1. Department of Maternal and Child Health, School of Public Health; Sun Yat-Sen University; Guangzhou Guangdong 510080 China
2. Health Promotion Centre for Primary and Secondary Schools of Guangzhou Municipality; Guangzhou Guangdong 510180 China
3. Department of Nutrition and Food Hygiene, Guangdong Provincial Key Laboratory of Tropical Disease Research, School of Public Health; Southern Medical University; Guangzhou Guangdong 510515 China