Adequate levels of Vitamin D are essential for immune system health and this has been known for quite some time.
Too much of a good thing can also be dangerous - calcification of the arteries can occur with too much Vitamin D.
This is well-addressed in the article:
Similar to Malone, Dr. Dennis Walker, a radiologist, says that people taking vitamin D supplements should get their vitamin D levels checked six to eight weeks after beginning the supplement, adding that “for every 5,000 IU of D3 consider 100 mcg of K2” as vitamin K2 “helps to ensure calcium transported by the vitamin D is absorbed by bones rather than deposited in arteries.”
Not if taken with magnesium and vitamin K2.