1. Medical Research Council (MRC) Unit for Lifelong Health and Ageing (K.K.O., D.B., A.K.W., R.H., D.K.), London WC1B 5JU, United Kingdom
2. MRC Epidemiology Unit (K.K.O.), Institute of Metabolic Science, Addenbrooke's Hospital, Box 285, Cambridge CB2 0QQ, United Kingdom
3. MRC Human Nutrition Research (K.W.), Elsie Widdowson Laboratory, Cambridge CB1 9NL, United Kingdom
4. Imaging Science and Biomedical Engineering (J.E.A.), University of Manchester, Manchester Academic Health Science Centre, Manchester M13 9PT, United Kingdom