Vitamin D is a fat soluble vitamin. It is known as ergocalciferol(D2) and cholecalciferol(D3). It promotes calcium absorption, phosphorus absorption and bone mineralization. At present major population are at a risk of vitamin D deficiency due to their lifestyle and limited exposure to sunlight.
Especially, people who are vegans are at a major risk of vitamin D deficiency because most of the food which contains vitamin D are of animal origin. The sources of vitamin D are fortified milk, fish liver oils, small amount are found in butter, liver, egg yolk, canned salmon and also through skin synthesis with exposure to sunlight.
In summer seasons, countries which are far from the equator, UVB radiations from the sun are sufficient source of vitamin D but for rest of the seasons people should make sure that they get enough vitamin D through food and supplements. It is to be remembered that supplements of Vitamin D should be taken under the guidance of a physician because high amounts of these can be toxic.