title: Comorbidity and functional trajectories from midlife to old age: the Health and Retirement Study.
abstract: BACKGROUND
  The number of diseases and physical functioning difficulties tend to increase with age. The aim of this study was to examine the trajectories of physical functioning across age groups and whether the trajectories differ according to disease status in different population subgroups.
  
  
  METHODS
  Repeat data from a nationally representative population sample, the Health and Retirement Study, was used. Participants were 10,709 men and 13,477 women aged 60-107 years at baseline with biennial surveys from 1992 to 2010. Average length of follow-up was 10.3 years ranging from 0 to 18 years. Disease status and physical functioning was asked about at all study phases and 10 items were summed to obtain a physical functioning score (0-10).
  
  
  RESULTS
  Age modified the relationship between number of chronic diseases and physical functioning with older participants having more physical functioning difficulties with increasing number of diseases. An average 70-year-old participant with no diseases had 0.89 (95% CI: 0.85-0.93) physical functioning difficulties, with one disease 1.72 (95% CI: 1.69-1.76) difficulties, with two diseases 2.57 (95% CI: 2.52-2.62) difficulties, and with three or more diseases 3.82 (95% CI: 3.76-3.88) difficulties. Of the individual diseases memory-related diseases, stroke, pulmonary diseases, and arthritis were associated with significantly higher physical functioning difficulties compared with other diseases.
  
  
  CONCLUSIONS
  Comorbidity is associated with greater burden of physical functioning difficulties. Of the studied diseases, memory-related diseases, stroke, pulmonary diseases, and arthritis alone or in combination limit most physical functioning.
authors: Department of Public Health, University of Turku, Turku, Finland. Department of Health, Functional Capacity and Welfare, National Institute for Health and Welfare (THL), Helsinki, Finland. sari.stenholm@utu.fi.
authors: Sari
authors: S
authors: Stenholm
authors: Stress Research Institute, Stockholm University, Stockholm, Sweden.
authors: Hugo
authors: H
authors: Westerlund
authors: Department of Epidemiology and Public Health, University College London, London.
authors: Jenny
authors: J
authors: Head
authors: Stress Research Institute, Stockholm University, Stockholm, Sweden.
authors: Martin
authors: M
authors: Hyde
authors: Department of Society, Human Development, and Health, Harvard School of Public Health, Boston, Massachusetts.
authors: Ichiro
authors: I
authors: Kawachi
authors: Centre of Expertise for the Development of Work and Organizations, Finnish Institute of Occupational Health, Helsinki and Turku, Finland.
authors: Jaana
authors: J
authors: Pentti
authors: Department of Epidemiology and Public Health, University College London, London. Centre of Expertise for the Development of Work and Organizations, Finnish Institute of Occupational Health, Helsinki and Turku, Finland.
authors: Mika
authors: M
authors: Kivimäki
authors: Department of Public Health, University of Turku, Turku, Finland. Centre of Expertise for the Development of Work and Organizations, Finnish Institute of Occupational Health, Helsinki and Turku, Finland. Turku University Hospital, Turku, Finland.
authors: Jussi
authors: J
authors: Vahtera
mesh_terms: D000203:Activities of Daily Living; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D002908:Chronic Disease / Q000453:epidemiology*; D015897:Comorbidity; D005260:Female; D006304:Health Status; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D012179:Retirement; D012959:Socioeconomic Factors; D014481:United States
keywords: Aging; Comorbidity; Disability.; Physical functioning