1. Division of Intramural Research, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, North Carolina, USA
2. Norwegian Institute of Public Health, Oslo, Norway
3. Haukeland University Hospital, Bergen, Norway
4. University of Bergen, Bergen, Norway
5. Duke University School of Medicine, Durham, North Carolina, USA
6. Bevital A/S, Laboratoriebygget, Bergen, Norway
7. Department of Biostatistics, Gillings School of Global Public Health, University of North Carolina, Chapel Hill, North Carolina, USA