Vitamin D in Spring: When You Can Adjust Your Supplementation

Winter is fading, days are getting longer, and the sun is showing itself more frequently again – a welcome change for body and mind, especially for physically active people. With spring, however, many who supplemented with vitamin D during the darker months face the question: When and how should I adjust my vitamin D intake? This guide highlights the importance of vitamin D for athletes, the role of the sun in spring, and provides practical recommendations for adequate supplementation in 2026.

Why Vitamin D is Important for Athletes

Vitamin D, often called the “sunshine vitamin,” is, strictly speaking, not a vitamin in the classical sense but a prohormone. It plays a central role in numerous bodily functions that are crucial for athletes.

What is Vitamin D and Why is it Relevant for Physically Active People?

Vitamin D exists in two main forms: Vitamin D2 (ergocalciferol) and Vitamin D3 (cholecalciferol). The most important form for humans is Vitamin D3, which our body primarily produces itself when exposed to sunlight. Only a small part of the requirement is covered by food.

For athletes, an adequate supply of vitamin D is particularly important, as it influences various processes in the body that are directly related to performance, regeneration, and health. Studies show that the vitamin D status in athletes is often worse than one might assume given their frequent outdoor activities. A systematic review and meta-analysis from 2022 estimated the insufficiency in adult elite athletes at around 30 percent. For indoor athletes, in winter, and in northern latitudes, the numbers are even higher.

How it Works / How the Body Can Benefit

Vitamin D has a broad spectrum of action in the body and can support your training and health in various ways:

• Bone Health: Vitamin D is essential for the absorption of calcium and phosphate from the intestine and their incorporation into bones. This contributes to the maintenance of normal bones and can reduce the risk of stress fractures, which can occur during intense training.
• Muscle Function and Strength: It influences muscle contraction, muscle strength, and muscle coordination. Optimal vitamin D levels can improve muscle strength and reduce the risk of muscle damage and weakness. It also plays a role in muscle protein synthesis, which can positively impact muscle growth and regeneration.
• Immune System: Vitamin D contributes to the normal function of the immune system and can reduce susceptibility to infections, especially of the upper respiratory tract. For athletes with high training loads, a strong immune system is crucial to avoid training interruptions due to illness.
• Regeneration: A stable vitamin D status can shorten regeneration after micro-injuries and improve resilience.
• Cardiovascular Fitness: Recent studies suggest that high vitamin D levels may be associated with significantly higher cardiorespiratory fitness (aerobic endurance).
• Mood and Mental Performance: There is evidence that vitamin D can positively influence mood and mental performance.

Recommended Amounts / Dosage

The German Nutrition Society (DGE) estimates the daily requirement for vitamin D, in the absence of endogenous production, to be 20 micrograms (µg) for all age groups from the first year of life. This corresponds to 800 International Units (IU).

For athletes, however, the requirement may be higher. Some experts recommend that athletes aim for a 25(OH)D level above 40 ng/ml, which can be achieved by taking 4000 to 10000 IU of vitamin D per day, depending on factors such as size and skin color. Although 1,000 IU are traditionally recommended in Europe, guidelines in the USA are often between 2,000 and 4,000 IU. For most athletes, 1,000 IU daily may be sufficient; in winter months or during high stress, an increase to 2,000 IU daily may be advisable.

It is important that vitamin D is fat-soluble and should therefore ideally be taken with a meal containing healthy fats to optimize absorption. Many experts also recommend the simultaneous intake of vitamin K2 to optimize calcium utilization in the body and minimize the risk of vitamin D supplementation alone.

Best Natural Sources (Foods, Examples)

Although the body's own production through sunlight is the main source of vitamin D, you can also support your vitamin D balance through diet. However, the vitamin D content in most foods is relatively low.

The best natural food sources of vitamin D include:

• Fatty Fish: Salmon, herring, mackerel, sardines, tuna, and eel are particularly rich in vitamin D3. For example, a 100-gram serving of cooked salmon can provide approximately 526 IU of vitamin D, mackerel about 643 IU, and sardines around 272 IU.
• Cod Liver Oil: A classic supplement that contains high amounts of vitamin D.
• Mushrooms: Certain mushroom varieties like shiitake, maitake, chanterelles, button mushrooms, porcini, and slippery jacks can produce vitamin D2 when exposed to sunlight or UV light.
• Egg Yolk: Also contains vitamin D, but in significantly smaller amounts than fatty fish. To achieve comparable levels, you would need to eat a large quantity of egg yolks.
• Fortified Foods: Some foods such as milk, plant-based dairy products, juices, and breakfast cereals are fortified with vitamin D to improve supply.

It is important to note that it is difficult to meet your entire vitamin D requirements through diet alone.

When are supplements useful?

Vitamin D supplements are useful when the body's own production from sunlight is insufficient and requirements cannot be met through diet. In Central Europe, this is particularly the case during the months of October to March, as the sun's angle of incidence is too low to stimulate sufficient UVB synthesis in the skin.

