INSULIN SENSITIVITY INDEX, ACUTE INSULIN-RESPONSE, AND GLUCOSE EFFECTIVENESS IN A POPULATION-BASED SAMPLE OF 380 YOUNG HEALTHY CAUCASIANS -ANALYSIS OF THE IMPACT OF GENDER, BODY-FAT, PHYSICAL-FITNESS, AND LIFE-STYLE FACTORS

Background. Insulin sensitivity and insulin secretion are traits that are both genetically and environmentally determined. Aim. The aim of t his study was to describe the distribution of the insulin sensitivity index (Si), the acute insulin response, and glucose effectiveness (Sg) in young healthy Caucasians and to estimate the relative impact of an thropometric and environmental determinants on these variables. Method s. The material included 380 unrelated Caucasian subjects (18-32 yr) w ith measurement of Si, Sg and insulin secretion during a combined intr avenous glucose (0.3 grams/kg body weight) and tolbutamide (3 mg/kg bo dy weight) tolerance test. Results. The distributions of Si and acute insulin response were skewed to the right, whereas the distribution of Sg was Gaussian distributed. Sg was 15% higher in women compared with men (P < 0.001). Waist circumference, body mass index, maximal aerobi c capacity, and women's use of oral contraceptives were the most impor tant determinants of Si. Approximately one-third of the variation of S i could be explained by these factors. Compared with individuals in th e upper four-fifths of the distribution of Si, subjects with Si in the lowest fifth had higher waist circumference, higher blood pressure, l ower VO(2)max, and lower glucose tolerance and fasting dyslipidemia an d dysfibrinolysis. Only 10% of the variation in acute insulin response could be explained by measured determinants. Conclusion. Estimates of body fat, maximal aerobic capacity, and women's use of oral contracep tives explain about one-third of the variation in Si in a population-b ased sample of young healthy Caucasians.