[1] Univ Bristol, Sch Social & Community Med, Bristol, Avon, England
[2] Univ Bristol, MRC CAiTE Ctr, Bristol, Avon, England
[3] Henry Wellcome Labs Integrat Neurosci & Endocrino, Bristol, Avon, England
[4] Cardiff Univ, Dept Primary Care & Publ Hlth, Cardiff, S Glam, Wales
[5] UCL, MRC Unit Lifelong Hlth & Ageing, London, England
[6] London Sch Hyg & Trop Med, London WC1, England
[7] Cardiff Univ, Dept Geriatr Med, Cardiff, S Glam, Wales