An increase in serum 25-hydroxyvitamin D concentrations preceded a plateau in type 1 diabetes incidence in Finnish children

Abstract

Context: 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 vitaminDintake has increased considerably in the country since 2003, weanalyzed 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. Design, Setting and Participants: 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). Main Outcome Measure: 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 <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: Weprovide 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.