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The ‘sunshine vitamin (D)’, is it really worth the hype?

Summer is upon us which means brighter and longer days, which will also mean an increase in vitamin D production. Vitamin D, in the last decade or so has had a drastic increase in the number of researchers conducting studies mainly on the effects of vitamin D on athletic performance and should this be a supplement that requires regular consumption?


The research has shown that there is a large number of individuals that are subject to vitamin D deficiencies due to their shorter days and/or cloudy climate and throughout the winter months (Morton, 2012).


Why does the sun effect whether you are deficient or not in vitamin D?

Vitamin D is known as the 'sunshine vitamin', given that the greatest source comes from the synthesis in the skin via sunlight (UVB). This synthesis from the sun accounts for roughly 80-90% of your total daily required intake, meaning 10-20% must come from dietary sources (infographic at the bottom of the blog!).


How it is synthesised and metabolised?

As briefly as I can, with a bit of science, I am going to explain how vitamin D is metabolised within the body, stored and utilised for these key body functions. On a sunny day, the UVB radiation from the sun converts 7-dehydrocholesterol in the skin to pre-cholecalciferol (pre vit D3) [Any excess is converted to inert photo products to prevent toxicity within the body- hence why you can spend a whole day in the sun yet not go over the recommended intake of vitamin D. However, this prevention of toxicity can only occur when obtaining vitamin D in natural sources i.e. sun or food sources, supplementation of vitamin D cannot do this!]. Pre-cholecalciferol is then converted into cholecalciferol (vitamin D3) which then is bound to vitamin d-binding protein (DBP) in order to enter circulation, where it reaches the liver and gets converted into 25-hydroxyvitamin D (25[OH]D). 25[OH]D is the biomarker measured to obtain vitamin D blood concentrations. 25[OH]D is then hydroxylated in the kidneys, producing active form of vitamin D (1,25 dihydroxyvitamin D) which can then be transported to the target tissues through the blood stream. The target tissue have a vitamin D receptor (VDR) and therefore can uptake it into the cells.


But why is vitamin D necessary for an individual?

Whether you are an athlete or not, having optimal vitamin D levels is necessary for:

- Bone and skeletal health

- Muscle growth

- Immune function

- Inflammatory regulation

- Athletic performance


The latter (athletic performance) is what has received a large amount of attention in the past few years, with the pressure of becoming the best athlete within your sport, athletes and their coaches are now looking at the smallest parts of athletes training programmes and diet to see where the minor changes can be made that give that edge on their peers. However, this does not mean consumed more than required vitamin D levels. The positive effects of vitamin D come from the athletes ability to maintain adequate status (~75-100nmol.1-1)


Having sub-optimal levels has been associated with long-term and inflammatory diseases such as high blood pressure (hypertension), heart disease (cardio-metabolic), arthritis and certain cancers.

Vitamin D, in the last decade or so has had a drastic increase in the number of researchers conducting studies mainly on the effects of vitamin D on athletic performance and should this be a supplement that requires regular consumption?


The research has shown that there is a large number of individuals that are subject to vitamin D deficiencies due to their shorter days and/or cloudy climate and throughout the winter months (Morton, 2012).


Why does the sun effect whether you are deficient or not in vitamin D?

Vitamin D is known as the 'sunshine vitamin', given that the greatest source comes from the synthesis in the skin via sunlight (UVB). This synthesis from the sun accounts for roughly 80-90% of your total daily required intake, meaning 10-20% must come from dietary sources (infographic at the bottom of the blog!).


How it is synthesised and metabolised?

As briefly as I can, with a bit of science, I am going to explain how vitamin D is metabolised within the body, stored and utilised for these key body functions. On a sunny day, the UVB radiation from the sun converts 7-dehydrocholesterol in the skin to pre-cholecalciferol (pre vit D3) [Any excess is converted to inert photo products to prevent toxicity within the body- hence why you can spend a whole day in the sun yet not go over the recommended intake of vitamin D. However, this prevention of toxicity can only occur when obtaining vitamin D in natural sources i.e. sun or food sources, supplementation of vitamin D cannot do this!]. Pre-cholecalciferol is then converted into cholecalciferol (vitamin D3) which then is bound to vitamin d-binding protein (DBP) in order to enter circulation, where it reaches the liver and gets converted into 25-hydroxyvitamin D (25[OH]D). 25[OH]D is the biomarker measured to obtain vitamin D blood concentrations. 25[OH]D is then hydroxylated in the kidneys, producing active form of vitamin D (1,25 dihydroxyvitamin D) which can then be transported to the target tissues through the blood stream. The target tissue have a vitamin D receptor (VDR) and therefore can uptake it into the cells.


But why is vitamin D necessary for an individual?

Whether you are an athlete or not, having optimal vitamin D levels is necessary for:

- Bone and skeletal health

- Muscle growth

- Immune function

- Inflammatory regulation

- Athletic performance


The latter (athletic performance) is what has received a large amount of attention in the past few years, with the pressure of becoming the best athlete within your sport, athletes and their coaches are now looking at the smallest parts of athletes training programmes and diet to see where the minor changes can be made that give that edge on their peers. However, this does not mean consumed more than required vitamin D levels. The positive effects of vitamin D come from the athletes ability to maintain adequate status (~75-100nmol.1-1)


Having sub-optimal levels has been associated with long-term and inflammatory diseases such as high blood pressure (hypertension), heart disease (cardio-metabolic), arthritis and certain cancers.




Infographic highlighting key food sources high in vitamin D to help you achieve the recommended daily intake of 400IU.


Key Points:


  • Vitamin D is an essential nutrients that is involved in bone and teeth health, supports immune system and also has shown to positively affect muscle function and repair.

  • Many individuals (especially in the UK due to the mass number of cloudy winter days and shorter light hours) become deficient. Deficiency then negatively impacts muscle and immune functioning.

  • Adults require 400IU per day, with supplementation between 1000-2000IU having shown to have no side effects and corrects deficiencies.

  • Most multi-vitamins contain vitamin D 40-800IU depending on brand.

  • In summer months 15 minutes of sun exposure per day will be enough to maintain concentrations.

  • Avoid doses high as 10,000IU day as this increases vitamin D breakdown which can have negative side-effects.



References and key papers:

Owens DJ, Allison R, Close GL.(2018).Vitamin D and the Athlete: Current Perspectives and New Challenges. Sports Med. 48(Suppl 1):3-16.


Morton JP, Iqbal Z, Drust B, et al. (2012).Seasonal variation in vitamin D status in professional soccer players of the English Premier League. Appl Physiol Nutr Metab. 37:798–802.


Close, G.L., J. Russell, J.N. Cobley, D.J. Owens, G. Wilson, W. Gregson, W.D. Fraser, and J.P. Morton (2013). Assessment of vitamin D concentration in non-supplemented professional athletes and healthy adults during the winter months in the UK: implications for skeletal muscle function. J. Sports Sci. 31:344-353.

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