title: Impact of metabolic comorbidity on the association between body mass index and health-related quality of life: a Scotland-wide cross-sectional study of 5,608 participants.
abstract: BACKGROUND
  The prevalence of obesity is rising in Scotland and globally. Overall, obesity is associated with increased morbidity, mortality and reduced health-related quality of life. Studies suggest that "healthy obesity" (obesity without metabolic comorbidity) may not be associated with morbidity or mortality. Its impact on health-related quality of life is unknown.
  
  
  METHODS
  We extracted data from the Scottish Health Survey on self-reported health-related quality of life, body mass index (BMI), demographic information and comorbidity. SF-12 responses were converted into an overall health utility score. Linear regression analyses were used to explore the association between BMI and health utility, stratified by the presence or absence of metabolic comorbidity (diabetes, hypertension, hypercholesterolemia or cardiovascular disease), and adjusted for potential confounders (age, sex and deprivation quintile).
  
  
  RESULTS
  Of the 5,608 individuals, 3,744 (66.8%) were either overweight or obese and 921 (16.4%) had metabolic comorbidity. There was an inverted U-shaped relationship whereby health utility was highest among overweight individuals and fell with increasing BMI. There was a significant interaction with metabolic comorbidity (p = 0.007). Individuals with metabolic comorbidty had lower utility scores and a steeper decline in utility with increasing BMI (morbidly obese, adjusted coefficient: -0.064, 95% CI -0.115, -0.012, p = 0.015 for metabolic comorbidity versus -0.042, 95% CI -0.067, -0.018, p = 0.001 for no metabolic comorbidity).
  
  
  CONCLUSIONS
  The adverse impact of obesity on health-related quality of life is greater among individuals with metabolic comorbidity. However, increased BMI is associated with reduced health-related quality of life even in the absence of metabolic comorbidity, casting doubt on the notion of "healthy obesity".
authors.affiliation: Institute for Health and Wellbeing, University of Glasgow, Glasgow G12 8RZ, UK.
authors.forename: Zia
authors.initials: Z
authors.lastname: Ul-Haq
authors.forename: Daniel F
authors.initials: DF
authors.lastname: Mackay
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Fenwick
authors.forename: Jill P
authors.initials: JP
authors.lastname: Pell
mesh_terms: D000328:Adult; D000368:Aged; D015992:Body Mass Index; D015897:Comorbidity; D003430:Cross-Sectional Studies; D005260:Female; D006304:Health Status; D006306:Health Surveys; D006801:Humans; D008297:Male; D008659:Metabolic Diseases / Q000453:epidemiology* / Q000503:physiopathology; D008875:Middle Aged; D009765:Obesity / Q000453:epidemiology* / Q000503:physiopathology; D011788:Quality of Life; D012606:Scotland