Vitamin D during winter in athletes – risks and recommendations
Did you know that up to 90% of football players experience significant drops in vitamin D levels during the winter? This decline is not just a clinical detail — it is directly linked to a higher risk of injury, fatigue, and reduced performance. We analyse the recommendations of experts Adolfo Muñoz (RCD Mallorca) and Cristian Petri (ACF Fiorentina). Why does this happen, and how is it managed at the elite level in European football?
Vitamin D and its importance in high-performance sport
Vitamin D is an essential nutrient that also acts as a hormone in the body. It plays a key role in calcium absorption, bone health, and the proper functioning of the muscular and immune systems.
In football, maintaining adequate levels is not just a matter of general health, but a factor that can directly influence performance, recovery, and player availability throughout the season.
Drop in vitamin D levels during winter in athletes
Dr. Adolfo Muñoz highlighted in a study conducted between Sevilla FC and Real Betis that players showed a significant decline in vitamin D levels between autumn and February.
- Key insight: Many players move from optimal levels to below 30 ng/ml during winter, affecting muscle function and calcium regulation.
How does this affect performance during the winter months?
Low vitamin D levels do not only impact health, but also athletic performance. During the winter months, they have been associated with:
- Increased risk of muscle injuries
- Poorer recovery between matches
- Higher accumulated fatigue
- Increased incidence of respiratory infections
These factors are especially critical during periods of high competitive load, where small deficits can make a difference in player availability.
Why do vitamin D levels decrease during winter?
Environmental and geographical factors
From the angle of the sun to reduced daylight hours and increased cloud coverage, multiple factors limit exposure to UVB radiation, which is necessary for vitamin D synthesis.
Changes in lifestyle
In Europe, it is common to spend less time outdoors during colder months. Cold weather and rain encourage indoor training, and when athletes go outside, winter clothing limits skin exposure to sunlight.
Physiological and dietary limitations
Although the body stores vitamin D in the liver and fat tissue during summer, these reserves gradually decrease and reach their lowest levels towards the end of winter.
Additionally, it is difficult to meet requirements through diet alone. The main sources are fatty fish, egg yolk, and some mushrooms, which means that in many cases supplementation becomes necessary.
Risk factors and vulnerable populations
Skin pigmentation and cutaneous synthesis
A key factor is the influence of melanin. Higher skin pigmentation acts as a natural barrier against UVB radiation, meaning that players with darker skin tones have a higher risk of vitamin D insufficiency.
This makes individualised blood monitoring essential, especially during the winter months.
Vitamin D supplementation protocols in professional football
Cristian Petri explains how this issue is managed at ACF Fiorentina:
- Daily dose: Supplementation between 2,000 and 4,000 IU depending on blood test results.
- Adherence: Integrating supplementation into daily routines such as breakfast or lunch to ensure consistency.
This approach aims to maintain stable levels over time, avoiding less sustainable strategies such as large weekly doses.
Is vitamin D3 the best supplementation option?
Although different forms of supplementation exist, such as vitamin D2 (plant-based) and D3 (cholecalciferol), professional football protocols prioritise D3 due to its greater effectiveness.
Vitamin D3 is the body’s natural form
Most of the vitamin D we naturally produce (around 80%) through sun exposure is D3, making it easier for the body to recognise and utilise.
Greater stability in the bloodstream
Vitamin D2 acts like a fast-burning fuel, whereas D3 is more stable. It binds more effectively to transport proteins in the blood, allowing levels to remain higher and more stable over time.
More effective at increasing vitamin D levels
Research by Owens and Close has shown that D3 is more effective than D2 at raising vitamin D levels in the body, which is key when a rapid correction of deficiency is required.
Supports muscular performance and immunity
D3 ensures there is enough “raw material” for proper muscle function and a strong immune system. This is crucial to avoid typical February muscle injuries or illnesses that can sideline players at key moments in the season.
The role of the nutritionist in modern football
In modern football, vitamin D management is part of a multidisciplinary approach where nutritionists and medical staff work together to monitor blood markers, adjust diet, and manage supplementation.
This monitoring allows practitioners to anticipate winter-related declines and keep players in optimal condition throughout the season.
Winter is not just a change in the calendar — it is a critical period that can influence performance if not properly managed. Monitoring, prevention, and timely intervention make the difference at the elite level.
If you want to learn how to apply these protocols in professional football, explore our Football Nutrition Master’s Programme.
