Vitamin D and running: levels, foods and supplements

Vitamin D helps the body absorb calcium and maintain normal bone and muscle function, both important considerations for runners. A sustained deficiency can harm bone health and cause muscle weakness, but training outdoors does not necessarily guarantee adequate levels. Nor is there evidence that taking more than needed makes people run faster or prevents every injury.

Vitamin D status depends on sun exposure, diet, age and certain medical circumstances. When risk factors or relevant symptoms are present, a healthcare professional may consider a blood test and prescribe treatment if appropriate. Supplements are not essential for every athlete, and high doses taken without supervision can be harmful.

What vitamin D does when you run

This vitamin helps the intestine absorb calcium and phosphorus, minerals needed to maintain the skeleton. It also plays a role in muscle function and immune processes. The body can make it in the skin when exposed to sunlight and obtain it from some foods, although dietary amounts are often limited.

Each foot strike sends a load through the bones. These tissues renew themselves and adapt to training, but they need enough time and resources. If training load rises too quickly or recovery is inadequate, bone stress injuries can occur. Vitamin D availability is only one part of that balance: calcium, total dietary energy and how exercise progresses matter too.

A severe, prolonged deficiency can contribute to osteomalacia, a condition that weakens bones in adults, and may be associated with bone pain and muscle weakness. That does not mean every ache after a run is caused by this vitamin. Fatigue and pain have many possible causes and need an assessment that considers the whole person.

Injury, recovery and performance: what the evidence shows

Some studies have observed an association between low vitamin D levels and musculoskeletal injuries in athletes. A study published in 2026 involving university athletes found such a relationship, but it is an association, not proof of cause and effect. The participants’ characteristics and the way injuries were measured also limit how far the findings can be applied to all recreational runners.

Correcting a diagnosed deficiency is part of healthcare, especially when bone health is affected. However, the evidence does not establish that supplementation alone prevents stress fractures or consistently improves recovery. Someone with low levels may also have an inadequate diet, less sun exposure or other factors that influence injury risk.

As for performance, raising levels beyond what is needed does not guarantee better speed or endurance. More does not mean greater athletic ability. Rest, adequate food intake and an appropriate training load remain essential whether or not a possible deficiency is investigated or treated.

Why running outdoors may not be enough

The skin makes vitamin D when exposed to ultraviolet B radiation. The amount produced varies with season, time of day, latitude, the area of skin exposed, pigmentation and age. Two people training for the same length of time can therefore have different outcomes. Radiation passing through an ordinary window does not allow effective production in the skin.

Spain’s Valencian Community has many hours of sunshine, but that does not guarantee adequate levels all year round. A person may run before dawn, spend the working day indoors or keep most of their skin covered. Available radiation also changes in winter. Living in a sunny area is no substitute for an individual assessment when there are reasons to suspect a deficiency.

Sun exposure must be balanced against preventing skin cancer and sunburn. There is no universal number of minutes that guarantees enough vitamin D without risk: conditions and individual characteristics matter. Sun protection remains important, particularly during long training sessions and when radiation is strong. Sunburn and ultraviolet tanning beds are not recommended as ways to obtain this vitamin.

Who may be at greater risk of deficiency

Risk can be higher with limited sun exposure, older age or darker skin, because production in the skin depends on several factors and may require more exposure. A diet containing few sources of vitamin D can also play a part. For runners who train mainly indoors or very early, actual time in sunlight may be less than their exercise routine suggests.

Some intestinal conditions that make fat absorption difficult, bariatric surgery and certain liver or kidney diseases can affect the availability or metabolism of this vitamin. Some medicines also have an effect. Medical history and regular medication are therefore more useful for assessing risk than weekly mileage alone.

Highly restrictive diets deserve attention for another reason: they may provide too little energy as well as insufficient nutrients. In athletes, sustained low energy availability can affect bone and hormonal health in both women and men. Absent or irregular periods, repeated injuries and unintentional weight loss are signs that warrant professional advice.

Symptoms and signs worth discussing with a clinician

A low concentration does not always cause symptoms. When deficiency is severe, it may be accompanied by bone pain, muscle weakness or widespread discomfort. None of these signs confirms a diagnosis on its own: they can also arise from overtraining, lack of sleep, anaemia, thyroid problems or other causes. Blood results are interpreted alongside medical history, not as an automatic explanation for every case of fatigue.

In a runner, pain focused on a bone that increases with impact and persists may indicate a bone stress injury. If this occurs, particularly if it changes the way the person runs or also hurts when walking, it is sensible to stop impact activity and seek a medical assessment. Continuing to train through pain cannot rule out a fracture and may make the injury worse.

Repeated stress fractures, persistent weakness or worsening recovery without an obvious explanation also warrant assessment. A clinician may consider training load, energy and calcium intake, menstrual history where relevant and other tests. Not everyone who runs needs a routine vitamin D test simply because they exercise.

