Vitamin D: how it influences immunity, mood, and sleep. What is the right level?

Various studies and specialists in nutrition and preventive medicine agree: up to 80% of the population may have a vitamin D3 deficiency without realising it. Known as the “sun vitamin”, this molecule plays a fundamental role in multiple biological processes—from immunity to mood and gut health.

  1. What does vitamin D3 do in the body?
    Health experts explain that vitamin D3 functions as a master regulator, influencing key processes such as:

  • Cellular immunity, supporting T-lymphocyte activity

  • General wellbeing and mental focus

  • The metabolism of calcium, phosphorus and glucose

  • The integrity of the intestinal barrier

  1. Parasites: silent enemies of vitamin D
    Infectious-disease physicians note that the presence of parasites can be a frequent cause of vitamin D deficiency. Although they often go unnoticed in routine tests, symptoms such as itching, recurrent infections, low appetite or strong sweet cravings may point to their presence. These organisms can also reduce zinc and ferritin levels, weakening the immune system.

  2. How to supplement vitamin D3 intelligently
    Most specialists advise measuring vitamin D levels before starting any supplementation. The recommended “optimal” range is cited as 60–80 ng/mL, well above the standard values of 20–30 ng/mL that often appear in reports. Supplementation is typically taken as drops or capsules, with levels rechecked every 3–6 months. Common daily doses range from 2,000 to 4,000 IU, with a suggested safe maximum of 10,000 IU.

  3. Natural source: the sun—without filters
    Dermatologists and nutritionists often indicate that moderate sun exposure—around 30 minutes daily without sunscreen—can significantly raise vitamin D3 levels. It’s important not to cover all the skin, especially in summer. While sunscreens protect the skin, they also block vitamin D synthesis.

  4. Microbiota, fibre and diet: immunity from within
    Nutrition specialists emphasise that a balanced gut microbiota depends on a high-fibre diet (soluble and insoluble), the main fuel for beneficial bacteria. Excess ultra-processed foods, chronic stress and high sugar intake disrupt the microbiota, weaken immunity and increase inflammation.

  5. Vitamin D3 works better with vitamin K2 MK-7
    Medical research is said to confirm that combining vitamin D3 with vitamin K2 (MK-7) helps prevent calcium build-up in the arteries and supports correct deposition in bones. It’s advisable to obtain calcium and magnesium from natural foods such as spinach, broccoli or celery.

  6. A holistic approach to health
    Practitioners of functional medicine remind us that the body is an interconnected system, where one imbalance can affect many areas. It is therefore essential to pay attention to:

  • Optimal vitamin D3 and ferritin levels

  • Detection and removal of parasites

  • Microbiota health and a fibre-rich diet

  • Adequate sun exposure

  • Individualised supplementation according to needs

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