Vitamin D is produced by the skin when it gets exposed to sunlight. Since this vitamin is synthesized by the body under limited conditions, there are chances of it being deficient in the body. There are several reasons for this: many people stay at places where there is less sunlight, also sometimes the nature of work and lifestyle people have does not give them much scope to be out in the sunlight. Many other times, it is sheer unawareness that leads to vitamin D deficiency in human beings.