D3 Must contains Cholecalciferol 2000 iu (International units). Cholecalciferol (Vitamin D3) 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 D3 Must tablet is essential for calcium absorption in the body. Other uses of D3 Must 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.