Or diet and exercise, which need not be uncorrelated with wealth, but something tells me that places like Sardinia, Okinawa and Nicaragua haven't historically been that wealthy. Especially when you consider that to have the most centenarians now, those centenarians must have been born in the first quarter of the 20th century, 100+ years ago. Whatever effect blue zones have, it's not likely to be an entirely recent one; People don't tend to suddenly gain huge amounts of life expectancy in their middle age.

(Of course, this is all presupposing that the number of centenarians in those areas is not greatly exaggerated, and that there hasn't been a massive migration of centenarians from other areas to the blue zones.)