I really enjoyed Dan Buettner's New York Times Magazine article about the Greek island of Ikaria where people seem freakishly long-lived. But I did have a substantial doubt about it inspired by having recently read and reviewed Nate Silver's book The Signal and the Noise, namely couldn't this just be noise?
An awful lot of the article dwells on healthful aspects of the Ikarian lifestyle, but these mostly seem to be fairly generic aspects of the Mediterranean diet and way of life. And I'm very happy to believe that a diet rich in olive oil and plants and low in satured fat featuring plenty of rest and a strong sense of community is healthy. Certainly there seems to be a good deal of evidence pointing this way, both scientific and social scientific. But the interesting think about Ikaria is precisely that the people there live so much longer than the people on the other Greek Isles or elsewhere in the region. But when you think about it, there are an awful lot of smallish communities on the coastal Mediterranean. On average, those communities have a pretty high life expectancy. But you'd also expect there to be some random variance. And you'd expect one small community or another to simply be a statistical outlier. Only 8,000 people live on Ikaria. They might just happen to have unusually longevity-friendly genetics or have lived longer than your average Greek islander through dumb luck. Trying to delve into the details of exactly how the Ikarian lifestyle differs from the lifestyle in other coastal communities in the region could easily end up being overfitting.
If you have a few hundred islands, then one of them is going to be the island where the people live the longest and there isn't necessarily going to be any particularly deep reason that's the case.