This article was downloaded by: [University of York] On: 19 August 2014, At: 08:18 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
European Journal of Sport Science Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tejs20
Vitamin D and the athlete: Emerging insights a
b
Daniel J. Owens , William D. Fraser & Graeme L. Close
a
a
Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, UK b
Faculty of Medicine and Health Sciences, Norwich Medical School, University of East Anglia, Norwich, UK Published online: 18 Aug 2014.
To cite this article: Daniel J. Owens, William D. Fraser & Graeme L. Close (2014): Vitamin D and the athlete: Emerging insights, European Journal of Sport Science, DOI: 10.1080/17461391.2014.944223 To link to this article: http://dx.doi.org/10.1080/17461391.2014.944223
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
European Journal of Sport Science, 2014 http://dx.doi.org/10.1080/17461391.2014.944223
REVIEW ARTICLE
Vitamin D and the athlete: Emerging insights
DANIEL J. OWENS1, WILLIAM D. FRASER2, & GRAEME L. CLOSE1 Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, UK; 2Faculty of Medicine and Health Sciences, Norwich Medical School, University of East Anglia, Norwich, UK
Downloaded by [University of York] at 08:18 19 August 2014
1
Abstract Interest in Vitamin D has risen considerably recently with many athletes now advised to take daily vitamin D supplements. The reason for this interest is partly not only attributed to the resurgence of the Vitamin D-deficient disease rickets but also due to the discovery of a Vitamin D receptor in many tissues suggesting a more global role for Vitamin D than previously considered. Unlike the other vitamins that are obtained through the diet, Vitamin D is unique since endogenous synthesis following ultraviolet B (UVB) exposure is the predominant route of entry into systemic circulation. Moreover, Vitamin D could be better classed as a seco-steroid, given that its structure is similar to that of a steroid, and its production is derived from a cholesterol precursor (7-dehydrocholesteol) in the skin. The classification of Vitamin D status is currently subject to considerable debate with many authors opposing governing body recommendations. Regardless of the suggested optimal concentration, there is now growing evidence to suggest that many athletes are in fact Vitamin D deficient, especially in the winter months largely as a consequence of inadequate sun exposure, combined with poor dietary practices, although the consequences of such deficiencies are still unclear in athletic populations. Impaired muscle function and reduced regenerative capacity, impaired immune function, poor bone health and even impaired cardiovascular function have all been associated with low Vitamin D in athletes, however, to date, the majority of studies on Vitamin D have described associations and much more research is now needed examining causation. Keywords: 25-hydroxyvitamin D, 1α,25-dihydroxyvitamin D, muscle, bone, supplementation, ultraviolet B radiation
1. Introduction There are numerous examples that provide evidence that many of the great civilisations heralded the sun for its apparent benefit to human health. In ancient Greece, Herodotus was said to have recommended ‘solaria’ as a cure for weak and flabby muscles, and thus the ancient Greek Olympians were told to train and lie under the sun’s rays (Mercola, 2008). Such observations were made long before the realisation that sunlight was essential for Vitamin D synthesis. In the past decade, we have witnessed a considerable increase in research attention towards the ‘sunlight vitamin’ (Vitamin D), which is in part due to the re-emergence of the preventable bone disorder rickets. In recent years, there have been a number of key findings which have advanced the field considerably, particularly the identification of the Vitamin D receptor (VDR) in many tissues through which Vitamin D exerts many of its effects (reviewed by Demay, 2006). Moreover, the
generation of the VDR knockout mouse (Li et al., 1997) has provided great insight into the multiplicity of roles for Vitamin D. It is now understood that aspects of innate and acquired immunity (Chun, Liu, Modlin, Adams, & Hewison, 2014), bone health (Ebeling, 2014), cardiovascular health (Lavie, Dinicolantonio, Milani, & O’Keefe, 2013) and biological processes within skeletal muscle are just some of the physiological features thought to be regulated by Vitamin D. This review will explore Vitamin D synthesis, considerations when assessing and interpreting measurement of Vitamin D status, the biological actions of Vitamin D relevant to the athlete and protocols for supplementation with Vitamin D.
