Vitamin D3 is essential for healthy bones and teeth. Vitamin D3 provide extra calcium and vitamin D3 to your diet. It is therefore used in conditions where your body's calcium and vitamin D levels need to be increased. Vitamin D3 can be prescribed by doctors for certain bone conditions for example osteoporosis. Studies show that taking calcium and vitamin D3 over a long time can prevent hip and other nonvertebral bone fractures in later life. Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks as the minerals calcite and aragonite (most notably as limestone which contains both of those minerals) and is the main component of pearls and the shells of marine organisms snails and eggs. Calcium carbonate is the active ingredient in agricultural lime and is created when calcium ions in hard water react with carbonate ions to create limescale. It is medicinally used as a calcium supplement or as an antacid but excessive consumption can be hazardous.