Key Laboratory of Trace Elements and Endemic Diseases of Ministry of Health, School of Public Health, Health Science Center, Xian Jiaotong University, Xian, Peoples Republic of China.|Key Laboratory of Trace Elements and Endemic Diseases of Ministry of Health, School of Public Health, Health Science Center, Xian Jiaotong University, Xian, Peoples Republic of China.|Key Laboratory of Trace Elements and Endemic Diseases of Ministry of Health, School of Public Health, Health Science Center, Xian Jiaotong University, Xian, Peoples Republic of China.|Key Laboratory of Trace Elements and Endemic Diseases of Ministry of Health, School of Public Health, Health Science Center, Xian Jiaotong University, Xian, Peoples Republic of China.