Supplementation may still be appropriate in spring, especially if you spend a lot of time indoors, use sunscreen (which blocks UVB radiation), have darker skin pigmentation, or are older, as the skin's synthesis capacity decreases. Athletes who primarily train indoors are also more susceptible to vitamin D deficiency. A blood test by a doctor can clarify your current vitamin D levels and is the best basis for an individual dosage recommendation.

Possible Risks / Overdose / Interactions

While adequate vitamin D supply is essential, excessive intake, particularly through high-dose supplements, can pose health risks. An overdose solely from sun exposure is extremely unlikely, as the body stops production when enough vitamin D is present.

Vitamin D overdose, also known as hypervitaminosis D, can lead to elevated calcium levels in the blood (hypercalcemia), which in turn can cause various symptoms, including fatigue, muscle weakness, heart rhythm disturbances, and, in the worst case, kidney damage.

The German Federal Institute for Risk Assessment (BfR) recommends a maximum of no more than 20 µg (800 IU) of vitamin D per daily dose in food supplements to avoid long-term health risks. Higher-dosed preparations exceeding 20 µg per day are classified as medicinal products. A daily intake of 100 micrograms can already be an overdose, according to the BfR's assessment.

It is also important to consider possible interactions with medications. Individuals taking oral anticoagulants of the coumarin type (vitamin K antagonists) should seek medical advice before taking vitamin D supplements, especially in combination with vitamin K.

The European Food Safety Authority (EFSA) has set a safe upper limit of 4000 IU (100 µg) per day for adolescents and adults. In 2026, binding maximum levels for nutrients in food supplements, including vitamin D, are expected to be set across the EU. This is intended to lead to reformulation and market cleansing, and mean the end of high-dose products without risk assessment.

The Role of the Sun in Vitamin D Production in Spring

With the arrival of spring, the sun regains its strength, and with it, the natural vitamin D production in your skin. But when exactly is the sun sufficient, and what factors play a role?

Your body produces vitamin D3 when UVB rays hit your skin, converting a precursor of vitamin D into the active vitamin. This endogenous production is the primary source of vitamin D, covering about 80–90% of your needs.

From October to March, solar radiation in Germany and other temperate climate countries is generally not strong enough, as the angle of incidence of UVB rays is too flat to allow for significant vitamin D synthesis. Even if the spring sun feels warm, the intensity of UVB radiation is often still insufficient. A rule of thumb states: If your shadow is longer than your height, no significant vitamin D production occurs, as the sun's elevation angle above the horizon must be at least 42 degrees.

In spring, as the days get longer and the sun rises higher, your body can increasingly produce vitamin D itself. To achieve an adequate supply, current knowledge suggests exposing your face, hands, and arms to the sun uncovered for about 5 to 25 minutes several times a week, depending on skin type and season. It is important to avoid sunburn.

Various factors influence how much vitamin D your body produces from sunlight:

• Latitude and Season: In northern latitudes, vitamin D production is severely limited during the winter months. In spring, it increases again.
• Time of Day: The most effective time for vitamin D production is around midday when the sun is highest.
• Skin Type: Darker skin types produce significantly less vitamin D than lighter skin types with the same sun exposure, as melanin filters UVB radiation.
• Exposed Skin Area: The more skin exposed to the sun, the more vitamin D can be formed. Face, arms, and hands are often uncovered and offer a good surface.
• Sunscreen: Sunscreen blocks UVB radiation, significantly reducing vitamin D production.
• Age: The skin's ability to synthesize vitamin D decreases with age.

Individual Factors for Adjusting Supplementation

The decision to adjust your vitamin D supplementation in spring should be based on individual factors. There is no blanket recommendation that applies equally to every athlete.

• Your Vitamin D Status: A blood test is the most reliable way to determine your current vitamin D level (25-hydroxyvitamin D). A value below 30 nmol/l is considered a clear deficiency, 30 to 50 nmol/l as insufficiency, and above 50 nmol/l as sufficient. Some experts recommend a target range of 75 to 125 nmol/l for athletes. If your levels are very low at the end of winter, continuing supplementation into spring can be beneficial to replenish stores.
• Training Intensity and Location: If you continue to train intensely, especially indoors, your vitamin D requirements may remain elevated. Outdoor training, on the other hand, can stimulate the body's own production. A 2026 EHU study showed that runners who trained outdoors had similar vitamin D levels to non-runners who supplemented, highlighting the importance of outdoor activities.
• Skin Type and Sun Protection: Darker skin types require longer sun exposure for the same vitamin D production. If you use a lot of sun protection to protect your skin, vitamin D synthesis will also be reduced.
• Geographical Location: The further north you live, the longer it takes in spring for the sun to provide sufficient UVB radiation for vitamin D production.
• Dietary Habits: If your diet contains few vitamin D-rich foods, supplementation may continue to play an important role in spring to ensure an adequate supply.

