VITAL SIGNS Women who breast-feed have a lower risk of developing rheumatoid arthritis, even decades later, researchers have found. And the longer they nurse their babies, the smaller the risk becomes. The findings grow out of the long-term Nurses' Health Study, which has followed the health of more than 120,000 women since 1976. The study, led by Dr. Elizabeth W. Karlson of Brigham and Women's Hospital, a Harvard affiliate, appears in the current issue of Arthritis & Rheumatism. Rheumatoid arthritis, an autoimmune disease that can destroy the joints, affects women much more often than it does men. Some scientists have...