[1] Northwestern Univ, Feinberg Sch Med, Dept Med, Chicago, IL 60611 USA
[2] Northwestern Univ, Feinberg Sch Med, Dept Prevent Med, Chicago, IL 60611 USA
[3] Northwestern Univ, Feinberg Sch Med, Dept Surg, Chicago, IL 60611 USA
[4] Univ Maryland, Sch Med, Dept Epidemiol & Publ Hlth, Baltimore, MD 21201 USA
[5] Univ Calif San Diego, Dept Family & Prevent Med, San Diego, CA 92103 USA
[6] NIA, Longitudinal Studies Sect, Baltimore, MD 21224 USA