4. Discussion
BLIND
This randomized clinical trial shows that VD supplementation in doses of 400 IU (D2), 800 IU (D2), and 1000 IU (D3) five times per week for three months was effective in increasing serum 25(OH)D concentrations and reducing VD deficiency in children 12–30 months of age. The best efficacy was observed by giving 1000 IU D3.There are few studies assessing the efficacy of daily doses of vitamin D2-D3 supplementation in increasing the serum 25(OH)D levels in preschool children compared with a control group [Given that natural dietary sources are scarce in VD and that sun exposure is not as frequent as can be expected, even in sunny places such as Mexico [The effect of VD supplementation observed in our study is in accordance with a double-blind VD supplementation trial carried out in children in the northeastern U.S. The study supplemented with three different dosages of vitamin D3 (600, 1000, and 2000 IU/day) and found that children with the highest dosage of vitamin D3 (2000 IU/day) had the highest mean serum concentration of vitamin D3 after six months of supplementation compared with the other two groups (33.1 vs. 26.3 and 27.5 ng/mL; In another RCT conducted in the U.S., children 7 months to 10 years of age received weekly doses equivalent to 400 IU/day or 1000 IU/day during six months. An average increase of 11.8 nmol/l was observed in the 400 IU group and 19.3 nmol/L in the high dose group (similar to our findings: 8.2 nmol/L and 17.3 nmol/L, respectively) [Consistently, in our study, we observed a higher increase in serum 25(OH)D levels associated with a larger vitamin D dose, which is in agreement with the two aforementioned studies.Among the strengths of our study, we can consider its randomized design, with the inclusion of a comparison group: the MM non-vitamin D-supplemented group. Additionally, our study tested the efficacy of two forms of oral VD supplementation (namely D2 ergocalciferol and D3 cholecalciferol) at different doses ranging from 400 IU/day to 1000 IU/day (10 to 24 µg/d).Finally, there were practical difficulties and reasons for testing two available doses of D2 vs. a higher dose of D3; not available in Mexico at the time. We tried to get the supplements from a private pharmaceutical company in Mexico City. Unfortunately, the fact that no one was manufacturing these supplements at the time, and they were not registered at the Mexican equivalent of the FDA, would involve a very time-consuming, as well as an extremely costly process. Therefore, we gave the children what was commercially available in Mexico, which makes sense, from the point of view of the practical implications of the study, and tried an imported D3 supplement, in the hope that the latter would be more effective, as it turned out to be.In our study, the supplements were registered trademarks, and the field workers knew which supplement each child received. However, the researchers and the data analyst were blind in relation to the treatment.