[1] Univ Bristol, MRC Integrat Epidemiol Unit, Bristol, Avon, England
[2] Univ Bristol, Sch Social & Community Med, Oakfield House, Bristol BS8 2BN, Avon, England
[3] Univ Birmingham, Inst Appl Hlth Res, Birmingham, W Midlands, England
[4] UCL, MRC Unit Lifelong Hlth & Ageing, London, England