Comparing Measures of Obesity in Relation to Health Care Use in Adults from the Canadian Longitudinal Study on Aging

Abstract

Background: Obesity has been associated with increased health care use, but it is unclear whether this is consistent across all measures of obesity. The objectives of this thesis were to compare obesity defined by four anthropometric measures, body mass index (BMI), waist circumference (WC), waist-to-hip ratio (WHR), and percent body fat (%BF), and to estimate their associations with health care use among Canadian adults. Methods: A secondary data analysis was conducted from 30,097 individuals aged 45-85 years from the Canadian Longitudinal Study on Aging. Anthropometric measures were collected by trained research assistants and %BF, the reference standard, was measured using dual-energy x-ray absorptiometry. Obesity was defined as BMI≥30.0 kg/m2, WC≥88cm for females and ≥102cm for males, WHR≥0.85 for females and ≥0.90 for males, and %BF>35% for females and >25% for males. Approximately 18 months after baseline data collection, self-reported health care use in the past 12 months was collected, including any contact with a general practitioner, medical specialist, emergency department, and being a patient in a hospital overnight. Pearson correlation coefficients and sensitivity and specificity analyses were conducted to compare anthropometric measures to %BF. Relative risks and risk differences were calculated for measures of health care use, adjusted for sex, age, education, income, urban/rural, marital status, smoking status, and alcohol use. Secondary analyses were also stratified by sex and age. Results: The prevalence of obesity defined by BMI was 29%, by WC was 42%, by WHR was 62%, and by %BF was 73%. BMI and WC were highly correlated with %BF (r=0.75 and r=0.70, respectively) and WHR was weakly correlated with %BF (r=0.29). BMI and WC cut points demonstrated high specificity (>93%) and lower sensitivity (<58%) in predicting obesity defined by %BF. WHR cut points demonstrated high sensitivity (95%) and lower specificity (28%) in males, but lower sensitivity (44%) and high specificity (83%) in females in predicting %BF- defined obesity. There was an increased relative and absolute risk of health care use for all measures of obesity and all health care services. For example, WC-defined obesity was associated with increased relative risk (RR) of hospital overnight stay (RR: 1.40, 95% CI: 1.28- 1.54) and the risk difference (per 100) was 2.6 (95% CI:1.9-3.3). The risk of health care use was similar amongst females and males with obesity although relative risks and risk differences attenuated in the oldest adult group aged 75 and older compared to the youngest group aged 45- 54. Conclusion: The prevalence of obesity among Canadian adults varied substantially by anthropometric measure. BMI and WC have stronger correlations and concordance with %BF than does WHR, however all measures were positively associated with increased health care use. Further research should be conducted on obesity cut points to discern the best measure to predict health care use.