Excellent suggestion. That might provide a clue as to which mineral-deficient areas might correlate. Unfortunately, nutrition studies are still so very much in their infancy that the researchers don't even think in terms of vitamin/mineral/amino acid/enzyme synergy yet.
According to Ashmead in this book and elsewhere, even rates of vitamin absorption, let alone utilization, are dependent upon MINERAL levels in the body FIRST -- and even with mineral supplements, first mineral absorption and THEN mineral bio-availability are highly variable and dependent upon many factors, some of which are controllable.
Interesting....I was also thinking about where the US would come in this list....and whether eating habits MIGHT have some effect on preclampsia (which my doc worried about when I was pregnant....years ago.)