Vitamin D may decrease from certain medications such as certain anti-seizure, corticosteroids, heparin, certain antibiotics, mineral oil, and antacids; or certain disease states such as celiac disease, Crohn’s disease and Whipple’s disease. You should not go over in supplementation. 2000 IU is the tolerable upper intake level for adults; supplementation over that may cause a risk for toxicity (weak muscles, weak bones, excessive bleeding, and kidney stones). Vitamin D is available through our foods - Fortified milk, breakfast cereals, egg yolks, fatty fish, and fish oils. Sit at a window with the sun shining in for about 1/2 hour (few times a week) and that will help you get enough Vitamin D. Glad to hear your calcium is within normal limits. Since you have been taking vitamin D supplementation for awhile, suggest getting retested.