Longitudinal association between body mass index and health-related quality of life

Abstract

Objective: Health-related quality of life (HRQoL) is an important outcome in individuals with a high risk for cardiovascular diseases. We investigated the association of HRQoL and body mass index (BMI) as an indicator for obesity.

Design: Secondary longitudinal analysis of the ORBITAL study, an intervention study which included high-risk cardiovascular primary care patients with hypercholesterolemia and an indication for statin therapy.

Methods: HRQoL was determined with the generic Short Form (SF)-12 health status instrument. Body weight and height were assessed at baseline and at months 6, 12, 18, 24, 30, and 36. We used a linear and a linear mixed-effects regression model to investigate the association between BMI and SF-12 summary scores at baseline as well as between change in BMI and SF-12 summary scores over 3 years. We adjusted for age, sex, smoking status, and in the longitudinal analysis also for the study arm and its interaction term with time.

Results: Of the 7640 participants who completed the baseline questionnaire, 6726 participants (mean age: 61 years) were analyzed. The baseline BMI was inversely associated with physical and mental SF-12 summary scores (β [95% CI] per 1 kg/m2: -0.36 [-0.41; -0.30] and -0.05 [-0.11; -0.00], respectively). A significant association between the change in BMI and physical SF-12 summary scores over time was only present in women (-0.18 [-0.27; -0.09]) and only in obese participants (-0.19 [-0.29; -0.10]). A change in BMI was directly associated with mental SF-12 summary scores (0.12 [0.06; 0.19]) in the total population.

Conclusion: Increases in BMI were associated with decreases in physical HRQoL, particularly in obese individuals and in women. In contrast, the mental HRQoL seemed to increase with increasing BMI over time. Thus, body weight management with respect to the HRQoL should be evaluated differentially by sex and body weight status.

Trial registration: ClinicalTrials.gov NCT00379249.

Figure 1. Participant flow from randomization in the ORBITAL intervention study to analyses of the present study.

Abbreviations: BMI = body mass index, CABG = coronary artery bypass graft, HRQoL = health-related quality of life, ORBITAL = Open Label Primary Care Study Rosuvastatin Based Compliance Initiatives to Achievements of LDL Goals, PCI = percutaneous coronary intervention.

Figure 2. Bland Altman plot for baseline BMI calculated from the self-reported and physician-reported body weight.

The bias (mean) between the two methods is marked by the full line (–), the upper and lower limits of agreement (mean ±2 standard deviations) by the dotted line (···) and the regression line by the broken line (− − −). Six observations are outside the axis range. Abbreviation: BMI = body mass index.

Figure 3. Mean changes in the physical (part A) and mental (part B) SF-12 summary scores from baseline to 36-month follow-up according to baseline BMI category in three weight-change groups.

Weight-change groups: weight loser (BMI change over 36 months <−0.5 kg/m²), stable weight (BMI change −0.5 to 0.5 kg/m²), and weight gainer (BMI change >0.5 kg/m²). Abbreviations: BMI = body mass index in kg/m², SF = Short Form.