Insulin and cardiovascular diseases in Japanese work-site population with borderline to mild hypertension.

To clarify whether significant interrelations between hyperinsulinemia and cardiovascular diseases exist in Japanese, we analyzed serum insulin levels, fasting and after oral glucose load, in relation to blood pressure (BP), serum lipids, and incidence of acute myocardial infarction (MI) and stroke in 584 male employees of a railroad company with borderline to mild hypertension (age: 49 +/- 7 years, BP: 139 +/-13/90 +/- 8 mmHg, body mass index: BMI 24.0 +/- 2.8, mean +/- SD). Those who were taking antihypertensive drugs and/or hypoglycemic agents were excluded. The subjects were classified into five groups of comparable size according to sigma IRI (area composed by insulin levels at 0, 1, 2 hours post glucose load). Although averaged age, levels of fasting glucose and HbA1c were not significantly different among quintiles, the hyperinsulinemic groups had higher levels of fasting IRI and sigma glucose. Multiple regression analysis revealed that sigma IRI was associated positively with BMI, sigma glucose, systolic BP, total cholesterol, and negatively with HDL-cholesterol. During 7-year follow-up 7 cases with MI and 15 cases with stroke were registered. The subjects with MI, but not with stroke were involved in higher deciles of insulin levels. These results indicate that the insulin resistance syndrome exists in Japanese middle-aged men with borderline to mild hypertension. The association with cardiovascular morbid events appeared to be evident in coronary heart disease but not in cerebrovascular disease.