1. Northwestern University Feinberg School of Medicine; Departments of Preventive Medicine and Medicine (Cardiology); 680 N. Lake Shore Drive, Suite 1400 Chicago IL USA 60611
2. University of Bristol; School of Social and Community Medicine; Canynge Hall Bristol UK BS8 2PS
3. London School of Hygiene & Tropical Medicine; Department of Non-communicable Disease Epidemiology; Keppel Street London UK WC1E 7HT
4. University of Bristol; Musculoskeletal Research Unit; Avon Orthopaedic Centre Southmead Hospital Bristol UK BS10 5NB