title: No association between vitamin D levels around time of birth and later risk of developing oligo- and polyarticular juvenile idiopathic arthritis: a Danish case-cohort study.
abstract: OBJECTIVE
  Basic and epidemiological studies on rheumatic autoimmune diseases have suggested an association between vitamin D levels around time of birth and disease risk. The literature on vitamin D and juvenile idiopathic arthritis (JIA) is scarce. We hypothesized that low levels of 25-hydroxyvitamin D [25(OH)D] around time of birth would be associated with increased risk of oligo- or polyarticular JIA.
  
  
  METHODS
  We conducted a case-cohort study of validated cases diagnosed with oligo- and polyarticular JIA (1993-2012) and controls matched on date of birth. Cases and controls were born in the period 1983-2010. Cases were diagnosed using international criteria. The concentration of 25(OH)D was assessed from neonatal dried blood spot (DBS) samples using high-sensitivity liquid chromatography tandem mass spectrometry (LC-MS/MS). Odds ratios (ORs) were calculated using conditional logistic regression and a two-way analysis of variance (ANOVA) was used to test for season and birth year 25(OH)D variations. A total of 300 matched pairs were included in the statistical analyses.
  
  
  RESULTS
  No significant association was found between levels of 25(OH)D and JIA risk in the adjusted model [OR (per 25 nmol/L increase) 1.2, 95% confidence interval (CI) 0.9-1.6, p = 0.2]. 25(OH)D levels were found to fluctuate significantly with season (p < 0.0001) and year (p < 0.0001). The median level of 25(OH)D was 34.4 nmol/L in cases and 31.5 nmol/L in controls.
  
  
  CONCLUSIONS
  Our study does not support the hypothesis that a window of vulnerability exists around time of birth with regard to 25(OH)D levels and later JIA risk. Further studies should explore whether 25(OH)D levels during early pregnancy or infancy may influence JIA risk.
authors.affiliation: a Copenhagen Diabetes Research Centre (CPH-DIRECT), Department of Paediatrics , Herlev University Hospital , Herlev , Denmark.|b Faculty of Health and Medical Sciences , University of Copenhagen , Copenhagen , Denmark.
authors.forename: S U
authors.initials: SU
authors.lastname: Thorsen
authors.affiliation: c Department of Public Health, Section of Biostatistics , University of Copenhagen , Copenhagen , Denmark.
authors.forename: C B
authors.initials: CB
authors.lastname: Pipper
authors.affiliation: d Paediatric Rheumatology Clinic , Rigshospitalet , Copenhagen , Denmark.|e Department of Paediatrics , Næstved Hospital , Næstved , Denmark.
authors.forename: M
authors.initials: M
authors.lastname: Alberdi-Saugstrup
authors.affiliation: d Paediatric Rheumatology Clinic , Rigshospitalet , Copenhagen , Denmark.
authors.forename: S
authors.initials: S
authors.lastname: Nielsen
authors.affiliation: f Department of Congenital Disorders , Statens Serum Institute , Copenhagen , Denmark.
authors.forename: A
authors.initials: A
authors.lastname: Cohen
authors.affiliation: f Department of Congenital Disorders , Statens Serum Institute , Copenhagen , Denmark.
authors.forename: M
authors.initials: M
authors.lastname: Lundqvist
authors.affiliation: g National Institute of Public Health , University of Southern Denmark , Copenhagen , Denmark.
authors.forename: L C
authors.initials: LC
authors.lastname: Thygesen
authors.affiliation: h Department of Nutrition , Harvard TH Chan School of Public Health , Boston , MA , USA.
authors.forename: A
authors.initials: A
authors.lastname: Ascherio
authors.affiliation: a Copenhagen Diabetes Research Centre (CPH-DIRECT), Department of Paediatrics , Herlev University Hospital , Herlev , Denmark.
authors.forename: J
authors.initials: J
authors.lastname: Svensson
mesh_terms: D001171:Arthritis, Juvenile / Q000097:blood / Q000209:etiology*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D016015:Logistic Models; D011247:Pregnancy; D012306:Risk; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D