title: Cardiorespiratory fitness is independently associated with 25-hydroxyvitamin D in chronic kidney disease.
abstract: OBJECTIVE
  Vitamin D is an established important contributor to muscle function and aerobic metabolism. Hypovitaminosis D is highly prevalent in CKD patients and is associated with increased cardiovascular (CV) mortality via unknown mechanisms. Because aerobic-exercise capacity strongly predicts future CV events, we hypothesized that vitamin D status could be linked to CV outcomes via an effect on maximum aerobic-exercise capacity in patients with CKD and that this effect may be mediated in part via its actions on muscle strength and functional ability.
  
  
  METHODS
  Baseline demographic, anthropometric, and biochemical data were collected in a cross-sectional study of patients with moderate CKD. Peak aerobic capacity was determined during treadmill stress testing using metabolic equivalence of tasks. Physical activity was assessed using the Active Australia questionnaire, grip strength by dynamometer, and functional capacity by "Up & Go" testing.
  
  
  RESULTS
  The study included 85 participants (age 59.5 ± 9.7 years, 60% male, 44% diabetic, 92% Caucasian; mean serum 25-hydroxyvitamin D [25-OHD] 78.4 ± 29.4 nmol/L). We demonstrated that 25-OHD status was independently associated with aerobic-exercise capacity (β = 0.2; P = 0.008). Aerobic-exercise capacity was also predicted by younger age, white race, smaller waist circumference, absence of a previous angina history, and increasing weekly physical activity. However, neither muscle strength nor functional ability were significantly associated with 25-OHD.
  
  
  CONCLUSIONS
  Vitamin D is independently associated with aerobic capacity in CKD patients, and this finding is not explained by changes in muscle strength or functional ability.
authors.affiliation: Department of Nephrology, Princess Alexandra Hospital, Brisbane, Queensland, Australia. william_petchey@health.qld.gov.au
authors.forename: William G
authors.initials: WG
authors.lastname: Petchey
authors.forename: Erin J
authors.initials: EJ
authors.lastname: Howden
authors.forename: David W
authors.initials: DW
authors.lastname: Johnson
authors.forename: Carmel M
authors.initials: CM
authors.lastname: Hawley
authors.forename: Thomas
authors.initials: T
authors.lastname: Marwick
authors.forename: Nicole M
authors.initials: NM
authors.lastname: Isbel
mesh_terms: D000368:Aged; D000704:Analysis of Variance; D015415:Biomarkers / Q000097:blood; D002318:Cardiovascular Diseases / Q000097:blood / Q000209:etiology* / Q000503:physiopathology; D002908:Chronic Disease; D003430:Cross-Sectional Studies; D005080:Exercise Test; D017079:Exercise Tolerance; D005260:Female; D018737:Hand Strength; D006801:Humans; D007674:Kidney Diseases / Q000097:blood / Q000150:complications* / Q000503:physiopathology; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength; D053581:Muscle Strength Dynamometer; D010809:Physical Fitness; D011793:Queensland; D016032:Randomized Controlled Trials as Topic; D011795:Surveys and Questionnaires; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood / Q000150:complications* / Q000503:physiopathology
chemical_list: D015415:Biomarkers; D014807:Vitamin D; C104450:25-hydroxyvitamin D