The Correlation Between Body Mass Index and Health-Related Quality of Life: Data from Two Weight Loss Intervention Studies.

ABSTRACT

INTRODUCTION: The correlation between body mass index (BMI) and utility in participants with obesity was assessed using health-related quality-of-life data collected in two weight loss intervention studies, SCALE and STEP 1. METHODS: Short Form Health Survey 36-Item (SF-36) scores from SCALE and STEP 1 were mapped to EuroQoL-5 dimensions-3 levels (EQ-5D-3L) using an established algorithm to derive utilities for the UK. SF-36 scores from STEP 1 were converted into Short Form 6 dimension (SF-6D) utilities for Portugal using the tool developed by the University of Sheffield. The correlation between baseline BMI and utility was assessed by multiple linear regression analyses, controlling for demographic and clinical parameters. RESULTS: A higher baseline BMI correlated with lower EQ-5D-3L and SF-6D utilities, although the trend was non-significant. Assuming linearity between BMI ranges 30-40 kg/m2, an additional unit of BMI correlated with 0.0041 and 0.0031 lower EQ-5D-3L scores in SCALE and 0.0039 and 0.0047 lower EQ-5D-3L and 0.0027 and 0.0020 lower SF-6D scores in STEP 1 for men and women, respectively. CONCLUSION: In individuals with comparable demographic characteristics and weight-related comorbidities, a 1 unit change in BMI leads to a difference of up to 0.005 in utility indices. TRIAL REGISTRATION ClinicalTrials.gov identifiers SCALE (NCT01272219) and STEP 1 (NCT03548935).

Cost-effectiveness analyses compare health benefits and costs between treatments to inform decisions on healthcare resource allocation. Health benefits are typically quantified as quality-adjusted life-years (QALYs) gained. The calculation of QALYs relies on health-related quality-of-life (HRQoL) data, which are collected from participants. However, to allow comparisons across multiple interventions and diseases, HRQoL needs to be converted into a standardized, generic measure, i.e., a utility index ranging from 0 (equivalent to death) to 1 (perfect health). In this study, HRQoL data from the SCALE and STEP 1 clinical trials were converted into utility indexes and analyzed against participants' weight at study start, expressed as body mass index (BMI, kg/m2). Our study indicates that there is a negative correlation between BMI and health utility at a population level whereby an additional unit of BMI, within the range of 30­40 kg/m2, was consistently correlated with an up to 0.005 worsening in the utility index across men and women. The estimated effect size was small, indicating that BMI alone may not explain the differences in participants' HRQoL and general population evaluation of these.