1. School of Public Health, Peking University Health Science Center, 38 Xueyuan Road, Haidian District, Beijing 100191, China
2. Department of Pediatrics, Peking University Third Hospital, No.49 North Garden Rd., Haidian District, Beijing 100191, China
3. Vanke School of Public Health, Tsinghua University, Beijing 100084, China
4. National Engineering Research Center of Dairy Health for Maternal and Child, Beijing Sanyuan Foods Co. Ltd., Beijing 100163, China