Ultra-D3 contains Cholecalciferol 1000 iu (International units). Cholecalciferol (Vitamin D3) which is a fat soluble vitamin, that helps the body to absorb calcium and phosphorous found in food and supplements. Vitamin D is made by the body when skin is exposed to sunlight. Sunscreen, protective clothing, limited exposure to sunlight, dark skin, and age may prevent getting enough vitamin D from the sun, thus leading to Vitamin D3 Deficiency. Thus, Vitamin D3 in Ultra-D3 tablet is essential for calcium absorption in the body. Other uses of Ultra-D3 tablet are: Building and keeping the bones & teeth strong Reducing Fatigue/stress and muscular pains Boosting immunity and increasing resistance against infection Supplement for patients with diabetic complications and Cardio Vascular Diseases as well. Use under medical supervision.