Abstract
OBJECTIVE: We investigated the daily dose of vitamin D needed to achieve serum 25-hydroxyvitamin D [25(OH)D] sufficiency among schoolchildren at risk for deficiency. STUDY DESIGN: The Daily D Health Study was a randomized double-blind vitamin D supplementation trial among racially/ethnically diverse schoolchildren (n = 685) in the northeastern United States. Children were supplemented with vitamin D3 at 600, 1000, or 2000 IU/d for 6 months. Measurements included serum 25(OH)D at baseline (October to December), 3 months (January to March), 6 months (April to June), and 12 months (6 months after supplementation). RESULTS: At baseline, mean ± standard deviation serum 25(OH)D level was 22.0 ± 6.8 ng/mL, with 5.5% severely vitamin D deficient (<12 ng/mL), 34.1% deficient (12 to 19 ng/mL), 49.0% insufficient (20 to 29 ng/mL), and 11.4% sufficient (≥30 ng/mL). The lowest levels of serum 25(OH)D were found among black (17.9 ± 6.7 ng/mL) and Asian children (18.9 ± 4.8 ng/mL), with no baseline differences by weight status. Serum 25(OH)D increased over 6 months in all three dose groups. The 2000 IU/d group achieved a higher mean serum 25(OH)D level than the other two dose groups (33.1 vs 26.3 and 27.5 ng/mL; P < 0.001), with 59.9% of this group attaining sufficiency at 3 months and only 5.3% remaining severely deficient/deficient at 6 months. All dose groups demonstrated a fall in 25(OH)D at 12 months. CONCLUSIONS: Children at risk for vitamin D deficiency benefited from daily sustained supplementation of 2000 IU/d compared with lower doses closer to the current recommended daily allowance for vitamin D intake. This benefit occurred over the winter months, when serum 25(OH)D level tend to fall.