Vitamin D For Runners: Benefits, Deficiency And Supplements

Vitamin D might not receive as much attention from runners as carbohydrates, protein or electrolytes, but maintaining adequate levels is important for anyone who runs regularly. It plays an important role in bone and muscle health, helps the body absorb calcium and contributes to normal immune function. For runners, this matters because training repeatedly places stress on muscles and bones, making good nutrition an important part of supporting recovery and long term health.

The challenge is that relatively few foods naturally contain much vitamin D. Our bodies can produce it when our skin is exposed to sunlight, but in the UK the sunlight between October and early March is not strong enough for us to make sufficient vitamin D this way. This makes vitamin D particularly relevant during the darker months of the year, when runners can spend plenty of time outdoors without necessarily producing enough.

Vitamin D for runners is therefore less about searching for another performance supplement and more about making sure the body has what it needs to function normally. Correcting a deficiency can be important, but taking increasingly large amounts in the hope of running faster is unlikely to provide additional benefits if your vitamin D status is already adequate.

What Is Vitamin D?

Vitamin D is a fat soluble vitamin that helps regulate calcium and phosphate in the body. These nutrients are needed to maintain healthy bones, teeth and muscles, making vitamin D particularly relevant to people involved in regular weight bearing exercise such as running.

Unlike most vitamins, vitamin D can be produced by the body when the skin is exposed to suitable ultraviolet B radiation from sunlight. This makes sunlight an important source during spring and summer, although factors including the time of year, skin pigmentation, clothing and the amount of time spent outdoors can all influence how much vitamin D someone produces.

Vitamin D can also be obtained from food and supplements, although relatively few foods naturally provide significant amounts. This combination of limited dietary sources and reduced production from sunlight during the UK winter is why supplementation is recommended at certain times of year.

Why Is Vitamin D Important For Runners?

One of vitamin D's most important functions is helping the body absorb calcium, which is essential for maintaining healthy bones. Running repeatedly loads the skeleton, so maintaining good bone health is an important part of staying healthy and being able to train consistently.

Vitamin D is also involved in normal muscle function, while severe deficiency can contribute to muscle weakness. This does not mean taking additional vitamin D will automatically make a runner stronger, particularly when their existing vitamin D status is already adequate.

There has been considerable interest in whether vitamin D supplementation can directly improve athletic performance. Some studies have reported improvements in certain measures of strength, power or aerobic performance, but the overall evidence remains mixed and does not establish a reliable performance benefit for athletes who already have adequate vitamin D levels. For runners, it is better viewed as a nutrient required for normal health and training rather than as a performance enhancing supplement.

Vitamin D And Bone Health

Bone health is perhaps the most important reason runners should pay attention to vitamin D. Running is a weight bearing activity and, when training progresses appropriately and nutrition is adequate, the repeated loading involved can help stimulate the normal process of bone adaptation.

Problems can occur when the stress placed on the skeleton exceeds its ability to recover and remodel. This can contribute to bone stress injuries, ranging from early bone stress reactions to stress fractures, although vitamin D is only one part of a much bigger picture.

Overall energy availability, calcium intake, training load, recovery, hormonal health and previous injuries can all influence bone health. Research has found associations between lower vitamin D levels and stress fractures in some physically active populations, but this does not mean that low vitamin D is responsible for every bone stress injury.

If you experience persistent localised bone pain, particularly pain that becomes worse during running or continues when you are resting, simply taking vitamin D is not an appropriate solution. Bone stress injuries can become more serious if running continues, so persistent or worsening symptoms should be properly assessed.

Read more about common running injuries here.

Can Vitamin D Improve Running Performance?

Some of the claims surrounding vitamin D and athletic performance can be misleading. Correcting a genuine deficiency may help restore normal physiological function, but taking additional vitamin D when you already have enough is not a proven shortcut to faster running.

Research involving athletes has investigated endurance, muscle strength, power, inflammation and recovery. Some studies have produced promising findings, but the results vary considerably and the evidence does not currently show that vitamin D supplementation consistently improves running performance in people who already have adequate levels.

A useful way to think about vitamin D is that a deficiency may potentially interfere with normal health, training and performance. Correcting that deficiency can therefore be worthwhile, but pushing vitamin D levels increasingly higher does not necessarily produce additional benefits.

Are Runners At Risk Of Vitamin D Deficiency?

Being a runner does not automatically mean you will have low vitamin D levels. Runners who regularly train outside during spring and summer may receive considerable sunlight exposure, although outdoor training alone does not guarantee adequate vitamin D.

Winter running in temperate climates is particularly relevant because the sunlight does not contain enough UVB radiation for the skin to produce sufficient vitamin D. You could therefore run outside several times a week throughout winter and still not obtain enough vitamin D from sunlight.

People who spend little time outside, usually cover most of their skin when outdoors or have darker skin are at increased risk of having insufficient vitamin D. Some medical conditions and medicines can also affect vitamin D status, which means two runners following exactly the same training programme could have very different vitamin D levels.

Signs Of Vitamin D Deficiency

Mild vitamin D deficiency may not produce obvious symptoms, which makes it difficult to identify simply by how you feel. Tiredness, aches and poor running sessions have many possible explanations and should not automatically be blamed on vitamin D.

More significant or prolonged deficiency can affect bone and muscle health and may contribute to muscle weakness or bone pain. These symptoms can also have many other causes, so self diagnosing a vitamin D deficiency based on symptoms alone is unreliable.

