title: Prospective study of maternal mid-pregnancy 25-hydroxyvitamin D level and early childhood respiratory disorders.
abstract: BACKGROUND
  Studies suggest that prenatal vitamin D status may be inversely associated with lower respiratory tract infections (LRTIs) early in life. Studies of prenatal vitamin D status and development of asthma have inconsistent findings.
  
  
  METHODS
  We examined the associations of maternal mid-pregnancy 25-hydroxyvitamin D [25(OH)D] level with the frequency of LRTIs by 36 months and with current asthma at 36 months using the Norwegian Mother and Child Cohort Study. Maternal plasma 25(OH)D level was measured using liquid chromatography-tandem mass spectrometry. Respiratory disorders were evaluated by maternal report through questionnaires. LRTIs were analysed in a random sample of 1248 children. Asthma was analysed using a case-control design, including 489 cases and 1183 controls. Multivariable generalised linear models calculated adjusted measures of association.
  
  
  RESULTS
  The median gestational week of sample collection was 18 weeks (range 9, 35). The mean 25(OH)D level was 73.7 nmol/L (standard deviation 23.7). Higher maternal mid-pregnancy 25(OH)D level was associated with a reduced risk of three or more LRTIs by 36 months vs. none, adjusted risk ratio 0.74 [95% confidence interval (CI): 0.58, 0.93] per 20 nmol/L increase. Associations were similar when examining the frequency of LRTIs by 18 months, and the frequency of LRTIs between 18 and 36 months. Maternal mid-pregnancy 25(OH)D level was not significantly associated with current asthma at 36 months, adjusted odds ratio 0.91 [95% CI 0.81, 1.02] per 20 nmol/L increase.
  
  
  CONCLUSIONS
  Higher maternal mid-pregnancy 25(OH)D level was associated with a modestly reduced risk of recurrent LRTIs by 36 months, but was not associated with current asthma at 36 months.
authors.affiliation: Department of Chronic Diseases, Division of Epidemiology, Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: Maria C
authors.initials: MC
authors.lastname: Magnus
authors.forename: Lars C
authors.initials: LC
authors.lastname: Stene
authors.forename: Siri E
authors.initials: SE
authors.lastname: Håberg
authors.forename: Per
authors.initials: P
authors.lastname: Nafstad
authors.forename: Hein
authors.initials: H
authors.lastname: Stigum
authors.forename: Stephanie J
authors.initials: SJ
authors.lastname: London
authors.forename: Wenche
authors.initials: W
authors.lastname: Nystad
mesh_terms: D000328:Adult; D001249:Asthma / Q000453:epidemiology* / Q000209:etiology; D016022:Case-Control Studies; D002648:Child; D002853:Chromatography, Liquid; D005260:Female; D006801:Humans; D009664:Norway; D011247:Pregnancy; D011446:Prospective Studies; D012141:Respiratory Tract Infections / Q000453:epidemiology* / Q000209:etiology; D012307:Risk Factors; D011795:Surveys and Questionnaires; D053719:Tandem Mass Spectrometry; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood* / Q000150:complications
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D
keywords: asthma; lower respiratory tract infection; pregnancy; vitamin D