1. Department of Medicine and
2. Department of Preventive Medicine, Northwestern University Medical School, Chicago, Illinois;
3. Geriatric Department, “I Fraticini,” National Research Institute (INRCA), Florence, Italy;
4. Department of Family and Preventive Medicine, University of California at San Diego, San Diego, California; and
5. Laboratory of Epidemiology, Demography, and Biometry, National Institute on Aging, Bethesda, Maryland.