Vitamin D is a vitamin. It can be found in small amounts in a few foods, including fatty fish such as herring, mackerel, sardines and tuna. To make vitamin D more available, it is added to dairy products, juices, and cereals that are then said to be "fortified with vitamin D". But most vitamin D - 80% to 90% of what the body gets - is obtained through exposure to sunlight. Vitamin D can also be made in the laboratory as medicine. 

At the same time, vitamin D is a fat-soluble vitamin, also seen as a hormone precursor acting on calcium and phosphorus metabolism.

Vitamin D3 has the following physiological functions:

1. Increase the absorption of calcium and phosphorus by the body, so that the levels of plasma calcium and plasma phosphorus are saturated.

2. Promote growth and bone calcification, promote the integrity of the teeth.

3. Increase the absorption of phosphorus through the intestinal wall, and increase the reabsorption of phosphorus through the renal tubule.

4. Maintain the normal level of citrate in the blood.

5. Prevent amino acids through the kidneys loss.