Nikolaos Koundourakis

By Nikolaos E. Koundourakis and Andrew N. Margioris

Vitamin D is synthesized in the skin following exposure to ultraviolet radiation, producing cholecalciferol, while only a small percentage of the circulating vitamin D is of exogenous origin deriving from food. Following two sequential hydroxylations, in the liver and in the kidneys, vitamin D is fully activated. Although its role in bone physiology and calcium homeostasis is well documented, there is emerging evidence that vitamin D exerts a plethora of additional effects on most tissues regulating the musculoskeletal, cardiovascular, and immune systems as well as energy homeostasis. Its deficiency/insufficiency poses a major public health problem observed in all age groups and regardless of latitude and insolation. In muscles, vitamin D deficiency is associated with a decline in neuromuscular function including muscular strength, walking speed, balance, jumping and sprinting performance, and aerobic capacity, although the evidence is still weak regarding its effects in the young and the athletes. Supplementation counteracts the negative effects of vitamin D deficiency on performance although in individuals with adequate levels of vitamin D, additional supplementation does not appear to enhance further physical capabilities. The aim of this chapter is to review our current understanding of diverse effects of vitamin D in physical performance in athletic and nonathletic populations.

Part of the book: A Critical Evaluation of Vitamin D