1. School of Public Health, Health Science Center of Xi’an Jiaotong University, Xi’an, P.R. China;
2. NHC Key Laboratory of Trace Elements and Endemic Diseases, Xi’an Jiaotong University, Xi’an, P.R. China;
3. School of Public Health and Management, Ningxia Medical University, Yinchuan, Ningxia, P.R. China;
4. School of Basic Medicine, Ningxia Medical University, Yinchuan, Ningxia, P.R. China;
5. General Hospital of Ningxia Medical University, Yinchuan, Ningxia, P.R. China