Intake of vitamin D and risk of type 1 diabetes: a birth-cohort study

Background Dietary vitamin D supplementation is associated with reduced ris k of type 1 diabetes in animals. Our aim was to ascertain whether or not vi tamin D supplementation or deficiency in infancy could affect development o f 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 frequenc y and dose of vitamin D supplementation and presence of suspected rickets. Our primary outcome measure was diagnosis of type 1 diabetes by end of Dece mber, 1997. Findings 12058 of 12231 represented live births, and 10821 (91% of those al ive) children were followed-up at age 1 year. Of the 10366 children include d in analyses, 81 were diagnosed with diabetes during the study. Vitamin D supplementation was associated with a decreased frequency of type 1 diabete s when adjusted for neonatal, anthropometric, and social characteristics (r ate ratio [RR] for regular vs no supplementation 0.12, 95% CI 0.03-0.51, an d irregular vs no supplementation 0.16, 0.04-0.74. Children who regularly t ook the recommended dose of vitamin D (2000 IU daily) had a RR of 0.22 (0.0 5-0.89) compared with those who regularly received less than the recommende d amount. Children suspected of having rickets during the first year of lif e had a RR of 3.0 (1.0-9.0) compared with those without such a suspicion. Interpretation Dietary vitamin D supplementation is associated with reduced risk of type 1 diabetes. Ensuring adequate vitamin D supplementation for i nfants could help to reverse the increasing trend in the incidence of type 1 diabetes.