The key to a long lucid life may be as simple as a daily bridge game, The New York Times reports. The world's largest study of health and mental acuity in the elderly, begun in 1982, has finally started to figure out what makes a sharp 90-year-old sharp. A University of Southern California study of nonagenarian retirees at a community south of Los Angeles suggests that people who spend three hours or more each day "engrossed in some mental activities like cards, may be at reduced risk of developing dementia," the Times writes. As of yet, it's hard to discern whether the mentally acute stay sharp because they're active, or whether activity can actually cause mental acuity. There's also evidence that people with regular contact with others do better in and outside the home, both mentally and physically.