What do the Barbagia region of Sardinia, Italy; Okinawa, Japan; Loma Linda, California; Costa Rica’s Nicoya Peninsula; and Ikaria, Greece have in common? According to author Dan Buettner, they’re all Blue Zones – in his words, “cultures where the proportion of healthy 90- or 100-year-olds to the overall population is unusually high.” Drawing together a team of demographers, scientists, and longevity experts, Buettner, a National Geographic writer and competitive cyclist, led a multiyear study of these cultures, revealing dietary and lifestyle choices that have enabled elders to thrive. His book, “The Blue Zones: Lessons for Living Longer from the People Who’ve Lived the Longest,” was a New York Times bestseller.