Vitamin D3, also known as cholecalciferol, is a fat-soluble vitamin that helps maintain strong bones and teeth by supporting healthy serum calcium concentrations.* It does this by promoting calcium absorption in the gastro-intestinal tract, as well as limiting calcium excretion via urine.* It also supports healthy colon function and may enhance the immune system.* Vitamin D occurs naturally in a limited number of food sources, and although it can be synthesized in the body, achieving adequate skin absorption from sun exposure can be challenging throughout the year. Vital Nutrients provides Vitamin D in its active form, D3.