Thomas Perls, 49
(VERNON DOUCETTE—BOSTON UNIVERSITY PHOTOGRAPHY)
Director, New England Centenarian Study at Boston University Medical Center
What he does: Tries to donate blood every eight weeks.
Why: He believes that moderate iron deficiency may be good. Iron stimulates cells to churn out free radicals, molecules that may contribute to cancer and other diseases of aging. Women tend to outlive men and are generally better at postponing the onset of age-related diseases, and one theory involves iron loss due to menstruation. "I can't menstruate," says Perls, "but maybe I can donate blood to a blood bank." Besides, it's a good deed. He hopes to live to 95.