Vitamin D is best known for its role in aiding with the absorption of calcium from the digestive system and promoting bone formation. Vitamin D is synthesized by the skin following exposure to ultraviolet rays from sunlight, but many people do not spend enough time outdoors and become deficient in this essential vitamin. Vitamin D deficiency has been associated with numerous health conditions including osteoporosis, rickets, autoimmune conditions, diabetes, SAD (seasonal affective disorder), chronic pain and frequent infections.

There is an obvious need to supplement with extra vitamin D especially in the elderly and children, during the winter, and for people with chronic diseases. Vitamin D3 is the most effective form of supplemental vitamin D (compared to D2, a less absorbable form).