I flipped through the book " Blue Zones " at the bookstore the other day. It shows how people in certain geographical regions live longer. It lists out a bunch of common sense ideas - sunlight, diet, social support, etc., - but nothing earth-shattering.
Instead, I would look at blue zones in terms of the gut bacteria hypothesis. For example, one of the first things that came to mind flipping through the book was breastfeeding. I would bet that it is higher in these regions. Let's take the first Blue Zone: Sardinia, Italy. According to this study , Sardinia has the highest rate of breastfeeding across regions of Italy. So maybe it's not just the sun and the olive oil - maybe it's the breastfeeding that's the key in this region.
You could also look at antibiotic use and see its prevalence in the Blue Zones. You could look at a number of gut-related issues and see if there's a connection. My bet is that these factors are even more powerful than the ones listed in the book.