Received: 8 August 2018
Accepted: 23 July 2019
First Online: 29 July 2019
Ethics approval and consent to participate
: The study was approved by the ethics committee of the University Hospital Essen (approval number: 15–6607-BO) prior to the start of the survey. All participants gave written informed consent before being included.
: Not applicable.
: Dr. Cramer is a Section Editor with BMC Complementary and Alternative Medicine. Dr. Lauche and Dr. Wardle are Associate Editors with BMC Complementary and Alternative Medicine. The authors declare that they have no further competing interests.