Vitamin D, tuberculin skin test conversion, and latent tuberculosis in Mongolian school-age children: a randomized, double-blind, placebo-controlled feasibility trial.

Randomized, double-blind, placebo-controlled feasibility trial in Mongolian public schoolchildren aged 12 to 15 years living in a high-tuberculosis-incidence district of Ulaanbaatar. The vitamin D arm randomized 61 participants and the placebo arm randomized 58; most children were BCG-vaccinated and baseline vitamin D deficiency was common.

The active intervention was oral vitamin D3 (cholecalciferol) 800 IU daily by capsule for 6 months, compared with matched placebo. Dosing was taken during the school week and recorded in diaries.

Vitamin D supplementation clearly improved vitamin D status and was associated with modestly greater linear growth, but the reduction in tuberculin skin test conversion did not reach statistical significance in this small trial. Serum 25(OH)D rose from 7.0 ng/mL at baseline to 18.2 ng/mL at 3 months and 19.8 ng/mL at 6 months in the vitamin D group, versus 4.1 and 9.6 ng/mL in placebo. Height gain over 6 months was 2.9 cm with vitamin D versus 2.0 cm with placebo (95% CI for difference 2.16, 2.81; P = 0.0025). TST conversion occurred in 5 of 45 children (11%) with vitamin D versus 11 of 41 (27%) with placebo (RR 0.41, 95% CI 0.16, 1.09; P = 0.06), and no significant adverse events were observed.

This was a small feasibility trial with limited power for tuberculosis outcomes, so the TST conversion analysis was underpowered and imprecise. Follow-up was only 6 months, and the study was conducted in one high-risk Mongolian school population, which limits generalizability. The primary clinical infection endpoint did not reach statistical significance despite favorable directionality.