What is Vitamin D?
Vitamin D is a fat-soluble nutrient, often referred to as the sunshine vitamin as we get approximately 90% of it from the sun in the form of UVB radiation. Although it's labelled a vitamin, it's actually considered a pro-hormone. Receptors in the skin absorb pre-vitamin D3 and convert it into vitamin D3, which the body is then able to make use of. Typically, only 10% of our intake comes from dietary sources in the form of foods such as oily fish and eggs.
How much do you need?
The current recommendation for vitamin D is set at 400 IU/day, but this is a somewhat ambiguous number as research has shown it to be insufficient in achieving optimal serum levels of >75 nmol/L. In fact, studies have shown consuming 4,000 IU a day to be more beneficial - 10x the recommend dose! In the UK, the sunlight does not contain enough UVB radiation between October and April (the winter months), therefore, during this time it is deemed even more important to consider supplementation to avoid deficiency.
How does it affect performance?
In 2015, Graeme Close, one of the worlds leading researchers in vitamin D, looked at Vitamin D concentration levels in numerous UK sports teams. Amongst the different groups, he found that only the rugby league team had adequate levels of over 50 nmol/L, but not a single team was achieving optimal levels of 75>nmol/L. According to Close (2013), athletes who had levels less <15nmol/L and supplemented with 5,000 IU a day saw an improvement in both their 10m sprint time and vertical jump. Which asks the question why all athletes are not ensuring they are reaching optimal levels to improve their performance. In addition to this, it's supplementing with vitamin D also increases phosphocreatine recovery time (the replenishment of creatine phosphate to perform short bursts of exercise) (Sinha, 2013). In relation to performance in the gym, it's clear to see why this may improve your strength and in turn muscle hypertrophy.
How does it affect our health?
Vitamin D is essential for everyone, not just athletes! We not only require vitamin D to regulate the absorption of calcium and phosphorus, but additionally to optimise our immune health. A study by He et al. (2013) found that individuals who had optimal levels of vitamin D had significantly higher saliva IgA, and suffered less upper respiratory illnesses. Not only did it reduce the number of incidences, but the severity of these were also reduced. Martineau (2017) published a strong meta-analysis just last year suggesting that Vitamin D may be just as important as Vitamin C in regards to the common cold.
Ensuring your levels are optimal
As previously highlighted, absorbing enough Vitamin D from the sun or consuming it through the diet can be challenging. Instead, you could consider using Vitamin D3 supplementation to ensure you reach those levels to optimise your health and performance. Most health shops and supermarkets will have stock, or you could purchase some from a trusted brand such as MyProtein, for a cheap price. The ones linked below contain 2,500 iu (enough for 1 a day), so you could get a years worth of supply for under £10.
*MyProtein Vitamin D3 Link*
Close et al. (2013) The effects of vitamin D(3) supplementation on serum total 25[OH]D concentration and physical performance: a randomised dose-response study. The British Journal of Sports Medicine.
He et al. (2013) Influence of Vitamin D status on respiratory infection incidence and immune function during 4 months of winter training in endurance sport athletes. EIR.
Marineau et al. (2017) Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. The British Medical Journal.