Well, considering our ozone and how intense the sun is, I think you might get a sunburn in the winter anyway.
All of the UVs make it through, even at our higher latitude.
If you don't know why the sun is making you feel better, or if it is even making MG better, should you risk more problems by treating it? That's only something you and your doc can answer.
What do your kids say about it? Do they have a vote in Mom risking cancer? I know, that's blunt, but kids are funny when it comes to their parents and wanting them around as long as possible!
Annie