25-Hydroxyvitamin D3, also called Calcifediol, is a major metabolite of vitamin D formed by hydroxylation in the liver. Of all the circulating forms of Vitamin D3, 25-Hydroxyvitamin D3 is the principal form. It plays a critical role in calcium metabolism, bone health, and immune function. It has also been found to have anti-inflammatory, anti-cancer, and anti-microbial activities.