Abstract
Previously, known actions of vitamin D were confined to skeletal health, but accumulating evidence has consistently suggested that vitamin D has pleomorphic roles in overall human physiology. Hence, no other micronutrient deficiency in the modern times has gained as much global attention as vitamin D deficiency. In this chapter, the author reinforces what is already known in vitamin D and highlights several important findings in vitamin D research, with a special focus on one of the most vitamin D-deficient regions in the world, the Middle East, and Saudi Arabia, in particular.