Could vitamin d supplements cause calcification of blood vessels?

Generally no. Make sure your calcium is normal. Replacement with 2000 units vitamin d3/day is usually healthy and without side effects. Make sure that your cholesterol, glucose and BP are normal if you have calcification of blood vessels.
Not as recommended. Adult daily vitamin d recommendations is for 400-1000 iu. We believe that those levels are safe. It is possible that excessive vit d supplements can lead to excess calcium problem.