Jarrow FORMULAS Vitamin D3 (cholecalciferol) is derived from cod liver oil and sheeps wool and is free of Vitamin A. Fat-soluble Vitamin D3 is converted by the kidneys into the hormone calcitriol the activate form of Vitamin D3 which affects a variety of target tissues including bone intestine muscle brain skin and immune cells. Calcitriol enhances calcium and phosphorous absorption and stimulates the synthesis of osteocalcin an important structural protein in bone. Also calcitriol is involved in proper cell differentiation (changing of cell function) including prostate cells.Other products from HerbsPro