title: Circadian activity rhythms and mortality: the study of osteoporotic fractures.
abstract: OBJECTIVE
  To determine whether circadian activity rhythms are associated with mortality in community-dwelling older women.
  
  
  METHODS
  Prospective study of mortality.
  
  
  METHODS
  A cohort study of health and aging.
  
  
  METHODS
  Three thousand twenty-seven community-dwelling women from the Study of Osteoporotic Fractures cohort (mean age 84).
  
  
  METHODS
  Activity data were collected using wrist actigraphy for a minimum of three 24-hour periods, and circadian activity rhythms were computed. Parameters of interest included height of activity peak (amplitude), midline estimating statistic of rhythm (mesor), strength of activity rhythm (robustness), and time of peak activity (acrophase). Vital status, with cause of death adjudicated through death certificates, was prospectively ascertained.
  
  
  RESULTS
  Over an average of 4.1 years of follow-up, there were 444 (14.7%) deaths. There was an inverse association between peak activity height and all-cause mortality rates, with higher mortality rates observed in the lowest activity quartile (hazard ratio (HR)=2.18, 95% confidence interval (CI)=1.63-2.92) than in the highest quartile after adjusting for age, clinic site, race, body mass index, cognitive function, exercise, instrumental activity of daily living impairments, depression, medications, alcohol, smoking, self-reported health status, married status, and comorbidities. A greater risk of mortality from all causes was observed for those in the lowest quartiles of mesor (HR=1.71, 95% CI=1.29-2.27) and rhythm robustness (HR=1.97, 95% CI=1.50-2.60) than for those in the highest quartiles. Greater mortality from cancer (HR=2.09, 95% CI=1.04-4.22) and stroke (HR=2.64, 95% CI=1.11-6.30) was observed for later peak activity (after 4:33 p.m.; >1.5 SD from mean) than for the mean peak range (2:50-4:33 p.m.).
  
  
  CONCLUSIONS
  Older women with weak circadian activity rhythms have higher mortality risk. If confirmed in other cohorts, studies will be needed to test whether interventions (e.g., physical activity, bright light exposure) that regulate circadian activity rhythms will improve health outcomes in older adults.
authors.affiliation: California Pacific Medical Center Research Institute, San Francisco Coordinating Center, UCSF, 185 Berry Street, Lobby 4, Suite 5700, San Francisco, CA 94107, USA. gtranah@psg.ucsf.edu
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Tranah
authors.forename: Terri
authors.initials: T
authors.lastname: Blackwell
authors.forename: Sonia
authors.initials: S
authors.lastname: Ancoli-Israel
authors.forename: Misti L
authors.initials: ML
authors.lastname: Paudel
authors.forename: Kristine E
authors.initials: KE
authors.lastname: Ensrud
authors.forename: Jane A
authors.initials: JA
authors.lastname: Cauley
authors.forename: Susan
authors.initials: S
authors.lastname: Redline
authors.forename: Teresa A
authors.initials: TA
authors.lastname: Hillier
authors.forename: Steven R
authors.initials: SR
authors.lastname: Cummings
authors.forename: Katie L
authors.initials: KL
authors.lastname: Stone
mesh_terms: D056044:Actigraphy; D000204:Activity Cycles; D000368:Aged; D000369:Aged, 80 and over; D002423:Cause of Death; D005260:Female; D005598:Fractures, Spontaneous / Q000453:epidemiology; D006801:Humans; D053208:Kaplan-Meier Estimate; D009026:Mortality; D010024:Osteoporosis / Q000453:epidemiology; D011446:Prospective Studies; D012307:Risk Factors; D014481:United States / Q000453:epidemiology