For a decade, with support from the National Geographic Society, I’ve been organizing a study of the places where people live longest. The project grew out of studies by my partners, Dr. Gianni Pes of the University of Sassari in Italy and Dr. Michel Poulain, a Belgian demographer. In 2000, they identified a region of Sardinia’s Nuoro province as the place with the highest concentration of male centenarians in the world. As they zeroed in on a cluster of villages high in Nuoro’s mountains, they drew a boundary in blue ink on a map and began referring to the area inside as the “blue zone.” Starting in 2002, we identified three other populations around the world where people live measurably longer lives than everyone else. The world’s longest-lived women are found on the island of Okinawa. On Costa Rica’s Nicoya Peninsula, we discovered a population of 100,000 mestizos with a lower-than-normal rate of middle-age mortality. And in Loma Linda, Calif., we identified a population of Seventh-day Adventists in which most of the adherents’ life expectancy exceeded the American average by about a decade.