Funding for this research was provided by:
Japan Society for the Promotion of Science (JP17H01908)
Industrial Disease Clinical Research (170701-01)
Received: 31 October 2019
Accepted: 25 November 2019
First Online: 10 December 2019
: The study was approved by the Ethics Committee of Medical Research, University of Occupational and Environmental Health, Japan.
: Not applicable.
: The authors declare that they have no competing interests.