Vitamin D is fat soluble and not found naturally in many foods. The best natural source is the flesh of fatty fish like salmon or fish liver oils. There is also some found naturally in select cheeses, beef liver, and egg yolks. This elusive vitamin is mostly synthesized naturally when the UV rays for the sun come in contact with the skin. Vitamin D promotes calcium absorption in the gut and is often added to milk. Insufficient Vitamin D can cause rickets which results in thin, brittle and misshapen bones. Some other roles it has in the body are reduction of inflammation, modulation of cell growth, neuromuscular and immune functions. Besides dietary inadequacy, Vitamin D deficiency can also be the result of impaired absorption and use, increased requirement, or increased excretion. Veganism and diets that lack milk due to allergy or intolerance are more likely to develop a vitamin D deficiency.