Shan-shan Yang1, Yi-yan Wang2, Miao Liu2, Lei Wu2, Jian-hua Wang2, Yao He3. 1. Institute of Geriatrics, Chinese PLA General Hospital, Beijing 100853, China; Department of Disease Control,Jinan Military Area Center for Disease Control and Prevention. 2. Institute of Geriatrics, Chinese PLA General Hospital, Beijing 100853, China. 3. Institute of Geriatrics, Chinese PLA General Hospital, Beijing 100853, China. Email: yhe301@x263.net.