title: The bidirectional association between depressive symptoms and gait speed: evidence from the English Longitudinal Study of Ageing (ELSA).
abstract: BACKGROUND
  Depressive symptoms and physical performance are inversely associated, but it is unclear whether their association is bidirectional. We examined whether the association between depressive symptoms and physical performance measured using gait speed is bidirectional.
  
  
  METHODS
  We used a national sample of 4,581 community-dwelling people aged 60 years and older from the English Longitudinal Study of Ageing (from 2002-03 to 2008-09). We fitted Generalized Estimating Equation (GEE) regression models to analyse repeated measurements of gait speed (m/sec) and elevated depressive symptoms (defined as a score of ≥4 on the eight-item Center for Epidemiological Studies-Depression scale).
  
  
  RESULTS
  Slower gait speed was associated with elevated depressive symptoms both concurrently and two years later. After adjustment for previous depressive symptoms and sociodemographic, clinical, lifestyle, psychosocial, and cognitive factors the concurrent association was partially explained (Odds Ratio [OR] 0.42, 95% confidence interval [CI], 0.30 to 0.59, per 1m/sec increase in gait speed) and the two-year lagged association fully (OR 0.75, 95% CI, 0.56 to 1.00). Elevated depressive symptoms were associated with slower gait speed. Full adjustment for covariates (including previous gait speed) partially explained both the concurrent (β regression coefficient [β] -0.038, 95% CI, -0.050 to -0.026, for participants with elevated depressive symptoms compared with those with no or one symptom) and the two-year lagged associations (β -0.017, 95% CI, -0.030 to -0.005). Subthreshold depressive symptoms (defined as a score of two or three on the eight-item Center for Epidemiological Studies-Depression scale) were also associated with slower gait speed. Full adjustment for covariates partially explained both the concurrent (β -0.029, 95% CI, -0.039 to -0.019, for participants with subthreshold symptoms compared with those with no or one symptom) and the two-year lagged associations (β -0.011, 95% CI, -0.021 to -0.001).
  
  
  CONCLUSIONS
  The inverse association between gait speed and depressive symptoms appears to be bidirectional.
authors.affiliation: Department of Epidemiology and Public Health, University College London, London, United Kingdom. p.demakakos@ucl.ac.uk
authors.forename: Panayotes
authors.initials: P
authors.lastname: Demakakos
authors.forename: Rachel
authors.initials: R
authors.lastname: Cooper
authors.forename: Mark
authors.initials: M
authors.lastname: Hamer
authors.forename: Cesar
authors.initials: C
authors.lastname: de Oliveira
authors.forename: Rebecca
authors.initials: R
authors.lastname: Hardy
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Breeze
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology* / Q000523:psychology*; D003863:Depression; D005684:Gait; D006801:Humans; D008137:Longitudinal Studies; D008875:Middle Aged; D011569:Psychiatric Status Rating Scales; D012307:Risk Factors