Vitamin D deficiency in athletes: recovery, performance and testosterone

A vitamin D deficiency is more common in athletes than you might think, especially in the Dutch winter. A low status is linked to muscle weakness, slower recovery and a tendency to catch colds. The only way to know for sure is to measure your 25-OH vitamin D.

I see the pattern return every year: around February athletes feel flat and blame their training, while their vitamin D sits at rock bottom.

Why do athletes often have a vitamin D deficiency?

Your skin makes vitamin D under sunlight, and in the Netherlands the sun sits too low from October to March for enough production. Athletes who train indoors or are outside only early and late miss that exposure entirely. As a result the status drops in exactly the season you want to keep training hard.

A darker skin and the use of sunscreen lower production further. So it is not a matter of poor eating, but of too little sun.

Which symptoms come with a deficiency?

The complaints are vague and resemble ordinary fatigue, which makes a deficiency easy to mask. Commonly mentioned signs of a low vitamin D status are muscle weakness, muscle pain, slower recovery and more frequent illness.

• Muscle weakness and less force than usual
• Vague muscle and joint pain
• Slower recovery after hard sessions
• More colds in winter
• Low mood or little energy

None of these complaints proves a deficiency on its own. Only a blood value completes the picture.

Which blood value measures vitamin D?

For your vitamin D status you measure 25-OH vitamin D in your blood, the form that reflects your store over weeks. Reference values differ, and that is where the debate sits. The Dutch Health Council uses a lower threshold than many sports doctors.

Measure your vitamin D value ideally at the end of winter, your lowest point of the year. The Dutch National Institute for Public Health notes the population status is then at its lowest.

What does vitamin D do for your performance and testosterone?

Vitamin D plays a role in your muscle function and immune system, and possibly in your hormone balance. A review in Sports Medicine describes how vitamin D may be relevant for muscle strength in athletes (Owens, 2018). On the link with testosterone the evidence is weaker, and you should not expect a hormone boost from a supplement if your value is already fine.

So see vitamin D as a foundation, not a performance pill. This article is a spoke of our guide vitamins and minerals for athletes, where we set all the core values side by side.

What do you do about a deficiency?

With a proven deficiency you can raise your status with more daylight and, after advice, a supplement. The Dutch Health Council advises extra vitamin D as standard for certain groups. Retest after a few months to see whether your approach works.

If you want a broader look at your hormone balance, also read zinc and testosterone, or compose a panel with the 360 Health blood test.

Vitamin D from sun, food and supplements

Your body gets vitamin D from three sources: sunlight on your skin, a small part from food, and possibly a supplement. In summer a short period outside with uncovered skin is often enough to keep your production going. In winter that route largely falls away in the Netherlands.

Oily fish such as salmon and mackerel supplies vitamin D, and in the Netherlands it is added to margarine and cooking fats. Even so, it is hard to correct a low status with food alone, because the amounts are limited.

That is why many people choose a supplement in winter, certainly when a measurement shows a deficiency. Stick to the advised dose and do not push your value unnecessarily high. If in doubt about the right dose, discuss it with your GP or a sports doctor.

Remember that more sun does not always mean more vitamin D once you are saturated. The body regulates production, and building your store takes weeks, not days.

References

1. Owens DJ, Allison R, Close GL. Vitamin D and the Athlete: Current Perspectives and New Challenges. Sports Medicine. 2018;48(Suppl 1):3-16. PMID: 29368183.
2. Gezondheidsraad. Dietary reference values for vitamin D. Accessed 2026.
3. RIVM. Vitamin D status in the Dutch population. Accessed 2026.

Disclaimer

Every blood test result includes a professional assessment by a BIG-registered doctor. This article gives general information and is not a substitute for medical advice. A blood test is a tool to walk into the conversation with your GP better informed, not a diagnosis in itself. For treatment decisions, discuss your results with your GP.