Funding for this research was provided by:
Key research funding of Hainan (14A110069, 16A200143)
Key Research and Development Project of Hainan (ZDYF2017095, ZDYF2016135)
Received: 22 August 2017
Accepted: 25 January 2018
First Online: 2 February 2018
Ethics approval and consent to participate
: Prior to investigation and physical examination, we have got the consent from the participants or from their family members such as sons and daughter-in-laws. If the participants could not sign their names because of illiteracy or being cognitive-impaired, their names were signed by their direct relatives after the consent of the participants. The Ethics Committee of the Hainan branch of the Chinese People’s Liberation Army General Hospital (Sanya, Hainan) approved the study protocol (No. of serial: 301hn11201601).
: Not applicable.
: On behalf of all authors, the corresponding author states that there is no conflict of interest.
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