Variation by body mass index and age in waist-to-hip ratio associations with glycemic status in an aboriginal population at risk for type 2 diabetes in British Columbia, Canada

Background: It is unclear whether obesity and age modify or confound relations between abdominal adiposity and metabolic risk factors for type 2 diabetes. ObJective: Our objective was assess the consistency of relations between abdominal adiposity and glycemic variables across discrete categories of obesity and age. Design: We performed a stratified analysis of prevalence data from a rural screening initiative in British Columbia, Canada. Subjects were Salishan Indians, all healthy relatives of individuals with type 2 diabetes [n = 151; age: 18-80 y; body mass index (BMI, in kg/m²): 17.0- 48.2]. We measured waist-to-hip ratio (WHR) (2 categories); insulin, glycated hemoglobin (Hb A(1c)), and 2-h glucose concentrations (2 categories); and BMI (4 categories). BMI and age-specific odds ratios (ORs) and 95% CIs were calculated. Results: WHR-glycemic variable relations were not consistent across BMI and age strata. Risks associated with high WHR were: for persons with BMIs from 25 to 29, elevated insulin (OR: 6.71; 95% CI: 1.41, 34.11) and Hb A(1c) (OR: 16.23; 95% CI: 2.04, 101.73) concentrations; for persons aged 18-34 y, elevated insulin concentrations [OR: indeterminate (⁺∞); 95% CI: 1.89, ⁺∞]; and, for persons aged 35-49 y, elevated Hb A(1c) (OR: ⁺∞; 95% CI: 3.17, ⁺∞) and 2-h glucose (OR: 9.15; 95% CI: 1.74, 59.91) concentrations. Conclusions: WHR discriminates risk of type 2 diabetes in overweight but not obese individuals. Abdominal adiposity is associated with elevated insulin concentrations in younger age groups and with impaired glucose control in middle-aged groups, suggesting metabolic staging by age on a continuum from insulin resistance to impaired glucose tolerance.