> The nation's centenarian population is quickly
> approaching 70,000, up from some 28,000 in 1990, according
> to a Census Bureau report released yesterday. Four-fifths
> of the members of the venerable 100+ group are female, and
> largely concentrated in the Midwest's "longevity belt" --
> Iowa, South Dakota, Nebraska, Kansas and Minnesota. --
> Milwaukee Journal Sentinel, 6/17
Have there been any studies into the factors contributing to the existence of the Midwest "longevity belt"? A cursory review of the Net didn't produce any results.