title: Changes in relative fitness and frailty across the adult lifespan: evidence from the Canadian National Population Health Survey.
abstract: BACKGROUND
  The prevalence of frailty increases with age in older adults, but frailty is largely unreported for younger adults, where its associated risk is less clear. Furthermore, less is known about how frailty changes over time among younger adults. We estimated the prevalence and outcomes of frailty, in relation to accumulation of deficits, across the adult lifespan.
  
  
  METHODS
  We analyzed data for community-dwelling respondents (age 15-102 years at baseline) to the longitudinal component of the National Population Health Survey, with seven two-year cycles, beginning 1994-1995. The outcomes were death, use of health services and change in health status, measured in terms of a Frailty Index constructed from 42 self-reported health variables.
  
  
  RESULTS
  The sample consisted of 14,713 respondents (54.2% women). Vital status was known for more than 99% of the respondents. The prevalence of frailty increased with age, from 2.0% (95% confidence interval [CI] 1.7%-2.4%) among those younger than 30 years to 22.4% (95% CI 19.0%-25.8%) for those older than age 65, including 43.7% (95% CI 37.1%-50.8%) for those 85 and older. At all ages, the 160-month mortality rate was lower among relatively fit people than among those who were frail (e.g., 2% v. 16% at age 40; 42% v. 83% at age 75 or older). These relatively fit people tended to remain relatively fit over time. Relative to all other groups, a greater proportion of the most frail people used health services at baseline (28.3%, 95% CI 21.5%-35.5%) and at each follow-up cycle (26.7%, 95% CI 15.4%-28.0%).
  
  
  CONCLUSIONS
  Deficits accumulated with age across the adult spectrum. At all ages, a higher Frailty Index was associated with higher mortality and greater use of health care services. At younger ages, recovery to the relatively fittest state was common, but the chance of complete recovery declined with age.
authors.affiliation: Division of Geriatric Medicine, Department of Medicine, Dalhousie University, Halifax, NS. kenneth.rockwood@dal.ca
authors.forename: Kenneth
authors.initials: K
authors.lastname: Rockwood
authors.forename: Xiaowei
authors.initials: X
authors.lastname: Song
authors.forename: Arnold
authors.initials: A
authors.lastname: Mitnitski
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D002170:Canada / Q000453:epidemiology; D016009:Chi-Square Distribution; D005260:Female; D016330:Frail Elderly / Q000706:statistics & numerical data*; D006304:Health Status; D006306:Health Surveys; D006801:Humans; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D010809:Physical Fitness; D015995:Prevalence; D016016:Proportional Hazards Models; D012737:Sex Factors; D055815:Young Adult