Possible Signs of an Adjusted Need

Your body can send you subtle signals that might indicate a vitamin D deficiency or an adjusted need. Pay attention to the following signs:

• Persistent fatigue and reduced performance: Despite sufficient sleep and training, you feel tired, sluggish, and unmotivated.
• Frequent infections and prolonged recovery times: Your immune system seems weakened, you are more susceptible to colds or flu-like infections, and recovery takes longer.
• Muscle weakness, muscle pain, or body aches: Vitamin D plays an important role in muscle function. A deficiency can manifest as muscle weakness, diffuse pain, or slowed regeneration.
• Depressed mood, especially during winter months: Although spring is approaching, persistently low mood or even symptoms of "winter depression" can indicate a vitamin D deficiency.
• Worsened sleep quality: A lack of vitamin D can also impair sleep quality.
• Increased risk of stress fractures: If you, as an athlete, frequently suffer from bone problems, this could be an indication of suboptimal vitamin D levels.

These symptoms are often non-specific and can have other causes. Therefore, it is advisable to consult a doctor if symptoms persist and have your vitamin D levels checked.

Practical Tips for Reducing or Adjusting the Dose

As the sun regains strength in spring and you spend more time outdoors, you can gradually adjust your vitamin D supplementation. Here are some practical tips:

1. Blood Test as a Basis: Have your vitamin D levels tested at the beginning of spring. This gives you a clear baseline for your adjustments. If your levels are already sufficient, you can reduce or pause the dose.
2. Gradual Reduction: Instead of abruptly stopping supplementation, you can gradually reduce the dose. For example, if you were taking 4000 IU per day, you could reduce to 2000 IU or 1000 IU and observe the effect.
3. Consciously Use Sunny Days: Spend regular time outdoors, especially around midday when UVB radiation is most intense. Try to expose your face, arms, and hands to the sun for 10–25 minutes without risking sunburn. For athletes, especially outdoor athletes, this can already happen during training.
4. Consider Skin Type: If you have a darker skin type, you may need longer sun exposure or a higher base supplementation to maintain your vitamin D levels.
5. Pay Attention to Your Diet: Incorporate more vitamin D-rich foods into your diet to support natural intake. These include fatty fish like salmon and herring, as well as eggs and certain mushrooms.
6. Check Combination Products: If you are taking a combination product with vitamin D and K2, discuss the adjustment with your doctor or pharmacist.
7. Observe Your Body: Look out for signs of a potential deficiency, such as fatigue or increased susceptibility to infections. Should these symptoms reappear, a renewed adjustment of supplementation might be necessary.
8. Professional Advice: In case of doubt or uncertainty, you should always consult a doctor or a qualified nutritionist. They can help you create an individual plan.

When Continuing Supplementation Can Be Beneficial

Even in spring and summer, vitamin D supplementation can remain beneficial for certain groups of people or under specific circumstances.

• Persistent Vitamin D Deficiency: If your blood test at the beginning of spring shows a significant deficiency (below 30 nmol/l), it is advisable to continue supplementation to replenish stores and reach optimal levels. Your doctor can recommend targeted therapy in this case.
• Low Sun Exposure: If you spend most of your time indoors due to your job or other reasons and get little direct sun on your skin, supplementation may be necessary even in the sunnier months. This applies, for example, to many indoor athletes.
• Regular Use of Sunscreen: If you consistently protect your skin with a high sun protection factor (SPF) to prevent sunburn and skin cancer, vitamin D production is greatly reduced. In this case, year-round supplementation at a moderate dose can be beneficial.
• Dark Skin Type: People with darker skin pigmentation require significantly longer sun exposure to produce the same amount of vitamin D as lighter skin types. An adjustment in supplementation should take this into account.
• Certain Diseases or Medications: In certain pre-existing conditions that affect vitamin D absorption or metabolism, or when taking certain medications, an increased need may exist. Medical consultation is essential here.
• High Training Volume and Regeneration: Competitive athletes with very high training volumes and intense loads may have an increased vitamin D requirement to support regeneration and keep the immune system stable.
• Older Age: With increasing age, the skin's ability to produce vitamin D decreases. Older athletes can therefore benefit from continuous supplementation.

Factor	Influence on Vitamin D Production in Spring	Recommendation for Supplementation
Sun Exposure	Increasing, but dependent on latitude, time of day, skin type, and exposed area.	With regular, unprotected sun exposure (approx. 10-25 min daily around midday), the dose can be reduced or paused. With low exposure: Continue with a moderate dose.
Skin Type	Darker skin types produce less vitamin D.	Darker skin types may require higher doses or longer supplementation.
Sunscreen	Significantly reduces vitamin D production.	With consistent sun protection, year-round supplementation can be beneficial.
Blood Level (current value)	Crucial for individual needs.	In case of deficiency (below 30 nmol/l): Continue supplementation, possibly higher dose in consultation with a doctor. With optimal values: Adjust or pause.
Training Location	Indoor training reduces sun exposure.	Indoor athletes continue to benefit from supplementation. Outdoor athletes may be able to reduce it.
Age	Ability to synthesize vitamin D decreases.	Older athletes can benefit from continuous, adjusted supplementation.
Nutrition	Small contribution to overall needs, but supportive.	A balanced diet with vitamin D-rich foods is always recommended, but rarely replaces supplementation when sun exposure is insufficient.

View current models, prices & ratings directly on Amazon.

Advertisement · As an Amazon Partner, we earn from qualifying purchases. Prices/availability may change.