Sports and Vitamin D - Injury prevention and performance

Updated: Feb 17, 2023

Vitamin D has been shown to play an active role in bone health, immune function, protein synthesis, muscle function, inflammatory response, cellular growth and regulation of skeletal muscle. It is easy to see why researchers have started investigating its influence on athletic performance and injury prevention.

Vitamin D deficiency can lead to injury and a decrease in your sports performance.

According to Ogan and Pritchett Vitamin D insufficiencies are estimated to affect over one billion people worldwide, with over 77% of Americans considered to be Vitamin D deficient. This figure sounded extraordinarily high to me when I first read their article (does the sun not shine over there?) but it quickly became clear how this is possible when they explained the recommended daily allowances and how important the quality of sunshine is (see below).

Why should athletes worry about Vitamin D?

Bone health

Vitamin D is essential for strong bones. It helps to regulate bone growth, density and remodelling and without adequate amounts bone loss or injury occurs. This is partly due to the fact that calcium cannot be absorbed from the intestines without the presence of Vitamin D. Circulating Vitamin D also affects osteoblast (cells that produce bone) function through several different mechanisms.

A trial using female navy recruits where subjects received 800 IU/day of vitamin D for eight weeks, showed the experimental group to have a 20% lower incidence in stress fractures than the placebo group. Stress fractures are most commonly seen among track and field sports (10%–31%) and can significantly influence performance due to pain and may even prevent an athlete from competing.

Muscle function

It is thought that Vitamin D can improve muscle function via pathways inside the cells as well as increasing the efficiency and number of calcium binding sites involved in muscular contractions.

Close et al (2013) wanted to see if a Vitamin D deficiency negatively impacts on an athlete’s performance. They tested a large cohort of athletes during the winter months. Only 1.6% of the athletes were found to have optimal Vitamin D levels. They then split them into 2 groups and gave one group a placebo and the other a Vitamin D supplement. After 8 weeks they founds significant improvements in the 10m sprint performance as well as vertical jump height for athletes who received the supplement compared to the placebo group.

Muscle repair and remodelling

Owen’s et al (2015) has shown that having high levels of Vitamin D in your blood (>30 ng/mL) can allow you to recover quicker from a bout of exercise. There is also evidence that it can help you build higher quality muscle in response to exercise. A recent prospective study found that athletes who were found to have very low levels of Vitamin D (<23.15 ng/mL) during preseason screening were also more prone to muscle injuries if they had a history of previous injury or had to play a lot of games, compared to athletes with normal levels.

Cardiac function

Vitamin D deficiency was first shown to negatively affect heart function about 30 years ago. Most research in this area has been done on the general population. To my knowledge only one study has so far looked at its effect on the hearts of healthy athletes and what they found is alarming. The researchers found that athletes who were classed as severely Vitamin D deficient had significantly smaller hearts than athletes who were classed as being only slightly deficient or within normal ranges.

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Immune function

Vitamin D is very important for a strong immune system and helps to defend the body against acute illness including influenza and the common cold. Runners and endurance athletes are specifically prone to upper respiratory tract infections (e.g. coughs and head colds) and research has found that athletes with higher Vitamin D levels tend to report fewer infections during the winter months.

Inflammation

Low levels of Vitamin D have been shown to be associated with increased inflammatory markers in endurance athletes. Further research is however needed to determine whether this equates to a higher incidence in inflammatory type injuries/disease. Researchers have also found that a combination of aerobic exercise and Vitamin D supplementation had superior effects on the exercise tolerance of asthmatic patients (compared to just exercise or supplements) which may suggest that this combination has an anti-inflammatory effect in the lungs.

Anaemia or iron deficiency

There appears to be a correlation between low Vitamin D levels in the blood and low iron levels. Researchers are not yet quite sure how these 2 are linked but it may be worth checking your Vitamin D levels if you struggle with low blood iron levels.

Who is at risk of being Vitamin D deficient?

