title: Vitamin D deficiency in children with a chronic illness-seasonal and age-related variations in serum 25-hydroxy Vitamin D concentrations.
abstract: BACKGROUND
  Children and adolescents with a chronic illness have potential risk factors for vitamin D deficiency. An optimal vitamin D status might have multiple health effects. This study evaluated vitamin D status and its association with age, gender, and season in a large cohort of chronically ill Finnish patients at a tertiary pediatric outpatient clinic. A cross-sectional register-based study was carried out, involving altogether 1351 children (51% boys, age range 0.2-18 years), who visited the outpatient clinic during 2007-2010 and had their vitamin D status (S-25-OHD) determined. A post-doc analysis was conducted to identify predisposing and preventing factors for vitamin D deficiency.
  
  
  RESULTS
  Almost half (47%) of the S-25-OHD values were consistent with subnormal vitamin D status (S-25-OHD <50 nmol/L) while only 12% were >80 nmol/L. Age and season were the most important determinants for S-25-OHD concentration. Mean S-25-OHD concentration differed between age groups (Kruskal-Wallis; p<0.001), adolescents being at highest risk for vitamin D insufficiency. Young age and vitamin D supplementation were preventive factors for deficiency, while non-Finnish ethnic background was a predisposing factor. S-25-OHD showed significant seasonal variation in children older than 6 years. In the whole cohort, S-25-OHD was on average 13 nmol/L higher in summer than in winter, and the prevalence of vitamin D deficiency ( =  S-25-OHD <37.5 nmol/l) varied from 11% in summer to 29% in winter.
  
  
  CONCLUSIONS
  The finding that almost half of the studied Finnish children with a chronic illness had suboptimal vitamin D status is alarming. Inferior vitamin D status was noted in adolescents compared with younger children, suggesting that imbalance between intake and requirement evolves with age. Although less common during summer, subnormal vitamin D status was still observed in 28% of those evaluated in summer. Clinicians should identify individuals at risk and actively recommend vitamin D supplementation.
authors.affiliation: Children's Hospital, Helsinki University Central Hospital and University of Helsinki, Helsinki, Finland.
authors.forename: Elisa
authors.initials: E
authors.lastname: Holmlund-Suila
authors.forename: Panu
authors.initials: P
authors.lastname: Koskivirta
authors.forename: Tuula
authors.initials: T
authors.lastname: Metso
authors.forename: Sture
authors.initials: S
authors.lastname: Andersson
authors.forename: Outi
authors.initials: O
authors.lastname: Mäkitie
authors.forename: Heli T
authors.initials: HT
authors.lastname: Viljakainen
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D002908:Chronic Disease; D003430:Cross-Sectional Studies; D005260:Female; D005387:Finland / Q000453:epidemiology; D005767:Gastrointestinal Diseases / Q000097:blood* / Q000150:complications / Q000453:epidemiology; D006801:Humans; D007154:Immune System Diseases / Q000097:blood* / Q000150:complications / Q000453:epidemiology; D007223:Infant; D008297:Male; D008659:Metabolic Diseases / Q000097:blood* / Q000150:complications / Q000453:epidemiology; D015995:Prevalence; D012621:Seasons; D013472:Sunlight; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood* / Q000150:complications / Q000453:epidemiology
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D