Intake of vitamin D and risk of type 1 diabetes: a birth-cohort study.
BACKGROUND
Dietary vitamin D supplementation is associated with reduced risk of type 1 diabetes in animals. Our aim was to ascertain whether or not vitamin D supplementation or deficiency in infancy could affect development of type 1 diabetes.


METHODS
A birth-cohort study was done, in which all pregnant women (n=12055) in Oulu and Lapland, northern Finland, who were due to give birth in 1966 were enrolled. Data was collected in the first year of life about frequency and dose of vitamin D supplementation and presence of suspected rickets. Our primary outcome measure was diagnosis of type 1 diabetes by end of December, 1997.


RESULTS
12058 of 12231 represented live births, and 10821 (91% of those alive) children were followed-up at age 1 year. Of the 10366 children included in analyses, 81 were diagnosed with diabetes during the study. Vitamin D supplementation was associated with a decreased frequency of type 1 diabetes when adjusted for neonatal, anthropometric, and social characteristics (rate ratio [RR] for regular vs no supplementation 0.12, 95% CI 0.03-0.51, and irregular vs no supplementation 0.16, 0.04-0.74. Children who regularly took the recommended dose of vitamin D (2000 IU daily) had a RR of 0.22 (0.05-0.89) compared with those who regularly received less than the recommended amount. Children suspected of having rickets during the first year of life had a RR of 3.0 (1.0-9.0) compared with those without such a suspicion.


CONCLUSIONS
Dietary vitamin D supplementation is associated with reduced risk of type 1 diabetes. Ensuring adequate vitamin D supplementation for infants could help to reverse the increasing trend in the incidence of type 1 diabetes.
Hyppönen
E
E
Department of Paediatric Epidemiology and Biostatistics, Institute of Child Health, WC1N 1EH, London, UK. e.hypponen@ich.ucl.ac.uk
Läärä
E
E
Reunanen
A
A
Järvelin
M R
MR
Virtanen
S M
SM
D000328:Adult; D015331:Cohort Studies; D003922:Diabetes Mellitus, Type 1 / Q000453:epidemiology / Q000517:prevention & control*; D019587:Dietary Supplements; D004522:Educational Status; D005260:Female; D005387:Finland / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D007231:Infant, Newborn; D008297:Male; D010298:Parity; D011247:Pregnancy; D014807:Vitamin D / Q000008:administration & dosage / Q000627:therapeutic use*
D014807:Vitamin D