High blood pressure and insulin resistance: influence of ethnic background

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Abstract
Hyperinsulinaemia links non-insulin dependent diabetes (NIDDM), obesity, and hypertension, each an insulin-resistant state in its own right. Insulin resistance predicts the occurrence of NIDDM, and plays a major role in its pathogenesis. We tested the hypothesis that hyperinsulinaemia may also predict hypertension in a sample (n= 2905) of the mixed population of San Antonio, in which hyperinsulinaemia and NIDDM are more prevalent among Mexican-Americans than non-Hispanic whites. Whilst in the whole sample the hypertensives had significantly (P < 0.001) higher plasma insulin concentrations than the normotensives, high blood pressure was significantly (P < 0.01) more frequent among non-Hispanic whites than Mexican-Americans regardless of diabetes status. After adjusting for factors (age, sex, body mass, and body fat distribution) known to affect insulin levels, a direct relationship between post-glucose plasma insulin concentrations and prevalence of hypertension was still present in both ethnic groups. In Mexican-Americans, however, the standardized prevalence of hypertension was significantly (P < 0.001) lower at any given insulin concentration. Post-glucose plasma glucose levels also were directly related to hypertension prevalence in both groups; again, the regression line was shifted downward and, furthermore, less steep (P < 0.02) in Mexican-Americans, suggesting relative protection against the negative effect of hyperglycaemia on blood pressure. Dyslipidaemia (higher total cholesterol and triglyceride, and lower HDL-cholesterol concentrations) was strongly associated with hyperinsulinaemia and blood pressure in both ethnic groups. After adjusting for plasma insulin, only hypertriglyceridaemia was associated with high blood pressure, with no inter-ethnic difference. We conclude that in this population hyperinsulinaemia is characteristic of hypertension but does not explain its prevalence against a divergent ethnic background. Other factors that determine high blood pressure must interact with insulin resistance to determine the prevalence rate of hypertension in the population.