Rates of vitamin D deficiency in athletes are increasing.  Vitamin D is essential to our health and well-being.

Although labelled a vitamin, calcitriol (bio-active vitamin D) acts more like a hormone within the body. It is involved in many essential functions well beyond bone health.  Vitamin D is critical to hormonal and immune functions as well as cardiovascular, brain and pancreatic function. With far reaching effects, vitamin D receptors can be found in our skin, epithelial cells, neural cells, immune cells, skin, pancreas, breast tissue, and blood.  Recent research has also found that vitamin D functions as a modulator of up to 1000 genes involved in cellular growth and protein synthesis.

Vitamin D deficiency in athletes – what to look out for

Anemia, chronic fatigue, lower back pain, recurrent colds, stress fractures and muscle weakness are common vitamin D deficiency signs found in athletes.


The resulting impaired muscle strength and weakness may occur due to reduced muscle cell growth and atrophy of fast twitch muscle fibers. Sub optimal vitamin D levels may also have flow on effects of reduced calcium uptake and muscle contraction and relaxation.



A large body of evidence now suggests vitamin D deficiency contributes to seasonal sadness, depression and other mental health issues. Boosting your levels may make all the difference to your outlook on life and well-being.


Vitamin D upregulates gene expression of broad-spectrum antimicrobial peptides which are important regulators in the immune system’s first line of defence. Vitamin D also downregulates expression of inflammatory molecules such as tumour neurosis factor-alpha and interleukin-6.

Randomized control trials have found that vitamin D supplementation is associated with dramatically decreased incidence of colds and flu in athletes, while poor vitamin D status was associated with increased frequency of the common cold, influenza, and gastroenteritis.

Further information on nutrient influences of the immune system can be found in my blog here.


Patients with low bone density or recurrent stress fractures may actually find magnesium deficiency is the underlying driver of poor bone health despite vitamin D supplementation.

Magnesium controls calcium levels within the body. Checking blood calcium is not necessarily reflective of dietary or storage sufficiency within the body as described in my bone mineral blog here.  Blood calcium serum levels are less than 1% of total body levels and serum levels are very tightly controlled by parathyroid hormones and calcitonin.

Serum calcium is not a reflection of your calcium levels, but more a reflection of how well your parathyroid hormone can regulate serum calcium (via vitamin D) and your magnesium levels.

Magnesium deficiency blocks calcium absorption from the intestines, reduces tissue sensitivity to parathyroid hormone and levels of parathyroid hormone.

Magnesium is required for key enzymes involved in the activation and deactivation of vitamin D. Magnesium is also required for vitamin D synthesis binding protein which is the key carrier of vitamin D around the body.  Therefore, some athletes may find it is actually low magnesium that is contributing to poor bone health independent of regular sun exposure.

For information on how to check your mineral status including calcium and magnesium read my mineral testing blog here.


Everyone knows how vitamin D can be made by our body when skin is exposed to sunlight through a complex activation process, however what many people fail to realise is that this process doesn’t always occur efficiently or to sufficient levels required for optimal health.

An individuals’ natural vitamin D production may vary depending on the time of day of sun exposure, season, cloud cover, smog, latitude, skin pigmentation, age, and sunscreen use.

So often I see patients with low levels of vitamin D despite being out in the sun daily. There are several reasons why vitamin D levels drop despite sunlight exposure.

1. As vitamin D is fat soluble and stored in fat cells, individuals with low body fat, are also predisposed to vitamin D inadequacy as their storage tank is smaller.

2. Activation and production of vitamin D is inhibited by magnesium deficiency, inflammation, statin or corticosteroid use and excessive use of sunscreen.

3. Individuals with any form of malabsorption issues, liver or kidney issues, coeliac’s disease, Crohn’s, vegans, and thyroid issues can be prone to deficiencies.

4. Anyone with a history of anemia should also be aware of the bidirectional influence between iron and vitamin D. The activation of vitamin D in the kidneys requires iron containing compounds ferredoxin reductase and ferredoxin. Iron deficiency may therefore contribute to the inactivation of vitamin D. Vitamin D deficiency may also be associated with higher hepcidin (a pro-inflammatory mediator) in the liver.  Hepcidin will elevate ferritin stores and down regulate intestinal absorption of iron from food and impair storage iron release.

5. Diets containing limited seafood, eggs or dairy such as vegan diets may also reduce vitamin D intake.


Levels of vitamin D are optimal around 90 mol/L although pathology ranges are often indicating a lower range for disease prevention.  I like to aim for optimal status, although in patients with autoimmune conditions or a history of cancer, levels of 100-120 mol/L may be beneficial.

Preventing and treating vitamin D deficiency in athletes

Daily sunlight exposure on your skin especially on large areas such as the back, chest, legs and arms (25-60 minutes in winter) without suntan cream, is a great way to keep levels topped up.

Lunchtime exercise with as much skin exposure as possible (within decency) is a great way to give yourself a vitamin D fix especially n winter months.

It is a good idea to check your vitamin D levels bi-annually in autumn and spring or when symptoms arise.

Pathology tests can be undertaken by your general practitioner although I am increasingly observing resistance against preventative testing.  If you experience this situation, please contact us to obtain a direct referral to a pathology collection centre.

Vitamin D supplements may be warranted to boost levels. For further information on the suitability of these options for your particular situation, book in for an individual assessment with our Sports Naturopath Kate Smyth here

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