[1] UCL, Div Surg & Intervent Sci, Fac Med Sci, London WC1E 6BT, England
[2] Univ Southampton, Med Res Council Lifecourse Epidemiol Unit, Southampton SO16 6YD, Hants, England
[3] Univ Edinburgh, Lothian Birth Cohorts, Dept Psychol, Edinburgh EH8 9JZ, Midlothian, Scotland
[4] UCL, Dept Epidemiol & Publ Hlth, London WC1E 6BT, England