Funding for this research was provided by:
Medical Research Council (MR/M021513/1)
China Medical Board (No. 09-984 and No. 12-111)
Received: 17 October 2017
Accepted: 19 February 2018
First Online: 27 February 2018
Ethics approval and consent to participate
: The trial was approved by the Institute Review Board of School of Public Health, Sun Yat-sen University (Ref. 44/2015). Written informed consents were obtained from each study participant.
: Not applicable.
: The authors declare that they have no competing interests.
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