The short answer is most of us! Vitamin D is unique in that, unlike other vitamins, it is not primarily obtained from dietary sources. Certain foods e.g. fatty fish and eggs do contain Vitamin D but the majority is produced when the sun shines on our skin. That’s why it’s also called the sunshine vitamin.

Researchers believe that the main reason for this worldwide phenomenon of Vitamin D deficiency is down to our sun-shy lifestyles. Not only do we spend more time working and playing indoors, but we also tend to avoid direct sunshine or slap strong sunscreen on to avoid skin cancer and ageing.

The distance from the equator, season, time of day, cloud cover, pollution, sunblock, skin pigment and age all dictate whether Vitamin D is available from the sun. Vitamin D can only be synthesised if UVB radiation from the sun is absorbed through the skin in adequate amounts.

This means that if you avoid the sun between 10am and 3pm, wear sunblock or cover most of your skin when outside, you may actually be Vitamin D deficient – even in the summer.

During the winter months the angle of the sun prevents UVB radiation from reaching latitudes greater than 35–37 degrees (that includes us in the UK). Therefore Vitamin D cannot be synthesised from the sun in these areas during the winter months.

The table below shows some of the studies that have found different groups of athletes to be deficient. Of note are the Israeli athletes whom you would have thought would get plenty of sunshine!

Table showing the prevalence of Vitamin D deficiency and insufficiency in various athletic populations.

Recommended levels of Vitamin D

It is important to get your head around the fact that researchers distinguish between three levels of Vitamin D in the blood.

Vitamin D deficiency is defined as <20 ng/mL (50 nmol/L)Vitamin D insufficiency defined as 20–32 ng/mL (50–80 nmol/L)Optimal levels are currently seen as >40 ng/mL (100 nmol/L)

It is generally argued that you require levels higher than 20 ng/mL to prevent certain chronic diseases, but that you require levels of above 40 ng/mL for optimal function. It is also only at these higher levels that vitamin D is stored in muscle and fat for future use. There are big differences in recommendations for daily Vitamin D consumption as is demonstrated in the table below showing the National Institute of Medicine and The Endocrine Society’s recommendations.

Table of recommended levels of Vitamin D intake

The recommended daily Vitamin D intake (according to most experts) to maintain optimal Vitamins D status, is at least 1000 IU per day. However, more is required if you start with suboptimal levels. IU stands for international units and for Vitamin D 1 IU equals 0.025 mg.

With these massive differences in recommendations one wonders if it is possible to overdose on Vitamin D? Apparently the amount of Vitamin D produced from 15 min of unprotected sun exposure is 10,000 to 20,000 IU, in a light-skinned individual, which makes most experts believe toxicity to be a rare and unlikely event. There has, however, been increasing reports of people who has suffered from overdoses and national guidelines currently advise that you should not take more than 4000 IU per day.

The sun is the most plentiful source of Vitamin D but certain foods also contain significant levels (salmon, fatty fish, egg yolks and fortified milk, cereal and orange juice). Unfortunately around 50% of dietary intake of Vitamin D is lost during digestion due to poor absorption.

If, like me, you don’t like taking tablets I would suggest that you see if you can find a mouth spray. The one produced by BetterYou has been shown to be more effective at boosting your Vitamin D levels than tablets. I found it at Holland and Barrett and it tastes quite nice. It comes in 2000 and 3000 IU.

It is also worth noting that Vitamin D3 appears to be the best supplement to take. There is mounting evidence that taking Vitamin D2 can actually decrease the amount of active Vitamin D in your blood.

Summary

Vitamin D deficiency can have an influence on athletic performance and injury. If you work indoors, wear sunscreen, avoid the sun between 10am and 3pm or live above 35 degrees latitude you are very likely to have sub-optimal levels of Vitamin D. Only 50% of ingested Vitamin D makes it into the bloodstream

Need more help with your injury? You’re welcome to consult one of the team at SIP online via video call for an assessment of your injury and a tailored treatment plan.

About the Author

Maryke Louw is a chartered physiotherapist with more than 15 years' experience and a Masters Degree in Sports Injury Management. Follow her on LinkedIn, ResearchGate.

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