title: Vitamin D intake is inversely associated with rheumatoid arthritis: results from the Iowa Women's Health Study.
abstract: OBJECTIVE
  Vitamin D is a potent regulator of calcium homeostasis and may have immunomodulatory effects. The influence of vitamin D on human autoimmune disease has not been well defined. The purpose of this study was to evaluate the association of dietary and supplemental vitamin D intake with rheumatoid arthritis (RA) incidence.
  
  
  METHODS
  We analyzed data from a prospective cohort study of 29,368 women of ages 55-69 years without a history of RA at study baseline in 1986. Diet was ascertained using a self-administered, 127-item validated food frequency questionnaire that included supplemental vitamin D use. Risk ratios (RRs) and 95% confidence intervals (95% CIs) were estimated using Cox proportional hazards regression, adjusting for potential confounders.
  
  
  RESULTS
  Through 11 years of followup, 152 cases of RA were validated against medical records. Greater intake (highest versus lowest tertile) of vitamin D was inversely associated with risk of RA (RR 0.67, 95% CI 0.44-1.00, P for trend = 0.05). Inverse associations were apparent for both dietary (RR 0.72, 95% CI 0.46-1.14, P for trend = 0.16) and supplemental (RR 0.66, 95% CI 0.43-1.00, P for trend = 0.03) vitamin D. No individual food item high in vitamin D content and/or calcium was strongly associated with RA risk, but a composite measure of milk products was suggestive of an inverse association with risk of RA (RR 0.66, 95% CI 0.42-1.01, P for trend = 0.06).
  
  
  CONCLUSIONS
  Greater intake of vitamin D may be associated with a lower risk of RA in older women, although this finding is hypothesis generating.
authors.affiliation: College of Public Health, University of Iowa, Iowa City.
authors.forename: Linda A
authors.initials: LA
authors.lastname: Merlino
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Curtis
authors.forename: Ted R
authors.initials: TR
authors.lastname: Mikuls
authors.forename: James R
authors.initials: JR
authors.lastname: Cerhan
authors.forename: Lindsey A
authors.initials: LA
authors.lastname: Criswell
authors.forename: Kenneth G
authors.initials: KG
authors.lastname: Saag
mesh_terms: D000368:Aged; D001172:Arthritis, Rheumatoid / Q000453:epidemiology* / Q000517:prevention & control; D002136:Calcium, Dietary / Q000008:administration & dosage; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D011446:Prospective Studies; D012307:Risk Factors; D011795:Surveys and Questionnaires; D014807:Vitamin D / Q000008:administration & dosage*
chemical_list: D002136:Calcium, Dietary; D014807:Vitamin D