Vitamins supplements over the counter are not regulated by any one or any credible labs--so much has been written by the lack of oversight in the last few years! Only prescribed supplements should be used, the over the counter's supplements are too often not what they claim to be.
Save your wallet and your health. Where you live should not make much of a difference since a lot of europeans live well North of the 45th parallel with no ill effects! (Minneapolis is almost at that latitude)
For most of us a good well balanced nutrition is by far healthier!
Certainly I'm extremely skeptical of the inflated claims of the supplement industry, and I am also aware that some doctors tout a specific vitamin or supplement as a miraculous cure-all (e.g. Linus Pauling and his belief in mega-doses of Vitamin C). Of course proper diet and exercise is the way to go.
However, some people can't eat properly or exercise enough, and for other people, even proper diet and exercise isn't enough. When legitimate lab results show a deficiency, which it evidently has in my case, then I won't quibble too much over spending $6 on a bottle of 250 (quantity) OTC Vitamin D tablets. The OTC supplement industry certainly could use more oversight, with that I will agree, but
that discussion ultimately could wind up getting into a political argument since some people vehemently shout that "we-don't-need-no-stinkin'-regulations-on-anything".
I'll take my chances with the OTC supplements rather than prescription since our great health care industry has decided to gouge patients at every possible opportunity, but that discussion again would drift into a political minefield.
Some of the OTC supplement manufacturers do appear to be (just) ethical enough to deliver what's actually listed on the bottle; others of course have been found to be lacking.