title: Association between Body Mass Index and Health-Related Quality of Life: The "Obesity Paradox" in 21,218 Adults of the Chinese General Population.
abstract: BACKGROUND
  There was no consistent recognition of the association between high or low body mass index (BMI) and health related quality of life (HRQL). The aim of this research was to study the association between BMI and HRQL in Chinese adults, and to further explore the stability of that association in the subgroup analysis stratified by status of chronic conditions.
  
  
  METHODS
  A total of 21,218 adults aged 18 and older were classified as underweight, normal weight, overweight, class I obese, and class II obese based on their BMI. HRQL was measured by the SF-36 Health Survey. The independent impact of each BMI category on HRQL was examined through standard least squares regression by comparing the difference of SF-36 scores and the minimum clinically important differences (MCID), which was defined as 3 points.
  
  
  RESULTS
  Compared to the normal weight, the class I obese was significantly associated with better HRQL scores in the mental component summary (MCS) (75.1 vs. 73.4, P<0.001). The underweight had the lowest score in both the physical components summary (PCS) (75.4 vs. 77.5, P<0.001) and mental components summary (MCS) (71.8 vs. 73.4, P<0.001). For the MCID, the HRQL score was reduced by more than 3 points in the physical functioning for the class II obese (D=-3.43) and the general health for the underweight (D=-3.71). Stratified analyses showed a similar result in the health subjects and chronic conditions, and it was significant in the chronic conditions.
  
  
  CONCLUSIONS
  The class I obese showed the best HRQL, especially in the mental domain. The worst HRQL was found in the underweight. The class II obese reduced HRQL in the physical functioning only. "Obesity paradox" was more obvious in the participants with chronic conditions.
authors.affiliation: School of Management, Beijing University of Chinese Medicine, Beijing, China.
authors.forename: Yanbo
authors.initials: Y
authors.lastname: Zhu
authors.affiliation: School of Preclinical Medicine, Beijing University of Chinese Medicine, Beijing, China.
authors.forename: Qi
authors.initials: Q
authors.lastname: Wang
authors.affiliation: Internal Medicine Department, Kaifeng Hospital of Traditional Chinese Medicine, Kaifeng, Henan, China.
authors.forename: Guoming
authors.initials: G
authors.lastname: Pang
authors.affiliation: Department of Quality Management, China-Japan Friendship Hospital, Beijing, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Lin
authors.affiliation: Division of Biostatistics and Clinical Epidemiology, School of Medicine, University of Toyama, Toyama, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Origasa
authors.affiliation: School of Management, Beijing University of Chinese Medicine, Beijing, China.
authors.forename: Yangyang
authors.initials: Y
authors.lastname: Wang
authors.affiliation: School of Management, Beijing University of Chinese Medicine, Beijing, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Di
authors.affiliation: Department of Clinical Nutrition, China-Japan Friendship Hospital, Beijing, China.
authors.forename: Mai
authors.initials: M
authors.lastname: Shi
authors.affiliation: School of Preclinical Medicine, Beijing University of Chinese Medicine, Beijing, China.
authors.forename: Chunpok
authors.initials: C
authors.lastname: Fan
authors.affiliation: School of Management, Beijing University of Chinese Medicine, Beijing, China.
authors.forename: Huimei
authors.initials: H
authors.lastname: Shi
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015992:Body Mass Index; D002681:China / Q000453:epidemiology; D005260:Female; D006304:Health Status; D006306:Health Surveys; D006801:Humans; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000453:epidemiology*; D050177:Overweight / Q000453:epidemiology; D011788:Quality of Life; D013851:Thinness / Q000453:epidemiology; D055815:Young Adult