title: Low 25-hydroxyvitamin D predicts the onset of mobility limitation and disability in community-dwelling older adults: the Health ABC Study.
abstract: BACKGROUND
  Although low 25-hydroxyvitamin D (25(OH)D) is prevalent among older adults and is associated with poor physical function, longitudinal studies examining vitamin D status and physical function are lacking. We examined the association between 25(OH)D, parathyroid hormone (PTH), and the onset of mobility limitation and disability over 6 years of follow-up in community-dwelling, initially well-functioning older adults participating in the Health, Aging and Body Composition study (n = 2,099).
  
  
  METHODS
  Serum 25(OH)D and PTH were measured at the 12-month follow-up visit (1998-1999). Mobility limitation and disability (any/severe difficulty walking 1/4 mile or climbing 10 steps) was assessed semiannually over 6 years of follow-up. The association between 25(OH)D, PTH, and mobility limitation and disability was examined using Cox proportional hazard regression models adjusted for demographics, season, behavioral characteristics, and chronic conditions.
  
  
  RESULTS
  At baseline, 28.9% of the participants had 25(OH)D <50 nmol/L and 36.1% had 25(OH)D of 50 to <75 nmol/L. Participants with 25(OH)D <50 and 50 to <75 nmol/L were at greater risk of developing mobility limitation (HR (95% CI): 1.29 (1.04-1.61) and 1.27 (1.05-1.53), respectively) and mobility disability (HR (95% CI): 1.93 (1.32-2.81) and 1.30 (0.92-1.83), respectively) over 6 years of follow-up compared with participants with 25(OH)D ≥75 nmol/L. Elevated PTH, however, was not significantly associated with developing mobility limitation or disability.
  
  
  CONCLUSIONS
  Low 25(OH)D was associated with an increased risk of mobility limitation and disability in community-dwelling, initially well-functioning black and white older adults. Prevention or treatment of low 25(OH)D may provide a pathway for reducing the burden of mobility disability in older adults.
authors.affiliation: Department of Internal Medicine, Wake Forest School of Medicine, Winston-Salem, North Carolina 27157-1207, USA. dhouston@wakehealth.edu
authors.forename: Denise K
authors.initials: DK
authors.lastname: Houston
authors.forename: Rebecca H
authors.initials: RH
authors.lastname: Neiberg
authors.forename: Janet A
authors.initials: JA
authors.lastname: Tooze
authors.forename: Dorothy B
authors.initials: DB
authors.lastname: Hausman
authors.forename: Mary Ann
authors.initials: MA
authors.lastname: Johnson
authors.forename: Jane A
authors.initials: JA
authors.lastname: Cauley
authors.forename: Doug C
authors.initials: DC
authors.lastname: Bauer
authors.forename: M Kyla
authors.initials: MK
authors.lastname: Shea
authors.forename: Gary G
authors.initials: GG
authors.lastname: Schwartz
authors.forename: Jeff D
authors.initials: JD
authors.lastname: Williamson
authors.forename: Tamara B
authors.initials: TB
authors.lastname: Harris
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Kritchevsky
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000097:blood / Q000502:physiology; D015415:Biomarkers / Q000097:blood; D015331:Cohort Studies; D006233:Persons with Disabilities; D005260:Female; D006801:Humans; D008297:Male; D051346:Mobility Limitation; D010281:Parathyroid Hormone / Q000097:blood; D010414:Pennsylvania; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors; D013714:Tennessee; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood
chemical_list: D015415:Biomarkers; D010281:Parathyroid Hormone; D014807:Vitamin D; C104450:25-hydroxyvitamin D