DANIEL J. OWENS, GRAEME L. CLOSE
Liverpool John Moores University, Research Institute for Sport and Exercise Science, Tom Reilly Building, Byrom Street L3 3AF, Liverpool, United Kingdom

Abstract

Vitamin D deficiency is widespread around the globe due to a lack of sunlight exposure as a result of the modern sun shy lifestyle. It is now understood that vitamin D is implicated in the regulation of a multiplicity of cellular processes, including those mediating human skeletal muscle function. Furthermore, emerging data demonstrate that vitamin D deficiency is common in athletic cohorts and this has stimulated concern over the potential effect that this deficiency may have on athletic performance. Consequently there is a growing trend in elite athletes to supplement with vitamin D, although the appropriate endpoint serum 25[OH]D concentration for ‘optimal’ muscle function and the molecular mechanisms mediating vitamin D’s role in muscle are yet to be established. This short review aims to summarize epidemiological data on vitamin D status in athletic cohorts. Moreover, the review will critically assess the current literature indicating a link between vitamin D and muscle function from a molecular perspective and discuss the limited number of human trials that have aimed to assess the potential link between vitamin D status and athletic performance. Finally, unanswered questions and future directions will be addressed.

INTRODUCTION

The importance of sunlight for physical performance has been known for centuries. Indeed ancient Greek Olympians were directed to train under the sun rays presumably due to the benefits to physical health described by the Greek physician Antyllus (1). However only in recent times and with the development of scientific principles have data pointed our understanding of the beneficial effects of sunlight exposure on muscle health and potentially athletic performance, to vitamin D. It is becoming increasingly more evident that vitamin D status worldwide is remarkably poor and the implications this has for human health are growing exponentially. Our understanding of the importance of vitamin D has progressed from its canonical role in calcium and phosphate homeostasis, to include actions within both the innate and acquired immune system (2), cardiovascular disease (3, 4), cancer prevention (5, 6), control of normal cell cycle (7), reduced blood glucose in diabetes type I and II (8, 9), to name just some major emerging roles. It is now apparent that these roles may be explained by vitamin D’s regulation of genomic and non-genomic cellular pathwa ...