2.1. Study Participants
milk/dairy allergy
The participants were year two or year three children from two kindergartens in Huining County, Gansu Province, Northwest China, who participated in the trial from September 2021 to September 2022. Eligible participants were healthy children aged 4–6 years old. They were willing to drink milk but consumed less for economic reasons. We excluded those who had the following conditions: milk/dairy allergy or intolerance, requiring hospitalization or long-term medication (>1 month), taking supplements of calcium, vitamin D, or other dietary supplements for more than 3 months, and milk consumption of more than 600 mL per week in the past two years. Of the 351 children initially screened, 267 completed and met the screening questionnaire. Finally, 196 (103 girls and 93 boys) children were enrolled in the current trial (All legal guardians of all participants provided informed consent. The study was performed in accordance with the declaration of Helsinki, and the ethics committee of the School of Public Health of Sun Yat-Sen University approved the study. The clinical trial registration number of this research was ChiCTR2100051044.