Vitamin D is an oil–soluble vitamin, which is also known as the sunshine vitamin. UV rays activate a certain form of cholesterol in our body and change it to vitamin D. If enough sunshine is available only during summer, which is our case in Finland, it is advised to use vitamin D supplements from September until June.

The most important role of vitamin D is to regulate the absorption of calcium in our bodies. The main factor in calcium absorption is the active form of vitamin D, calcitriol. In addition our bodies need vitamin D for blood clotting and heart rate support, decreasing the risk of infection and diabetes, development of bones and teeth and for better absorption of phosphorus.