1Department of Pediatric Research, Institute of Clinical Medicine Oslo University Hospital, University of Oslo Oslo Norway 
2Hormone Laboratory, Department of Medical Biochemistry, Institute of Clinical Medicine Oslo University Hospital, University of Oslo Oslo Norway 
3Division of Epidemiology Norwegian Institute of Public Health Oslo Norway 
4Division of Diagnostic and Intervention, Institute of Clinical Medicine Oslo University Hospital, University of Oslo Oslo Norway 
5Systems Medicine Department Steno Diabetes Centre Gentofte Denmark 
6 VTT Technical Research Centre of Finland Espoo Finland 
Correspondence to: Benedicte Jørgenrud, Hormone Laboratory, Aker Hospital, Oslo University Hospital, Trondheimsveien 235, 0316 Oslo, Norway. Tel: +47 22 89 47 08; fax: +47 22 15 87 96; e‐mail: [email protected]
Received September 14, 2015
Received in revised form November 26, 2015
Accepted December 17, 2015