Vitamin D, known as the "sunshine" vitamin, is a yellow crystalline substance with no taste or odor. Along with vitamins A, E, and K, it belongs to fat-soluble vitamins. The two main forms of vitamin D are cholecalciferol or D3 and ergocalciferol or D2. Its main function is to regulate the absorption of calcium, in other words, vitamin D delivers calcium into the bloodstream and transports it to the bones, where it is then utilized by the bones. Additionally, it maintains a normal heart rhythm, preserves the stability of the nervous system, and plays a minor role in controlling insulin secretion.