven largely by an upward shift in the lower end of the HbA(1c) distribution. In contrast, the increased FI level was driven primarily by an upward shift in the middle and higher end of FI distribution, especially among persons aged 20 to 44 years. After adjustments for BMI or waist circumference, the increase in the mean HbA(1c) level was attenuated (0.06%; p < 0.001), whereas the mean FPG level decreased by 0.1 mmol/l (p < 0.001) and the mean FI level no longer demonstrated significant change. Despite little change in the distribution of FPG levels, HbA(1c) and FI levels increased in the non-diabetic population in the past decade. The increase in FI levels suggests that levels of insulin resistance were greater among US adults, especially young adults, than in the previous decade.