Copyright ©The Author(s) 2015. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Diabetes. Jul 10, 2015; 6(7): 896-911
Published online Jul 10, 2015. doi: 10.4239/wjd.v6.i7.896
Metabolic syndrome: A review of the role of vitamin D in mediating susceptibility and outcome
Richard C Strange, Kate E Shipman, Sudarshan Ramachandran
Richard C Strange, Institute for Science and Technology in Medicine, Keele University Medical School, England ST4 6QG, United Kingdom
Kate E Shipman, Sudarshan Ramachandran, Department of Clinical Biochemistry, Good Hope Hospital, Heart of England NHS Foundation Trust, Sutton Coldfield B75 7RR, United Kingdom
Sudarshan Ramachandran, Department of Clinical Biochemistry, University Hospital of North Staffordshire, England ST4 6QG, United Kingdom
Author contributions: Strange RC and Ramachandran S contributed equally to the work performing the literature review and writing the initial manuscript; Shipman KE provided support with proofing and editing the paper; all authors reviewed and edited the manuscript.
Conflict-of-interest statement: None.
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See:
Correspondence to: Dr. Sudarshan Ramachandran, Department of Clinical Biochemistry, Good Hope Hospital, Heart of England NHS Foundation Trust, Rectory Road, Sutton Coldfield B75 7RR, United Kingdom.
Telephone: +44-121-4247246 Fax: +44-121-3111800
Received: August 30, 2014
Peer-review started: August 30, 2014
First decision: December 17, 2014
Revised: January 1, 2015
Accepted: March 5, 2015
Article in press: March 9, 2015
Published online: July 10, 2015

Despite the well-recognised role of vitamin D in a wide range of physiological processes, hypovitaminosis is common worldwide (prevalence 30%-50%) presumably arising from inadequate exposure to ultraviolet radiation and insufficient consumption. While generally not at the very low levels associated with rickets, hypovitaminosis D has been implicated in various very different, pathophysiological processes. These include putative effects on the pathogenesis of neoplastic change, inflammatory and demyelinating conditions, cardiovascular disease (CVD) and diabetes. This review focuses on the association between hypovitaminosis D and the metabolic syndrome as well as its component characteristics which are central obesity, glucose homeostasis, insulin resistance, hypertension and atherogenic dyslipidaemia. We also consider the effects of hypovitaminosis D on outcomes associated with the metabolic syndrome such as CVD, diabetes and non-alcoholic fatty liver disease. We structure this review into 3 distinct sections; the metabolic syndrome, vitamin D biochemistry and the putative association between hypovitaminosis D, the metabolic syndrome and cardiovascular risk.

Keywords: Vitamin D, Hypovitaminosis D, Metabolic syndrome, Type 2 diabetes mellitus, Insulin resistance, Cardiovascular disease, Atherogenic dyslipidaemia, Hypertension, Non-alcoholic fatty liver disease

Core tip: The metabolic syndrome is common, affecting about 40% of Americans. It is defined by combinations of risk factors for cardiovascular disease (CVD) including insulin resistance and abdominal obesity. Research implicates hypovitaminosis D in the causation and phenotype of the syndrome and we present relevant data. While hypovitaminosis appears a risk factor for components of the syndrome and its outcome, the mechanism is unclear. The risks associated with varying levels of hypovitaminosis and the benefits of vitamin replacement are unknown. However, unravelling the association between hypovitaminosis and the syndrome is warranted as even a modest decrease in CVD risk would confer substantial benefits.