Low vitamin D is common with autoimmune illness, for sure with lupus.
Mine tested below normal a couple of years ago so my specialist put me on 2000 units a day. Mine is now at the low normal range.
I take a couple of other supplements, all approved by my medical team. I take CoQ10 for the heart, Andrew Lessman Essential multi vitamins and his eye health vitamin. I feel better than I have in a long time.
I also eat a very high fiber diet and a lot of fruit and veg. Mostly chicken and fish for protein. We have salmon once a week.
A Thrill Of Hope The Weary World Rejoices