Department of Epidemiology & Biostatistics, MRC Centre for Environment and Health, School of Public Health, Faculty of Medicine, Imperial College London, St Mary's Campus, Norfolk Place, London, W21PG, UK. Department of Hygiene and Epidemiology, University of Ioannina Medical School, Ioannina, Greece. Department of Nutrition, Bjørknes University College, Oslo, Norway. Department of Endocrinology, Morbid Obesity and Preventive Medicine, Oslo University Hospital, Oslo, Norway. Department of Epidemiology & Biostatistics, MRC Centre for Environment and Health, School of Public Health, Faculty of Medicine, Imperial College London, St Mary's Campus, Norfolk Place, London, W21PG, UK. a.berlanga@imperial.ac.uk.