The two most important forms of vitamin D are cholecalciferol (D3) and ergocalciferol (D2). Vitamin D-3 is structurally similar to steroids, such as testosterone, cholesterol, and cortisol. Vitamin D-3 is produced by the skin during sun exposure and is essential for the growth and maintenance of bone and bone density.

Vitamin D-3 is produced only after the skin has been exposed to ultraviolet radiation. More and more people are avoiding sun exposure. Unfortunately, the fast pace of our lifestyle and the justified fear of the harmful rays of the sun, usually make the additional administration of vitamin D-3 necessary to ensure a sufficient amount in the body.

Vitamin D-3 is important for healthy cell growth and immune system function. It is essential for the efficient absorption and maintenance of calcium levels in the blood, and vital for the development of strong bones and teeth.

Low levels of vitamin D-3 are associated with serious illnesses, such as multiple sclerosis and cancer, and a lack of vitamin D-3 synthesis during the winter is thought to be responsible for high rates of influenza infection.