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

Background 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. Objective We tested the impact of vitamin D-supplementation on serum concentrations of 25-hydroxy-vitamin D [25(OH) D] and short-term growth in Mongol children, with very low serum vitamin D levels in winter. Design 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 D-3 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. Results At winter baseline, children had low vitamin D levels, with a mean (+/- SD) serum 25-hydroxy-vitamin 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. Conclusions 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.