High-dose vitamin d intervention in infants--effects on vitamin d status, calcium homeostasis, and bone strength.

Randomized, double-blind trial in healthy full-term newborns at Helsinki Maternity Hospital in Helsinki, Finland. Active intervention arms included 38 infants in the 10 g group, 38 in the 30 g group, and 37 in the 40 g group; infants were term, appropriate for gestational age, and followed from age 2 weeks to 3 months.

Healthy term newborns received daily vitamin D3 drops at 10 g (400 IU), 30 g (1200 IU), or 40 g (1600 IU) from age 2 weeks to 3 months. The supplement was vitamin D3 dissolved in medium-chain triglyceride oil; the regimen was compared across dose levels rather than against placebo.

Daily vitamin D3 increased serum 25-hydroxyvitamin D in a clear dose-response manner and was safe over the 3-month infant period. At age 3 months, median S-25-OHD was 88 nmol/L with 10 g, 124 nmol/L with 30 g, and 153 nmol/L with 40 g; the 40 g dose maintained S-25-OHD above 80 nmol/L in all infants. All infants in the 30 g and 40 g groups achieved the Endocrine Society target of at least 75 nmol/L, and 93% of compliant infants in the 10 g group did so. No hypercalcemia was observed; hypercalciuria occurred in 39% overall but did not differ between groups (P = 0.623). Bone turnover markers were unchanged, while tibial bone measures showed a trend toward larger size with higher doses.

The trial was short and relatively small, and the skeletal findings were only trends at 3 months rather than definitive clinical outcomes. Results are specific to healthy term Finnish newborns, and there was no placebo arm to estimate effects against no supplementation.