1. University of Zurich; Epidemiology, Biostatistics and Prevention Institute; Hirschengraben 84 Zurich Switzerland 8001
2. Center for Research in Environmental Epidemiology-CREAL; Barcelona Spain
3. St George's, University of London; Population Health Research Institute; Cranmer Terrace London UK SW17 0RE
4. Katholieke Universiteit Leuven; Research Centre for Cardiovascular and Respiratory Rehabilitation; Leuven Belgium