In 2004, journalist and explorer Dan Buettner teamed up with National Geographic and a team of demographers to find the places on Earth where people live measurably longer, then work out why. They called these regions Blue Zones, after the blue ink early researchers used to circle promising areas on a map. Five were eventually confirmed: Okinawa, Japan; Sardinia, Italy; Nicoya, Costa Rica; Ikaria, Greece; and Loma Linda, California, home to a community of Seventh-day Adventists.

What struck Buettner wasn't a single diet or supplement. It was a set of overlapping habits he later called the "Power 9": moving naturally throughout the day rather than exercising in bursts, having a clear sense of purpose, eating until roughly 80 percent full, favouring beans and vegetables over meat, and maintaining close social ties, often within a few hundred metres of home.

Sardinian shepherds, for instance, walk several miles a day across hilly terrain simply doing their job, not because they've scheduled a workout. In Okinawa, older residents often maintain a "moai," a group of lifelong friends who commit to supporting each other, financially and emotionally, from childhood into old age.

Critics have pointed out that some of the original demographic data, particularly from Sardinia, has since faced scrutiny over inconsistent birth records. Even so, the broader pattern, that environment and habit outperform willpower and genetics, remains one of the most cited findings in longevity research today.