Funding for this research was provided by:
Grant-in-Aid for Scientific Research (Grants-in-Aid for Young Scientists [B] 24790611)
Grand-in-Aid for Scientific Research (Grand-in-Aid for Scientific Research [A] 18H0406902)
Received: 26 December 2018
Accepted: 23 August 2019
First Online: 13 September 2019
Ethics approval and consent to participate
: The protocol for Study 1 was reviewed and approved by the Ethics Review Board for epidemiological studies of the Faculty of Medicine, Gunma University. The protocol for Study 2 was reviewed and approved by the institutional review boards of Gunma University and the National Institute of Public Health. Written informed consent was obtained for all participants.
: Not applicable.
: The authors declare that they have no competing interests.