2. Vitamin D synthesis The human genome has developed the mechanism for Vitamin D synthesis in the skins’ dermis that is
Correspondence: Dr Graeme L. Close, Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Tom Reilly Building, Byrom Street, Liverpool, L3 3AF, UK. E-mail: [email protected] © 2014 European College of Sport Science
Downloaded by [University of York] at 08:18 19 August 2014
2
D. J. Owens et al.
activated by sunlight, or more specifically, ultraviolet B (UVB) radiation (Holick, 1995). During this photosynthetic reaction, the B-ring of 7-dehydrocholesterol (precursor to cholesterol and previtamin D3) is cleaved and resultantly, the thermodynamically unstable previtamin D3 (pre-cholecalciferol) is formed. Thermal isomerisation following this cleavage yields Vitamin D3, a seco-steroid hormone. In human skin, the thermal isomerisation process converts ∼80% of previtamin D3 to Vitamin D3 within 8 hours of exposure to UVB (Tian, Chen, Matsuoka, Wortsman, & Holick, 1993). There are many factors that can affect the dermal synthesis of Vitamin D. For example, the amount of radiation that actually reaches the biosphere (thus available for cutaneous Vitamin D photosynthesis) is a product of wavelength and the amount of ozone that solar radiation must pass, which itself is a function of the solar zenith angle dependent on latitude, season and time of day (Chen, Chimeh et al., 2007). If UVB reaches the skin, another influential factor impacting the subsequent photosynthetic reaction is skin pigmentation as melanin competes with 7-dehydrocholeterol for UVB radiation. Resultantly, those with darker skin require exposure to a stronger source of UVB or more prolonged exposure time to elicit comparable changes in circulating Vitamin D concentration seen in lighter skinned persons (Chen, Chimeh et al., 2007; Clemens, Henderson, Adams, & Holick, 1982). An obvious alternative route for obtaining vital nutrients not naturally synthesised (such as the other vitamins) is through dietary intake. Indeed, there are some, but very few, dietary sources of Vitamin D, although as will become evident, it is unlikely that humans obtain enough Vitamin D from such sources to compensate for a lack of sun exposure. Unlike dermal synthesis that solely produces Vitamin D3, dietary intake provides both Vitamin D2 and D3. Dietary sources of Vitamin D include oily fish, eggs, fortified breakfast cereals, shitake mushrooms and powdered milk. However, intake of these foods appears to be poor in developed countries (Department of Health National Diet and Nutrition Survey, 2011; Hill, O’Brien, Cashman, Flynn, & Kiely, 2004; Moore, Murphy, Keast, & Holick, 2004; Tylavsky, Cheng, Lyytikainen, Viljakainen, & Lamberg-Allardt, 2006). Large-scale investigations have identified that
European Journal of Sport Science Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tejs20
Vitamin D and the athlete: Emerging insights a
b
Daniel J. Owens , William D. Fraser & Graeme L. Close
a
a
Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, UK b
Faculty of Medicine and Health Sciences, Norwich Medical School, University of East Anglia, Norwich, UK Published online: 18 Aug 2014.
To cite this article: Daniel J. Owens, William D. Fraser & Graeme L. Close (2014): Vitamin D and the athlete: Emerging insights, European Journal of Sport Science, DOI: 10.1080/17461391.2014.944223 To link to this article: http://dx.doi.org/10.1080/17461391.2014.944223
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
European Journal of Sport Science, 2014 http://dx.doi.org/10.1080/17461391.2014.944223
REVIEW ARTICLE
Vitamin D and the athlete: Emerging insights
DANIEL J. OWENS1, WILLIAM D. FRASER2, & GRAEME L. CLOSE1 Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, UK; 2Faculty of Medicine and Health Sciences, Norwich Medical School, University of East Anglia, Norwich, UK
Downloaded by [University of York] at 08:18 19 August 2014
1
Abstract Interest in Vitamin D has risen considerably recently with many athletes now advised to take daily vitamin D supplements. The reason for this interest is partly not only attributed to the resurgence of the Vitamin D-deficient disease rickets but also due to the discovery of a Vitamin D receptor in many tissues suggesting a more global role for Vitamin D than previously considered. Unlike the other vitamins that are obtained through the diet, Vitamin D is unique since endogenous synthesis following ultraviolet B (UVB) exposure is the predominant route of entry into systemic circulation. Moreover, Vitamin D could be better classed as a seco-steroid, given that its structure is similar to that of a steroid, and its production is derived from a cholesterol precursor (7-dehydrocholesteol) in the skin. The classification of Vitamin D status is currently subject to considerable debate with many authors opposing governing body recommendations. Regardless of the suggested optimal concentration, there is now growing evidence to suggest that many athletes are in fact Vitamin D deficient, especially in the winter months largely as a consequence of inadequate sun exposure, combined with poor dietary practices, although the consequences of such deficiencies are still unclear in athletic populations. Impaired muscle function and reduced regenerative capacity, impaired immune function, poor bone health and even impaired cardiovascular function have all been associated with low Vitamin D in athletes, however, to date, the majority of studies on Vitamin D have described associations and much more research is now needed examining causation. Keywords: 25-hydroxyvitamin D, 1α,25-dihydroxyvitamin D, muscle, bone, supplementation, ultraviolet B radiation
