School of Public Health, Beijing Key Laboratory of Environmental Toxicology, Capital Medical University, Beijing, China. Program in Nutrition, Department of Health Studies & Applied Educational Psychology, Teachers College, Columbia University, New York city, New York, USA. Department of Obstetrics and Gynecology, Capital Medical University, Beijing, China. Program in Nutrition, Department of Health Studies & Applied Educational Psychology, Teachers College, Columbia University, New York city, New York, USA pak14@tc.columbia.edu yuhlzjl@ccmu.edu.cn. School of Public Health, Beijing Key Laboratory of Environmental Toxicology, Capital Medical University, Beijing, China pak14@tc.columbia.edu yuhlzjl@ccmu.edu.cn.