Randomization and blinding
FM
Stratified block randomization was performed according to centers and sex, using a randomized block design with the ratio of 1:1:1:1. Participants were allocated to one of four groups as follows: fortified milk (FM), fortified yogurt (FY), plain milk (PM), and plain yogurt (PY). A staff member who was not involved in data collection, analysis, and reporting accomplished the random allocation using sequentially numbered, opaque, sealed envelopes.Blinding was at four levels (total blinding): participants, investigators, outcome assessors, statistician and researcher responsible for randomizing subjects.