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 cortisone. Vitamin D-3 is produced by the skin, upon exposure to sunlight, and is essential for the development and maintenance of bones 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 sun's harmful radiation now usually make the supplementary administration of vitamin D-3 necessary to ensure the adequate amount in the body.
Vitamin D-3 is important for healthy cellular growth and immune system function. It is essential for the effective absorption and maintenance of calcium levels in the blood, and is vital for the development of strong bones and teeth.
Low levels of vitamin D-3 are associated with serious diseases, such as multiple sclerosis and cancer, while the lack of vitamin D-3 synthesis during winter is considered responsible for high rates of influenza infection.