Natural Factors Vegan SunVitamin D3 - 1000 IU - Sourced from wild harvested lichen, this plant-based Vitamin D is the natural form (cholecalciferol). Vitamin D3 is the bioactive form of Vitamin D which is necessary for calcium utilization to aid in maintaining and forming strong bones and a healthy immune system. Developed for vegans and vegetarians who are often lacking in Vitamin D.