VDR and vitamin D deficiency: In the most recent years, several papers have addressed the importance of Vitamin D and its intracellular receptor VDR in regulation of gut hemostasis and immune response (38–41), here we aim to go further and present a comprehensive review examining the epidemic of Vitamin D deficiency in Gulf Cooperation Council (GCC) which is an alliance of six Middle Eastern countries—Saudi Arabia, Qatar, Kuwait, the United Arab Emirates, Bahrain, and Oman.