title: Association between objectively measured sleep quality and physical function among community-dwelling oldest old Japanese: A cross-sectional study.
abstract: OBJECTIVE
  The present study examined the association between objective measures of sleep quality and performance-based measures of physical function in community-dwelling oldest old Japanese.
  
  
  METHODS
  This cross-sectional study included 207 community-dwelling adults aged 80 years or older (92 men, 115 women; age 83.5 ± 2.6 years [range 80-95 years]). Participants wore an accelerometer (ActiGraph GT3X+) on their non-dominant wrist for 24 h per day over seven consecutive nights. Sleep parameters included total sleep time, sleep efficiency and wake after sleep onset during the night for a week. Performance-based physical function measures were handgrip strength, knee extension strength, and usual and maximum walking speeds. Multivariable linear regression was carried out to determine the associations between weekly sleep parameter averages and physical function measures.
  
  
  RESULTS
  Approximately 24% of participants had a total sleep time of less than 6 h a night, and 13% had greater than 8 h a night. Overall, average daily physical activity was 1771.8 ± 520.6 (counts/min/day). In multiple linear regression, sleep efficiency and wake after sleep onset were significantly associated with maximum walking speed (β = 0.277; 95% confidence interval [CI] 0.103 to 0.351 and β = -0.214; 95% CI -0.339 to -0.082, respectively) and usual walking speed (β = 0.200, 95% CI 0.035 to 0.305 and β = -0.174; 95% CI -0.341 to -0.064, respectively), after adjusting for potential confounding factors including daily physical activity. Both sleep qualities were also independently associated with knee extension strength. However, wake after sleep onset was not associated with handgrip strength.
  
  
  CONCLUSIONS
  Objectively measured sleep quality was associated with physical function in the oldest old. Further research is required to identify the temporality of associations between sleep and physical function.
authors.affiliation: Research Team for Promoting Independence of the Elderly, Tokyo Metropolitan Institute of Gerontology, Tokyo, Japan.
authors.forename: Miji
authors.initials: M
authors.lastname: Kim
authors.affiliation: Research Team for Promoting Independence of the Elderly, Tokyo Metropolitan Institute of Gerontology, Tokyo, Japan.
authors.forename: Hideyo
authors.initials: H
authors.lastname: Yoshida
authors.affiliation: Japan Society for the Promotion of Science, Tokyo, Japan.|Faculty of Medicine, University of Tsukuba, Ibaraki, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Sasai
authors.affiliation: Research Team for Promoting Independence of the Elderly, Tokyo Metropolitan Institute of Gerontology, Tokyo, Japan.
authors.forename: Narumi
authors.initials: N
authors.lastname: Kojima
authors.affiliation: Research Team for Promoting Independence of the Elderly, Tokyo Metropolitan Institute of Gerontology, Tokyo, Japan.
authors.forename: Hunkyung
authors.initials: H
authors.lastname: Kim
mesh_terms: D000203:Activities of Daily Living; D000369:Aged, 80 and over; D016001:Confidence Intervals; D003430:Cross-Sectional Studies; D005260:Female; D016330:Frail Elderly; D006801:Humans; D057187:Independent Living; D007564:Japan; D008297:Male; D016017:Odds Ratio; D010809:Physical Fitness / Q000502:physiology*; D012111:Residence Characteristics; D012890:Sleep / Q000502:physiology*; D012893:Sleep Wake Disorders / Q000175:diagnosis / Q000453:epidemiology*; D018709:Statistics, Nonparametric; D013997:Time Factors; D014041:Tokyo
keywords: accelerometer; oldest old; physical activity; physical function; sleep