All Puritans Pride Vitamin D formulas are D3, a more potent and active form of Vitamin D. Together with Calcium, Vitamin D helps develop strong bones and teeth, and also assists in immune system health. A review study on the benefits of Vit. D recommends increased use of supplements in the U.S. to help ensure optimal health, and that supplementing with 1000 IU of Vit. D3 can be an effective way to accomplish this. Try our new high-potency 1000 IU, 2000 IU, and 5000 IU.