Ethics approval and consent to participate
NSD
The study was approved by Regional Committee for Medical and Health Research Ethics (REK, 2.2007.248). All study participants have signed a written informed consent form. The data collection, storage and processing were approved by Norwegian Social Science Data Services (NSD, 2007/17221). The study is registered in ClinicalTrials.gov (16.05.2008, NCT00679237). All methods were carried out in accordance with relevant guidelines and regulations.