[1] Univ Kent, Ctr Res & Dev, Dept Biosci, Canterbury CT2 7PD, Kent, England
[2] Univ Alabama, Dept Med, Div Gerontol Geriatr & Palliat Care, Birmingham, AL 35294 USA
[3] Univ Alabama, Div Prevent Med, Birmingham, AL 35294 USA
[4] Univ Alabama, Sch Publ Hlth, Dept Biostat, Birmingham, AL 35294 USA
[5] Univ Alabama, Sch Publ Hlth, Dept Epidemiol, Birmingham, AL 35294 USA
[6] Vet Affairs Med Ctr, Dept Med, Birmingham, AL USA