Vitamin D supplementation and growth in urban Mongol school children: Results from two randomized clinical trials

<div><p>Background</p><p>Symptomatic vitamin D deficiency is associated with slowed growth in children. It is unknown whether vitamin D repletion in children with asymptomatic serum vitamin D deficiency can restore normal growth.</p><p>Objective</p><p>We tested the impact of vitamin D-supplementation on serum concentrations of 25-hydroxyvitamin D [25(OH)D] and short-term growth in Mongol children, with very low serum vitamin D levels in winter.</p><p>Design</p><p>We conducted two randomized, double-blind, placebo-controlled trials in urban school age children without clinical signs of rickets. The Supplementation Study was a 6-month intervention with an 800 IU vitamin D₃ supplement daily, compared with placebo, in 113 children aged 12–15 years. A second study, the Fortification Study, was a 7-week intervention with 710 ml of whole milk fortified with 300 IU vitamin D₃ daily, compared with unfortified milk, in 235 children aged 9–11 years.</p><p>Results</p><p>At winter baseline, children had low vitamin D levels, with a mean (±SD) serum 25-hydroxyvitamin D [25(OH)D] concentration of 7.3 (±3.9) ng/ml in the Supplementation Study and 7.5 (±3.8) ng/ml in the Fortification Study. The serum levels increased in both vitamin D groups—by 19.8 (±5.1) ng/ml in the Supplementation Study, and 19.7 (±6.1) ng/ml in the Fortification Study. Multivariable analysis showed a 0.9 (±0.3 SE) cm greater increase in height in the vitamin-D treated children, compared to placebo treated children, in the 6-month Supplementation Study (p = 0.003). Although the children in the 7-week Fortification Study intervention arm grew 0.2 (±0.1) cm more, on average, than placebo children this difference was not statistically significant (p = 0.2). There were no significant effects of vitamin D supplements on differences in changes in weight or body mass index in either trial. For the Fortification Study, girls gained more weight than boys while taking vitamin D 3 (p-value for interaction = 0.03), but sex was not an effect modifier of the relationship between vitamin D3 and change in either height or BMI in either trial.</p><p>Conclusions</p><p>Correcting vitamin D deficiency in children with very low serum vitamin D levels using 800 IU of vitamin D3 daily for six months increased growth, at least in the short-term, whereas, in a shorter trial of 300 IU of D fortified milk daily for 7 weeks did not.</p></div

Participant flow (Supplementation Study).

<p>Participant flow (Supplementation Study).</p

Change in vitamin D and growth characteristics by study and intervention arm.

<p>Change in vitamin D and growth characteristics by study and intervention arm.</p

Mean difference (standard error, SE) in growth parameter change between study arms.

<p>Mean difference (standard error, SE) in growth parameter change between study arms.</p

Change in height by quartile of vitamin D at follow-up by study.

<p>Change in height by quartile of vitamin D at follow-up by study.</p

Baseline characteristics of participants by study and intervention arm.

<p>Baseline characteristics of participants by study and intervention arm.</p