Objective: Basic and epidemiologic studies on inflammatory bowel disease (IBD) have suggested an association between vitamin D and IBD risk. Though, the literature on IBD - especially pediatric-onset IBD - and vitamin D is still in its cradle. We therefore wanted to examine if levels of 25(OH)D at birth were associated with increased risk of developing pediatric-onset IBD.

Material and methods: A case-cohort study composed of cases diagnosed with Crohn's disease, ulcerative colitis or indeterminate/unclassified colitis and healthy controls. Cases and controls were matched on date of birth and were born in the period 1981-2004. Cases were diagnosed before the age of 18 years. The concentration of 25(OH)D was assessed from neonatal dried blood spots using a highly sensitive liquid chromatography tandem mass spectrometry. Odds ratios (OR) were calculated using conditional logistic regression and two-way ANOVA were used to test for season and birth year 25(OH)D variations. A total of 384 matched pairs were included in the statistical analyses.

Results: No significant association were found between levels of 25(OH)D and IBD risk in the adjusted model (OR [95% CI] (per 25 nmol/L increase), 1.12 [0.88; 1.42], p = 0.35). 25(OH)D levels were found to fluctuate significantly with season (p < 0.001) and year (p < 0.001). Median/Q1-Q3 values for 25(OH)D were 27.1/16.5-39.5 nmol/L for cases and 25.7/16.1-39.4 nmol/L for controls.

Conclusion: Our study do not suggest that a window of vulnerability exist around time of birth in regards to 25(OH)D levels and later pediatric-onset IBD risk.