1. Introduction There are numerous examples that provide evidence that many of the great civilisations heralded the sun for its apparent benefit to human health. In ancient Greece, Herodotus was said to have recommended ‘solaria’ as a cure for weak and flabby muscles, and thus the ancient Greek Olympians were told to train and lie under the sun’s rays (Mercola, 2008). Such observations were made long before the realisation that sunlight was essential for Vitamin D synthesis. In the past decade, we have witnessed a considerable increase in research attention towards the ‘sunlight vitamin’ (Vitamin D), which is in part due to the re-emergence of the preventable bone disorder rickets. In recent years, there have been a number of key findings which have advanced the field considerably, particularly the identification of the Vitamin D receptor (VDR) in many tissues through which Vitamin D exerts many of its effects (reviewed by Demay, 2006). Moreover, the
generation of the VDR knockout mouse (Li et al., 1997) has provided great insight into the multiplicity of roles for Vitamin D. It is now understood that aspects of innate and acquired immunity (Chun, Liu, Modlin, Adams, & Hewison, 2014), bone health (Ebeling, 2014), cardiovascular health (Lavie, Dinicolantonio, Milani, & O’Keefe, 2013) and biological processes within skeletal muscle are just some of the physiological features thought to be regulated by Vitamin D. This review will explore Vitamin D synthesis, considerations when assessing and interpreting measurement of Vitamin D status, the biological actions of Vitamin D relevant to the athlete and protocols for supplementation with Vitamin D.
2. Vitamin D synthesis The human genome has developed the mechanism for Vitamin D synthesis in the skins’ dermis that is
Correspondence: Dr Graeme L. Close, Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Tom Reilly Building, Byrom Street, Liverpool, L3 3AF, UK. E-mail: [email protected] © 2014 European College of Sport Science
Downloaded by [University of York] at 08:18 19 August 2014
2
D. J. Owens et al.
activated by sunlight, or more specifically, ultraviolet B (UVB) radiation (Holick, 1995). During this photosynthetic reaction, the B-ring of 7-dehydrocholesterol (precursor to cholesterol and previtamin D3) is cleaved and resultantly, the thermodynamically unstable previtamin D3 (pre-cholecalciferol) is formed. Thermal isomerisation following this cleavage yields Vitamin D3, a seco-steroid hormone. In human skin, the thermal isomerisation process converts ∼80% of previtamin D3 to Vitamin D3 within 8 hours of exposure to UVB (Tian, Chen, Matsuoka, Wortsman, & Holick, 1993). There are many factors that can affect the dermal synthesis of Vitamin D. For example, the amount of radiation that actually reaches the biosphere (thus available for cutaneous Vitamin D photosynthesis) is a product of wavelength and the amount of ozone that solar radiation must pass, which itself is a function of the solar zenith angle dependent on latitude, season and time of day (Chen, Chimeh et al., 2007). If UVB reaches the skin, another influential factor impacting the subsequent photosynthetic reaction is skin pigmentation as melanin competes with 7-dehydrocholeterol for UVB radiation. Resultantly, those with darker skin require exposure to a stronger source of UVB or more prolonged exposure time to elicit comparable changes in circulating Vitamin D concentration seen in lighter skinned persons (Chen, Chimeh et al., 2007; Clemens, Henderson, Adams, & Holick, 1982). An obvious alternative route for obtaining vital nutrients not naturally synthesised (such as the other vitamins) is through dietary intake. Indeed, there are some, but very few, dietary sources of Vitamin D, although as will become evident, it is unlikely that humans obtain enough Vitamin D from such sources to compensate for a lack of sun exposure. Unlike dermal synthesis that solely produces Vitamin D3, dietary intake provides both Vitamin D2 and D3. Dietary sources of Vitamin D include oily fish, eggs, fortified breakfast cereals, shitake mushrooms and powdered milk. However, intake of these foods appears to be poor in developed countries (Department of Health National Diet and Nutrition Survey, 2011; Hill, O’Brien, Cashman, Flynn, & Kiely, 2004; Moore, Murphy, Keast, & Holick, 2004; Tylavsky, Cheng, Lyytikainen, Viljakainen, & Lamberg-Allardt, 2006). Large-scale investigations have identified that
