Long-term stability of low insulin responses to glucose in non-diabetic subjects

We investigated the stability of the insulin response to glucose in healthy subjects by making retrospective comparisons of insulin responses after two 60 min glucose infusion tests performed many years apart. The subjects (N = 49) were divided into two lower and two higher quartiles as assessed by the incremental 0-10 min insulin area during the initial glucose infusion test. Ages were initially 32.3 +/- 2.8 years in lower quartiles and 26.6 +/- 1.1 in higher quartiles and body mass indexes 21.6 +/- 0.6 kg/m2 and 21.8 +/- 0.5, respectively. The interval between the first and second glucose infusion tests was 8.1 +/- 2.8 years for lower quartiles and 10.4 +/- 1.3 for higher quartiles. In lower quartiles, the 0-10 min insulin area at first testing was 157.1 +/- 15.9 mU/l x 10 min and at follow-up 202.2 +/- 26.6 (+29%, NS). In higher quartiles, the insulin area decreased from 654.8 +/- 70.6 mU/l x 10 min at first testing to 489.8 +/- 53.6 at follow-up (-25%, p less than 0.05). The 0-60 min glucose area did not change significantly between glucose infusion tests in lower quartiles (+5%), but did increase by 12% (p less than 0.005) in higher quartiles. Only one subject of the lowest quartile at first testing changed to higher quartiles at follow-up. Predictable "regression toward the mean" at follow-up was moderate, hence the individual insulin response to glucose was relatively stable with time. This finding is compatible with the hypothesis that genetic factors are of major importance for the insulin response to glucose.