After more than 30 years of smoking, Jean Martin of Manalapan, New Jersey, decided to trade her cigarettes for a pair of running shoes. At age 51, she worked up slowly from a brisk walk to jogging and started feeling pretty good. Then one day her calves began to cramp. When the pain became severe, Jean went to a local hospital and was diagnosed with peripheral artery disease (PAD), a condition that had affected her father. PAD is a narrowing of the arteries carrying blood to the limbs. Smokers are up to 25 times more likely to develop it. Jean had the right idea—quitting—she just didn’t do it soon enough.