The main purpose of this study is to investigate whether and in which doses vitamin D intake is needed in order to maintain an adequate vitamin D status in 4-8 year-old Danish children during wintertime.

The main objective of ODIN Junior is to investigate whether and in which doses vitamin D intake is needed in order to maintain serum 25(OH)D concentrations above deficiency and insufficiency cut-offs (30 nmol/L and 50 nmol/L, respectively) in 4-8 year-old Danish children during the winter time. The children will be randomized to receive tablets with either 10 micrograms/day or 20 microgram/day of vitamin D3 (cholecalciferol), corresponding to one and two times the recommended daily intake in children, or placebo for 20 weeks. Measurements and blood sampling will be performed before the beginning and by the end of the intervention.

Inclusion Criteria:

• 4-8 years at the start of the intervention
• healthy
• of white, Danish/European origin
• children must be Danish-speaking
• parents must read and speak Danish
• not planning a winter vacation south of a latitude of 51°North (corresponding to Surrey, England)

Exclusion Criteria:

• diseases that may interfere with vitamin D or calcium metabolism
• intake of medication known to affect vitamin D or calcium metabolism
• use of vitamin D containing supplements ≥ 4 days/week the last 8 weeks before intervention start and use of any vitamin D containing supplements the last 4 weeks before intervention start
• concomitant participation in other studies involving dietary supplements or blood sampling
• serum calcium > 2.7 mmol/L at baseline