Good question. Vit d is under increasing study. I am impressed with how many pts, are deficient. Your doc can do a simple blood test and also monitor if your replacement tx is enough. We know it helps bone regeneration, it is necessary for some meds to work. Eat healthy, and see if you need more supplements if you are losing height or have family hx of osteoporosis.
Probably not. Vitamin d will not likely help with fragile capillaries. I would try vitamins a, c, and e, as they are all necessary for strong collagen and tissue integrity.