Per Bendix Jeppesen

All articles published by MDPI are made immediately available worldwide under an open access license. No special permission is required to reuse all or part of the article published by MDPI, including figures and tables. For articles published under an open access Creative Common CC BY license, any part of the article may be reused without permission provided that the original article is clearly cited. For more information, please refer to https://www.mdpi.com/openaccess.

,* José Lisandro Areta Department of Physical Performance, Norwegian School of Sports Sciences, Oslo, Norway Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom ,* , , , , , , , , , and Jørgen Jensen Department of Physical Performance, Norwegian School of Sports Sciences, Oslo, Norway Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, Faculty of Science, University of Copenhagen, Copenhagen, Denmark

Vitamin D as a vitamin is unique as it can be synthesized in the skin in addition to its dietary sources. Dietary sources contain an insufficient quantity of vitamin D unless fortified with this vitamin. It is necessary, therefore, to have sun exposure to get maximum vitamin D for those who are deficient in vitamin D. This cutaneous synthesis of vitamin D, however, is regulated by the excess sunlight exposure which photo-degrade the extra vitamin D to avoid toxicity [ 8 ].