Being cognitively challenged at times, that was quite a bit of information to absorb so bear with me if this was in Jack's post. In order to get an adequate amount of D3 one must get an adequate amount of sunlight with ultraviolet B. This is challenging for some in many parts of the country. Not so for the southwestern states. When the weather is cooler, I sit out in the sun for 15 minutes a day give or take. When it is hot, as in now, I will sit by a window. Would sitting by the window be enough?

BTW - I lived most my life on Long Island and CT. Additionally, I know of 4 people that were born and raised in AZ that have MS. So I am not 100% convinced on the vitamin D theory.