title: Cognitive and physical functions as determinants of delayed age at onset and progression of disability.
abstract: BACKGROUND
  This study examined the association of cognitive and physical functions with age-related transition and progression of activities of daily living (ADL) disability in a population-based longitudinal cohort of nondisabled older adults.
  
  
  METHODS
  A longitudinal population-based cohort study of 5,317 initially nondisabled older adults with an average age of 73.6 years of an urban Chicago community were interviewed annually for up to 8 years from 2000 through 2008. Cognitive function was assessed using a standardized global cognitive score and physical function using a combination of measured walk, tandem stand, and chair stand. A novel two-part model was used to access the relationship between cognitive and physical functions and age at onset and progression of ADL disability.
  
  
  RESULTS
  The sample consisted of 5,317 participants, 65% blacks, and 61% females. Twenty-five percent reported an onset of ADL disability during follow-up. After adjusting for confounders, lower cognitive and physical functions were associated with an increased risk for lower age at onset. Lower cognitive function was longitudinally associated with increased rate of progression of disability after onset. However, lower physical function did not alter the rate of progression of ADL disability.
  
  
  CONCLUSIONS
  Cognitive and physical functions were associated with age at onset. However, only cognitive function was associated with the rate of progression of ADL disability.
authors.affiliation: Rush Institute for Healthy Aging, Department of Internal Medicine, Rush University Medical Center, 1645 W Jackson Blvd, Suite 675, Chicago, IL 60612, USA. kumar_rajan@rush.edu
authors.forename: Kumar B
authors.initials: KB
authors.lastname: Rajan
authors.forename: Liesi E
authors.initials: LE
authors.lastname: Hebert
authors.forename: Paul
authors.initials: P
authors.lastname: Scherr
authors.forename: Xinqi
authors.initials: X
authors.lastname: Dong
authors.forename: Robert S
authors.initials: RS
authors.lastname: Wilson
authors.forename: Denis A
authors.initials: DA
authors.lastname: Evans
authors.forename: Carlos F
authors.initials: CF
authors.lastname: Mendes de Leon
mesh_terms: D000203:Activities of Daily Living; D017668:Age of Onset; D000368:Aged; D000369:Aged, 80 and over; D003071:Cognition; D003072:Cognition Disorders / Q000453:epidemiology; D015986:Confounding Factors, Epidemiologic; D004185:Disability Evaluation; D006233:Persons with Disabilities; D018450:Disease Progression; D005260:Female; D015577:Geriatric Assessment; D006801:Humans; D008297:Male