維生素D的作用一直都被重視，而其多效的作用也越來越被了解。維生素D及其代謝產物除了有維持鈣磷平衡的功能外，也被發現具有調節腎臟，心臟與免疫系統的作用。維生素D在抗發炎，抗凋亡及抗纖維化上的作用對於細胞內的平衡，包含賀爾蒙的分泌，細胞增生與分化也很重要。因此本文將探討維生素D的製造與代謝，功能方面除了介紹於腎臟、骨骼之關係外，亦介紹與免疫、癌症的關聯及在身體不同系統的功能。

The significant role of vitamin D has always been valued, and its additional pleiotropic effects have been explored in this century. Vitamin D and its metabolites function to maintain calcium balance and regulate the kidneys, heart and immune system. Vitamin D’s anti-inflammatory, anti apoptotic and anti-fibrotic effect is important in intracellular balance, including hormone secretion,cell proliferation and differentiation.Therefore, this paper will elaborate on vitamin D’s synthesis and metabolism, relation to immune system and cancer, as well as effects on different organ systems. (J Intern Med Taiwan 2014; 25: 7-14)