Health problems associated with single, multiple, and the frequency of months of objectively measured long working hours: a cohort study by the National Institute of Occupational Safety and Health, Japan.

"Declarations Conflict of interestsNone. Ethics approvalThe Ethics Committee of the JNIOSH reviewed and approved of the study protocol (Ethics committee approval No. H2812). Informed consentParticipant employees agreed to give their written informed consent via internet. All data were first collected by our research collaborator, an Employee Assistance Program service provider. The dataset without personally identifiable information was transferred to the JNIOSH through a secure information technology network. Conflict of interests None."

"Funding The present work was supported by Industrial Disease Clinical Research Grants from the Japanese Ministry of Health, Labour and Welfare (150903–01 and 180902–01). Fukazawa K and Araki T are employees of an employee assistance program (EAP) service provider (Advantage Risk Management Co., Ltd), which conducted the Stress Check Program/Industrial physician dispatch services to participants' companies. Other authors have no financial interests to disclose."