What a blood test measures and how results are interpreted

The usual blood test measures 25-hydroxyvitamin D, also known as 25-OH vitamin D or calcidiol. It is the indicator generally used to assess vitamin D stores. Results may be reported in nanograms per millilitre or nanomoles per litre: 1 ng/ml equals 2.5 nmol/l. The active form of the vitamin is not usually the appropriate test for checking stores.

Cut-off points differ between organisations and clinical settings. As a guide used by health bodies, a result below 12 ng/ml may indicate a risk of deficiency; 12 to less than 20 ng/ml may be inadequate for some people; and 20 ng/ml or above is considered adequate for bone health for most people. Not all specialists use exactly the same thresholds.

A result close to a threshold should not be interpreted in isolation. Age, medical conditions, fracture risk and the reason for testing all influence clinical decisions. There is also no general reason for every athlete to aim for levels of 50 to 70 ng/ml. Raising a number is not a sporting goal in itself, and excessive concentrations can be associated with health problems.

Foods that provide vitamin D

The main dietary sources include oily fish such as salmon, sardines and mackerel. Egg yolks provide smaller amounts, and some mushrooms exposed to ultraviolet radiation can also contain vitamin D. Content varies with the food and how it is produced, so a serving does not always provide the same amount.

Some milk, plant drinks, yoghurts and cereals are fortified, but not every product in these categories contains added vitamin D. The label shows whether it has been added and how much is present per 100 grams or per serving. Fortified foods can be particularly useful in vegetarian or vegan diets, although availability and composition depend on the product.

Nuts, pulses and vegetables can be part of a healthy diet, but they should not be considered reliable sources of this vitamin simply because they are nutritious. The same applies to probiotics: they do not replace a source of vitamin D. Dairy products, calcium-fortified plant drinks and other calcium-rich foods can, however, help meet another important need for bone health.

How much is needed and what the units mean

The European Food Safety Authority sets an adequate intake of 15 micrograms a day for adults, equivalent to 600 international units, or IU, assuming minimal production in the skin. This is a population reference value, not a mandatory supplement dose or a figure specific to runners. Needs and recommendations can vary with age and medical circumstances.

Understanding the conversion helps when reading labels: 1 microgram equals 40 IU. That means 10 micrograms is 400 IU and 25 micrograms is 1,000 IU. The amount may be listed per capsule, per drop or per recommended daily serving; confusing these quantities increases the risk of taking more than intended.

The European tolerable upper intake level for adults is 100 micrograms a day, equivalent to 4,000 IU, from diet and supplements combined. This limit is not a recommended amount or a target for improving performance. A doctor may temporarily prescribe a different regimen to treat a deficiency, with follow-up tailored to the patient.

Supplements: when they may help and their risks

A supplement may be appropriate when a deficiency has been confirmed or a healthcare professional identifies a particular risk. The regimen depends on the result, age, medical conditions, medication and other factors. Some people may need treatment and others may not: running alone does not justify taking a supplement.

Vitamin D is mainly sold as D2 and D3. Both can raise blood levels, although D3 usually does so more effectively. Product choice also depends on its source and dietary preferences. Combining it with vitamin K is not necessary for everyone, and people taking anticoagulants should seek advice before using supplements containing vitamin K.

Vitamin D is fat-soluble, and prolonged excess, mainly from supplements, can raise blood calcium. Possible consequences include nausea, vomiting, intense thirst, frequent urination and kidney damage. High doses taken for months are not harmless. Anyone who develops symptoms after taking a supplement should stop it and consult a healthcare professional; severe symptoms require urgent medical attention.

Follow-up tests, when indicated, depend on the treatment and clinical circumstances. Levels do not rise by the same amount in everyone, and no universal dose guarantees a particular result. Taking several products at once can also lead to an unnoticed duplication of intake, especially when a multivitamin already contains this nutrient.

Bone health depends on more than one vitamin

Vitamin D works alongside calcium, but it cannot make up for an inadequate diet on its own. As a general reference, many adults need around 1,000 milligrams of calcium a day, although recommendations vary with age and the organisation issuing them. Dairy products, some fortified plant drinks, calcium-set tofu and sardines with edible bones are options that can help meet this need.

Total energy intake matters too. A runner who increases mileage without eating enough additional food can remain in a state of low energy availability, even while taking a vitamin D supplement. This can affect training adaptation and bone health. A supplement is not a substitute for meals and cannot by itself correct an overly restrictive diet.

Strength training, reasonable progression of training loads and rest are part of the same picture. After a bone stress injury, checking one vitamin is not enough: the reasons for the injury and the conditions that may encourage it to recur need attention. Caring for these factors throughout the season makes more sense than focusing on a capsule or the final week before a race.

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