Supplementation with 1000 IU vitamin D/d leads to parathyroid hormone suppression, but not increased fractional calcium absorption, in 4-8-y-old children: a double-blind randomized controlled trial.

Double-blind randomized controlled trial in healthy prepubertal children aged 4.0-8.9 years from the Houston area. For the vitamin D3 group, 32 participants were randomized and 31 were analyzed; the trial enrolled children with usual dietary calcium intake in a moderate range and no medication or multivitamin use.

The active regimen was oral vitamin D3, 1000 IU daily for 8 weeks, formulated in almond oil with orange flavor and matched to placebo in appearance. The comparison group received placebo.

Vitamin D3 increased serum 25(OH)D and suppressed PTH, but it did not improve fractional or total calcium absorption over 8 weeks. In the vitamin D3 group, serum 25(OH)D rose from 27.7 6 7.4 ng/mL at baseline to 36.0 6 10.3 ng/mL, while placebo changed from 27.6 6 7.3 to 29.9 6 12.4 ng/mL; the end-of-study between-group difference was significant (P < 0.001). PTH fell from 21.4 6 10.4 pg/mL to 12.9 6 7.1 pg/mL with vitamin D3 versus 18.4 6 10.5 to 17.6 6 10.9 pg/mL with placebo (P < 0.001). End-of-study 1,25(OH)2D did not differ between groups, and no adverse side effects were noted.

The trial was short and included a relatively small sample of healthy children, which limits power and generalizability. Calcium absorption outcomes were assessed only over 8 weeks, so longer-term skeletal effects were not evaluated. Sex was not reported per arm, and the study tested only one vitamin D dose.