Insulin and hypertension in the NHLBI Family Heart Study - A sibpair approach to a controversial issue

The association between insulin and hypertension remains equivocal. We ther efore investigated insulin levels in 3037 normotensive and 1067 hypertensiv e subjects from the National Heart, Lung and Blood Institute (NHLBI) Family Heart Study (FHS) by two different approaches. First, we compared insulin levels between normotensive and 275 untreated hypertensive subjects. Insuli n levels unadjusted as well as adjusted for age, sex, and center were signi ficantly higher in hypertensives. After adjustment for body mass index (BMI ), insulin remained significantly higher only in the diastolic hypertensive group (mean +/- SD 77.0 +/- 36.7 pmol/L, P < .01) but not in the isolated systolic hypertensive group (67.0 +/- 38.2 pmol/L) when compared to normote nsives (63.2 +/- 29.1 pmol/L). A sibpair analysis was then used that compar ed the intra-sibpair differences in insulin concentrations to the intra-sib pair differences in blood pressure (BP) levels. This approach was intended to control for the effects of genetic and residual shared environmental var iance upon insulin levels. The intra-sibpair difference in insulin concentr ations between concordant (diastolic and systolic Delta BP < 5 mm Hg) and d iscordant sibpairs (diastolic and systolic Delta BP > 15 and > 20 mm Hg, re spectively) was no longer significantly different when adjusted for BMI (2. 7 v 5.9 pmol/L for diastolic and -1.7 v -1.8 pmol/L for systolic BP). Even the random selection of one sibpair from each of the 326 families independe ntly of insulin and BP levels did not result in a significant correlation b etween the intra-sibpair differences in insulin and BP. Using an insulin re sistance index instead of insulin did not change our findings. Our investigation in the FHS sample of families suggests that there is only a small, if any, influence of insulin levels on BP after adjustment for ob esity-related sources of variation. Am J Hypertens 2000;13:240-250 (C) 2000 American Journal of Hypertension Ltd.