For runners, unexplained recurring bone injuries or other concerns about deficiency may provide a reason to discuss vitamin D status with a GP or another appropriate healthcare professional. A blood test measuring 25-hydroxyvitamin D, usually written as 25(OH)D, can be used to assess vitamin D status when testing is considered appropriate.

How Much Vitamin D Do Runners Need?

In the UK, the reference nutrient intake for people aged four and over is 10 micrograms of vitamin D per day, equivalent to 400 International Units or 400 IU. There is no separate official vitamin D requirement specifically for recreational runners, so running more miles does not automatically mean you should take a larger dose.

The NHS recommends that adults consider taking a daily supplement containing 10 micrograms of vitamin D during autumn and winter. This is because it is difficult to obtain enough from food alone and the UK sun is not strong enough during these months for the body to make sufficient vitamin D.

People at greater risk of deficiency, including those who have little or no exposure to sunlight and people with darker skin, should consider taking 10 micrograms throughout the year. Individual medical circumstances can be different, so anyone who has been given specific advice about vitamin D should follow the guidance provided by their healthcare professional.

Should Runners Take Vitamin D Supplements?

For runners living in the UK, the general advice is essentially the same as it is for the wider adult population. A daily supplement containing 10 micrograms of vitamin D should be considered during autumn and winter, with some people advised to consider supplementation throughout the year.

This recommendation is intended to help maintain adequate vitamin D status rather than improve running performance directly. You do not need a specialist sports supplement simply because you run, and a standard vitamin D supplement can provide the recommended amount.

Some runners may be advised to take a different dose if a blood test identifies a deficiency or if there is another medical reason. In that situation, the appropriate amount should be determined by a healthcare professional rather than copied from another runner, an influencer or advice found on social media.

Can You Take Too Much Vitamin D?

Although vitamin D is essential, excessive supplementation over a prolonged period can be harmful. Taking too much can cause calcium to build up in the body, a condition known as hypercalcaemia, which can weaken bones and potentially damage the kidneys and heart.

The NHS advises adults not to take more than 100 micrograms, or 4,000 IU, of vitamin D per day unless advised otherwise by a healthcare professional. This is an upper limit rather than a target intake and is ten times the standard UK recommendation of 10 micrograms.

It is particularly worth checking labels if you use several supplements at the same time. A multivitamin, vitamin D tablet and another nutritional supplement could all contain vitamin D, meaning your total intake may be higher than you realise.

Salmon is a great source of Vitamin D

What Are The Best Food Sources Of Vitamin D?

It is difficult to obtain all the vitamin D you need from food alone, but including vitamin D rich foods can still contribute to your overall intake. Oily fish such as salmon, sardines, trout, herring and mackerel are among the best natural dietary sources.

Egg yolks and red meat contain smaller amounts, while vitamin D is also added to some breakfast cereals, fat spreads and other fortified foods. The amount in fortified products varies, so checking the nutritional information can help you understand how much they provide.

Plant based runners should pay particular attention to fortified products because relatively few unfortified plant foods provide meaningful quantities of vitamin D. Some plant based drinks, cereals and other products are fortified, but this should not be assumed simply because a product is marketed as a dairy alternative.

Food should therefore form part of the picture, but during a UK winter it can be difficult to rely on diet alone to provide enough vitamin D. This is one reason the UK advice recommends considering supplementation during autumn and winter.

Vitamin D And Calcium For Runners

Vitamin D and calcium are closely connected because vitamin D helps the body absorb calcium from the diet. Calcium is required for normal bones as well as muscle and nerve function, so runners concerned about bone health should consider their overall nutrition rather than focusing on one nutrient in isolation.

Most adults should be able to obtain the calcium they need from a balanced diet. Dairy products, calcium fortified plant alternatives, some green vegetables, calcium set tofu and fish where the bones are eaten can all contribute to calcium intake.

Runners should also make sure they consume enough overall energy to support their training. Adequate vitamin D and calcium cannot fully compensate for consistently under-fuelling the body, and low energy availability can have important consequences for bone health and athletic performance.

Read more about calcium for runners here.

When Should A Runner Consider A Vitamin D Test?

Routine vitamin D blood testing is not necessary for every healthy runner. However, there are circumstances where discussing testing with a healthcare professional may be appropriate, including symptoms or medical circumstances suggesting deficiency, very limited sunlight exposure or conditions that interfere with nutrient absorption.

A runner experiencing repeated bone stress injuries should not simply assume vitamin D is responsible. Training load, energy availability, calcium intake, hormonal factors, biomechanics and previous injury history may all need to be considered as part of a wider assessment.

If vitamin D deficiency is confirmed, a healthcare professional can recommend an appropriate treatment dose and determine whether follow-up testing is necessary. Treatment for an established deficiency may be different from the general supplementation advice given to the wider population.

The Bottom Line

Vitamin D plays an important role in bone and muscle health, making it a nutrient runners should not overlook. Maintaining adequate vitamin D status is particularly relevant during the UK winter and for runners who have other risk factors for deficiency, but taking more than you need has not been shown to provide an automatic performance advantage.

For most UK adults, the practical advice is straightforward. Consider taking 10 micrograms of vitamin D each day during autumn and winter, include vitamin D rich or fortified foods as part of a balanced diet and seek professional advice if you have a genuine reason to believe you may be deficient.

Getting the basics right is more useful than chasing high dose supplements. For runners, adequate vitamin D should form part of a broader approach that includes sufficient energy intake, calcium, balanced nutrition, sensible training progression and appropriate recovery.

Read more about supplements for runners here.