Prevalence of insulin resistance in essential hypertension

To establish the prevalence of insulin resistance in hypertensive subjects.

The euglycaemic hyperinsulinaemic clamp was performed in 420 hypertensive patients taking no antihypertensive medication and in 51 age- and sex-matched healthy controls. No subjects with known diabetes mellitus or fasting hyperglycaemia were included in the study.

The mean value for insulin-mediated glucose uptake (M-value at clamp) in the healthy control group (8.2 mg/kg per min) -2 SD was chosen as the cutoff limit for insulin resistance (4.4 mg/kg per min). At this cutoff limit, 27% of the hypertensive subjects were insulin resistant (mean value 3.1 mg/kg per min in this group, range 0.7-4.3). A similar prevalence of insulin resistance in hypertensive patients was found (31%) if the 95th percentile of the non-normally distributed insulin sensitivity index (M/I at clamp) was used to define the cutoff limit for insulin resistance: (4.4 mg/kg per min)/(mU/l x 100). In the insulin-resistant group, 50% showed elevated levels of serum triglycerides (> 2.0 mmol/l), 50% had abdominal obesity (waist:hip ratio > 0.95), 20% had elevated levels of serum uric acid (> 400 mumol/l) and 48% had low high-density lipid (HDL)-cholesterol levels (< 1.0 mmol/l). Half of the insulin-resistant hypertensives but only 20% of the non-insulin resistant group had two or more of these other four metabolic impairments (P < 0.001). Insulin resistance in hypertension was also associated with an increased heart rate (+3 beats/min faster than in non-insulin resistant hypertensive patients, P < 0.01), but no significant differences in blood pressure were found between insulin resistant and non-insulin resistant hypertensive patients.

When insulin resistance was defined as an M-value at clamp of < 4.4 mg/kg per min, based on calculations from a healthy control sample, about 25% of a sample of hypertensive subjects, taking no antihypertensive treatment and with no history of diabetes mellitus or hyperglycaemia, was found to be insulin resistant. This group of insulin-resistant hypertensives also displayed a high degree of clustering of other metabolic impairments.