1. Department of Public Health, Chengdu Medical College, Chengdu City, 610050, China.
2. Department of Nutrition and Food Hygiene, School of Preventive Medicine, The Third Military Medical University, Chongqing City, 400038, China.
3. Department of Epidemiology and Bio-statistics, School of Public Health, Drexel University, Philadelphia, PA 19102, USA.