Minnesota? Minnesota isn't particularly dark. Minneapolis is apparently on the same latitude as Venice, Italy, and I don't think of Venice as particularly dark or gloomy (to be fair, they probably have better weather).

But yeah. Low vitamin D levels are common even with lily white people in Northern Europe, and at least here in Norway everyone with dark skin knows that they need vitamin D supplements. Traditionally, public health recommendation (for everyone) was to take cod liver oil regularly for every month with an R in it.