Does vitamin D affect immunity and winter tone?

Winter often brings more colds, a depressed mood, and a lack of energy. One possible cause is a deficiency in vitamin D, the “sunshine vitamin.” Although the body synthesizes it when exposed to sunlight, it is much more difficult to do so in winter, making this topic particularly relevant.

What is vitamin D?

Vitamin D is a fat-soluble vitamin that plays a key role in the body. It:

• Regulates the absorption of calcium and phosphorus;
• Strengthens bones and muscles;
• It has a strong influence on the immune system;
• It acts as a hormone, controlling the expression of multiple genes.

Effect of vitamin D on the immune system

• Stimulates innate immunity – activates white blood cells (macrophages, monocytes), which protect against viruses and bacteria;
• Modulates adaptive immunity – balances T- and B-lymphocytes, preventing excessive inflammatory reactions;
• Reduces the risk of respiratory infections – adequate levels of vitamin D are associated with a lower incidence of colds, flu, and bronchitis.

Vitamin D and winter tone

During the cold months, many people feel tired and lethargic. This is often associated with seasonal affective disorder (SAD) , in which the lack of light reduces the production of serotonin, the feel-good hormone. Vitamin D helps synthesize neurotransmitters and maintain brain function, thus contributing to emotional balance during the winter.

Why is vitamin D deficiency more common in winter?

• Reduced sunlight – from October to March, UVB rays are not sufficient for synthesis;
• Staying indoors longer – the cold and short days limit sun exposure;
• Food is a poor source – it is mainly found in fish, eggs and dairy products, which rarely cover the needs.

Symptoms of vitamin D deficiency

• Frequent fatigue and weakness;
• Recurrent infections;
• Muscle and bone pain;
• Bad mood and depressive states;
• Delayed recovery after illness.

How to maintain optimal vitamin D levels in winter?

1. Vitamin D supplements – recommended in case of established deficiency or increased risk;
2. Food sources – fatty fish (salmon, mackerel, sardines), eggs and fortified dairy products;
3. Outdoor walks – even winter light has a positive effect;
4. Regular tests – checking 25(OH)D levels in the blood.

Conclusion

Vitamin D is essential for immunity, energy, and mood, especially in the winter. A deficiency can lead to more frequent infections and decreased tone. Maintaining optimal levels through diet, supplements, and reasonable sun exposure is the key to good health and vitality.

© 2025 – Information is for educational purposes only. Consult a doctor if necessary.