Introduction: The aim of the study was to compare the effects of a 30 mu g/day vs 10 mu g/day vitamin D supplementation, given during the two first years of life, on oral health at the age of six to seven years.

Methods: In 2013-2016, we conducted a randomized, double-blinded, clinical trial from age 2 weeks to 2 years of daily vitamin D3 supplementation (10 vs 30 mu g), including 975 healthy infants. For the present follow-up study at age 6-7 years, a sample of 123 children underwent oral examination by investigators blinded to the intervention group. Tooth enamel defect and caries findings, oral rinse active matrix metalloproteinase-8 levels, and tooth eruption were recorded. The intervention groups were compared with chi-square and Mann Whitney U tests. Associations of the oral health outcomes were evaluated with correlation analysis and logistic regression.

Results: Of the children (median age 7.4 years, 51% boys), 56% belonged to the 30 mu g intervention group. Developmental defect of enamel (DDE) was found in 39% of the children in the 10 mu g intervention group and in 53% of the 30 mu g group (p = 0.104). In total, 94% of children were vitamin D sufficient (25(OH)D >= 50 nmol/l) and 88% had caries-free teeth. No associations were found between vitamin D intervention group in infancy and oral health or the presence of DDE.

Conclusion: Daily supplementation with 10 mu g vitamin D3 in the Northern Hemisphere seems adequate in healthy children younger than 2 years in ensuring good oral health at early school age.