Objectives: Although it is well known that obesity is closely related to insulin resistance, the incidence of the development of insulin resistance in people with obesity is not known. In this study, we investigated the incidence of insulin resistance in citizens of two rural communities in Japan.
Subjects and methods: The subjects were 102 men and 126 women over the age of 30 years selected from 1035 citizens who had undergone medical examinations in the towns of Tanno and Sobetsu, Hokkaido, in 1991 and 1998. Those who were on medication for hypertension, diabetes, hyperlipidaemia, coronary heart disease and cerebral vessel disease were excluded. The simple index to determine insulin resistance [i.e. homeostasis model assessment (HOMA-R) > or = 1.73] was used, and subjects who were determined to be positive for insulin resistance according to this index in 1991 were also excluded in order to determine the incidence of insulin resistance in subjects who had no abnormalities other than obesity. The systolic blood pressure (SBP), diastolic blood pressure, body mass index (BMI), triglyceride level, high-density lipoprotein level, blood sugar level, serum insulin value and HOMA-R were measured in all subjects in 1991 and in 1998. Moreover, the subjects were divided into two groups according to BMI, a normal group consisting of subjects with BMI < 25 and an obesity group consisting of subjects with BMI > or = 25. We also compared the incidences of insulin resistance in normal and obesity groups of subjects who were newly determined to be positive for insulin resistance on the basis of data obtained from medical examinations conducted in 1998.
Results: The incidence of insulin resistance was significantly higher in the obesity group than in the normal group (25.0 vs. 4.5%). The results of logistic regression analysis showed that obesity was closely related to insulin resistance and that the relative risk of development of insulin resistance adjusted for age, sex, SBP, FPG and HDL was 3.193 (95% CI 1.085-9.401).
Conclusions: The incidence of insulin resistance was significantly higher in the obesity group than in the normal group in this study, suggesting that improvement in obesity is important for prevention of the occurrence of type 2 diabetes or atherosclerotic disease based on insulin resistance.