Funding for this research was provided by:
National Research Foundation of Korea (NRF-2018R1A2B6007070)
Received: 18 February 2019
Accepted: 12 June 2019
First Online: 13 July 2019
Ethics approval and consent to participate
: The present study was conducted according to the guidelines laid down in the Declaration of Helsinki. All procedures for the Korea National Health and Nutrition Examination Survey were approved by the Korea Centers for Disease Control and Prevention Institutional Review Board (IRB No: 2007-02CON-04-P, 2008-04EXP-01-C, 2009-01CON-03-2C, 2010-02CON-21-C, 2011-02CON-06-C, and 2012-01EXP-01-2C), and all participants provided written informed consent.
: Not applicable.
: The authors declare that they have no competing interests.