Intervention methods and influencing factors of vitamin D deficiency in Northeast China: a self-controlled trial and randomized controlled trial study.

BACKGROUND: Vitamin D deficiency is common among children in high-latitude regions. However, region-specific intervention strategies remain unclear. Few studies have simultaneously examined outdoor activity intervention, vitamin D supplementation, and genetic polymorphisms. Thus, this study aimed to explore feasible intervention strategies for children in Northeast China. METHOD: Sixty-one children were asked to increase outdoor activities for 8 weeks (June-August). Outdoor activity duration and ultraviolet (UV) intensity were recorded. Changes in serum 25(OH)D3 levels and the association with UV exposure were analyzed. Separately, 289 children were randomized to receive 0, 400, or 800 IU/d vitamin D for 8 weeks. The dose-response relationship between vitamin D intake and serum 25(OH)D3 was analyzed. Effects of CYP2R1 single nucleotide polymorphisms (SNPs) (rs1562902, rs10741657) on supplementation response were also evaluated. RESULTS: Outdoor activity duration increased by 11 min/d, and estimated vitamin D production from UV increased by 60.73 IU/d, but serum 25(OH)D3 did not change significantly (18.52 ± 4.07 vs. 18.25 ± 3.11 ng/ml); this change was not associated with outdoor time, UV intensity, or calculated vitamin D production from UV. In the supplementation trial, serum 25(OH)D3 increased by 8.82 ± 7.53 ng/ml in the 400 IU/d group and 15.06 ± 9.40 ng/ml in the 800 IU/d group. Total vitamin D intake (diet + supplement) was estimated to require at least 733.21 IU/d to achieve serum 25(OH)D3 ≥30 ng/ml. Children with CT/TT genotypes (rs1562902) and AG/GG genotypes (rs10741657) showed a trend of lower sensitivity to supplementation. CONCLUSION: Increasing outdoor activity did not improve vitamin D status in children in Northeast China, but daily supplementation was effective. Dietary vitamin D intake and SNPs should be considered when formulating individualized supplementation doses.