Is insulin or its precursor independently associated with hypertension? An epidemiological study in Japanese-Brazilians

Japanese individuals living outside Japan are more susceptible to chronic diseases included in the insulin resistance syndrome. Hyperinsulinemia and hypertension are associated, but large studies adjusting for confounders are still required. The present evaluated if insulin (I) or proinsulin (PI) was associated with hypertension after adjustment for other risk factors, in first (n=238) and second (n=292) generation Japanese-Brazilians, aged 40 to 79 years, living in a developed city in Brazil. Blood pressure (BP) was measured by random-zero sphygmomanometry. People with mean systolic/diastolic BP >140/90 mm Hg or taking antihypertensive drugs were considered hypertensive. Diagnosis of diabetes was based on results of an oral glucose tolerance test using WHO criteria. I and PI after fasting and 2 hours after glucose load were determined by specific immunofluorimetric assays. The first generation was older than the second (65.6+/-9.2 versus 53.6+/-8.4 years, P<.01) and male/female ratios were 1.14 and 0.87, respectively. The age-adjusted prevalence of hypertension was 29.2% with no difference between sexes or generations. Higher body mass index (25.2+/-4.3 versus 23.8+/-3.3 kg/m(2)), waist-to-hip ratio (0.939+/-0.067 versus 0.919+/-0.073), plasma glucose (6.3+/-2.3 versus 5.6+/-1.8 mmol/L), cholesterol (5.74+/-1.19 versus 5.48+/-1.08 mmol/L), and creatinine (74+/-26 versus 83+/-36 mu mol/L) were found among the hypertensives (P<.05). Univariate analyses showed associations of obesity, diabetes, and dyslipidemia with hypertension. Logistic regression analyses demonstrated that 2-hour I (OR, 1.22; 95% CI, 1.02 to 1.46) and fasting PI (OR, 1.14; 95% CI, 1.00 to 1.31) remained significantly associated with hypertension, after adjustment for age, sex, generation, family history of hypertension, smoking habits, waist-to-hip ratio, serum creatinine, glucose intolerance, and dyslipidemia. Japanese-Brazilians have a higher prevalence of hypertension than the general population in Brazil. High levels of 2-hour I, seen in hypertensives, may be interpreted as independent risk factors for hypertension in this population. Our findings suggest that fasting PI should be useful, in addition to insulin, to assess risk factors for hypertension in epidemiological studies.