Scientists on Monday revealed part of the secret to why a small village in southern Italy has an unusual number of centenarians — low levels of a particular hormone that affects circulation. Italian and US experts have spent the last six months investigating the extraordinary longevity of residents of Acciaroli, where more than one in 10 — 81 at the mayor’s last count — of the village’s population of 700 is over 100 years old. Acciaroli is part of the Cilento coast, an area of outstanding natural beauty where the late US nutritionist Ancel Keys first established convincing evidence of the health benefits of a Mediterranean diet based on olive oil and rich in fresh fruit, vegetables and fish.