Across the arc of medical history, the dream has always been to see illness before it speaks — and now, blood tests can detect Alzheimer's-related changes three to six years before a person notices anything wrong. Yet the deeper story emerging from recent research is not about what science can find, but about what individuals can do once they know: the ancient prescriptions of movement, nourishment, sleep, and human connection turn out to be among the most powerful medicines available. Prevention, it seems, is less a medical event than a sustained way of living — and the challenge now is wheth