Jarrow Formulas® Vitamin D3 (cholecalciferol) may help improve vitamin D status better than equivalent amounts of ergocalciferol (D2).* D3 is also the form produced by skin with UVB exposure (sunlight). Vitamin D3 is converted to its hormonally-active form, calcitriol, which enhances dietary calcium and phosphorous absorption, supports the production of osteocalcin (a structural protein in bone), and stimulates the vitamin D receptor in innate immune cells to support a healthy immune response.*