Nutrients 2013, 5, 3605-3616; doi:10.3390/nu5093605 OPEN ACCESS nutrients ISSN 2072-6643 www.mdpi.com/journal/nutrients Review Vitamin D: Deficiency, Sufficiency and Toxicity Fahad Alshahrani 1 and Naji Aljohani 2,3,4,* 1 Department of Medicine, King Abdulaziz Medical City, Riyadh 14611, Saudi Arabia; E-Mail:
[email protected] 2 Specialized Diabetes and Endocrine Center, King Fahad Medical City, Riyadh 59046, Saudi Arabia; E-Mail:
[email protected] 3 Faculty of Medicine, King Saud bin Abdulaziz University for Health Sciences, Riyadh 22490, Saudi Arabia 4 Prince Mutaib Chair for Biomarkers of Osteoporosis, College of Science, King Saud University, Riyadh 11451, Saudi Arabia * Author to whom correspondence should be addressed; E-Mail:
[email protected]; Tel.: +966-1-467-5939; Fax: +966-1-467-5931. Received: 6 May 2013; in revised form: 21 August 2013 / Accepted: 27 August 2013 / Published: 13 September 2013 Abstract: The plethora of vitamin D studies over the recent years highlight the pleomorphic effects of vitamin D outside its conventional role in calcium and bone homeostasis. Vitamin D deficiency, though common and known, still faces several challenges among the medical community in terms of proper diagnosis and correction. In this review, the different levels of vitamin D and its clinical implications are highlighted. Recommendations and consensuses for the appropriate dose and duration for each vitamin D status are also emphasized. Keywords: vitamin D; vitamin D deficiency; vitamin D toxicity 1. Introduction Vitamin D plays an essential role in the regulation of metabolism, calcium and phosphorus absorption of bone health. However, the effects of vitamin D are not limited to mineral homeostasis and skeletal health maintenance.