title: An increase in serum 25-hydroxyvitamin D concentrations preceded a plateau in type 1 diabetes incidence in Finnish children.
abstract: BACKGROUND
  In Finland the world-record for the highest incidence of type 1 diabetes has risen steeply over the past decades. However, after 2006 the incidence rate has plateaued. We showed earlier, that despite the strong genetic disease component, environmental factors are driving the increasing disease incidence.
  
  
  OBJECTIVE
  Since vitamin D intake has increased considerably in the country since 2003, we analyzed how serum 25-hydroxyvitamin D (25[OH]D) concentration changed over time in healthy children, and the timely relation of these changes to disease incidence.
  
  
  METHODS
  The birth cohort of the Finnish Type 1 Diabetes Prediction and Prevention project was used to explore longitudinal changes in serum 25-hydroxyvitamin concentrations. The sampling period was limited to children born from 1994 to 2004, with serum samples collected during 1998-2006 in the Turku area, Southwest Finland (60 °N).
  
  
  METHODS
  25(OH)D concentrations were measured every 3-6 months from birth, ages ranging from 0.3 to 12.2 years (387 subjects, 5334 measurements).
  
  
  RESULTS
  Serum 25(OH)D concentrations were markedly lower before 2003 than after (69.3 ± 1.0 nmol/L vs 84.9 ± 1.3 nmol/L, respectively, P < .001) in both genders. The mean difference between the periods was 15.7 ± 1.3 nmol/L (P < .001). Importantly, the frequency of children with low serum 25(OH)D levels (< 50 nmol/L) was reduced to almost half from 2003 (37.3% vs 69.9 %; P < .001). Similarly, severe vitamin D deficiency (<25 nmol/L) also decreased (2.7% vs 7.7%; P = .005). In addition, we detected higher 25(OH)D concentrations in young children (< 2 years) as compared to older children, which is explained by higher vitamin D intake in this group.
  
  
  CONCLUSIONS
  We provide evidence that an increase in circulating concentrations of 25(OH)D shows a delayed temporal association with leveling off of type 1 diabetes incidence in Finland after 2006.
authors: Department of Pediatrics (M.M., V.S., J.M., O.S., J.T., R.H.), University of Turku, 20520 Turku, Finland and Turku University Hospital, 20520 Turku, Finland; Immunogenetics Laboratory (J.I.), University of Turku, 20520 Turku, Finland; Department of Clinical Microbiology (J.I.), University of Eastern Finland, 70211 Kuopio, Finland; Department of Pediatrics (R.V.), University of Oulu, 90014 Oulu, Finland and Oulu University Hospital, 90029 Oulu, Finland; Department of Virology (H.H.), University of Tampere, 33520 Tampere, Finland; Fimlab Laboratories (H.H.), Pirkanmaa Hospital District, 33520 Tampere, Finland; Children's Hospital (M.K.), University of Helsinki and Helsinki University Central Hospital 00029 Helsinki, Finland; Diabetes and Obesity Research Program (M.K.), University of Helsinki, 00014 Helsinki, Finland; Folkhälsan Research Center (M.K.), 00290 Helsinki, Finland; Department of Pediatrics (M.K.), Tampere University Hospital, 33521 Tampere, Finland; and Department of Physiology (J.T.), University of Turku, 20520 Turku, Finland.
authors: Marjaana
authors: M
authors: Mäkinen
authors: Ville
authors: V
authors: Simell
authors: Juha
authors: J
authors: Mykkänen
authors: Jorma
authors: J
authors: Ilonen
authors: Riitta
authors: R
authors: Veijola
authors: Heikki
authors: H
authors: Hyöty
authors: Mikael
authors: M
authors: Knip
authors: Olli
authors: O
authors: Simell
authors: Jorma
authors: J
authors: Toppari
authors: Robert
authors: R
authors: Hermann
mesh_terms: D002648:Child; D002675:Child, Preschool; D003922:Diabetes Mellitus, Type 1 / Q000097:blood / Q000453:epidemiology*; D005260:Female; D005387:Finland / Q000453:epidemiology; D005527:Food, Fortified; D006801:Humans; D015994:Incidence; D007223:Infant; D008297:Male; D014807:Vitamin D / Q000008:administration & dosage* / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood / Q000453:epidemiology*
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D