1 MRC Epidemiology Unit & UKCRC Centre for Diet and Activity Research (CEDAR), University of Cambridge, School of Clinical Medicine, Box 285, Cambridge Biomedical Campus, Cambridge, CB2 0QQ, UK.
2 Department of Public Health and Primary Care, School of Clinical Medicine, Box 285, Cambridge Biomedical Campus, Cambridge, CB2 0SR, UK.
3 MRC Epidemiology Unit & UKCRC Centre for Diet and Activity Research (CEDAR), University of Cambridge, School of Clinical Medicine, Box 285, Cambridge Biomedical Campus, Cambridge, CB2 0QQ, UK. jrp63@medschl.cam.ac.uk.