Vitamin D and immunity: why a deficiency can weaken your natural defenses

More than 80% of the French population has a vitamin D deficiency or insufficiency in winter [1]. However, this vitamin plays a fundamental role in immunity, resistance to respiratory infections, and even the prevention of certain autoimmune diseases. In this article, we analyze what the science says and how to naturally optimize your intake – with products available on Pharmaplusfrance.store.

1. What is vitamin D?

Vitamin D is a fat-soluble vitamin produced in the skin by sunlight (UVB). It is also available through food or supplements.
There are two forms:

• Vitamin D2 (ergocalciferol) – plant-based
• Vitamin D3 (cholecalciferol) – most active and best absorbed form [2]

2. What is its role in immunity?

Vitamin D:

• Stimulates innate immune cells (macrophages, monocytes)
• Strengthens the action of T and B lymphocytes [3]
• Plays a recognized anti-inflammatory and anti-infectious role [4]

👉 A deficiency is associated with an increased risk of respiratory infections, influenza, COVID-19 and bronchitis [5].

3. Vitamin D deficiency: who is affected?

• People with little exposure to the sun (working indoors, winter)
• Dark skin (less skin synthesis)
• Seniors (reduced production with age)
• Vegans (few food sources)
• Children, pregnant women, obese or diabetic people [6]

⚠️ In France, more than 80% of adults have a level < 30 ng/mL in winter [1].

4. Recommended intakes and dosages

• ANSES recommends: 600 to 800 IU/day for adults [7]
• But most studies recommend 1000 to 2000 IU/day for optimal immune effect [4]
• In case of proven deficiency: treatment at 50,000 IU/week or 100,000 IU/month under medical supervision

5. Scientific results

• A meta-analysis of 25 clinical trials showed that vitamin D reduces the risk of respiratory infection by 12 to 30%, particularly in deficient subjects [5]
• Several studies have observed a better prognosis for COVID-19 in patients with sufficient vitamin D levels [6]

6. Practical advice (scientifically validated)

• 🕒 Take vitamin D with a fatty meal for better absorption [8]
• 🌞 Expose yourself to the sun for 15 to 20 minutes a day (excluding hot hours)
• 📆 Do a 25(OH)D blood test if in doubt or if you have a pathology
• ⚠️ Do not exceed 4000 IU/day without medical advice

7. Products available on Pharmaplusfrance.store

• Vitamin D3 1000 IU/day, in oil form, highly assimilable
• Plant-based D3 (from lichen) for vegetarians and vegans
• D3 + K2 complex, to strengthen the skeleton and calcium fixation
• Children's Vitamin D3 (drops), no additives, pediatric dosage

All our products comply with European standards.

Conclusion

Vitamin D is much more than just a bone vitamin. It acts as an immune regulator and can actually reduce seasonal infections if taken in the right dose.
To avoid deficiencies, a sensible supplement, like that offered on Pharmaplusfrance.store, is a reliable and effective solution.

Scientific references

1. Public Health France. Esteban 2019 Study on the Vitamin Status of the Population
2. Tripkovic L et al. Comparison of vitamin D2 and D3 supplementation, Am J Clin Nutr. 2012
3. Aranow C. Vitamin D and the immune system, J Investig Med. 2011
4. Martineau AR et al. Vitamin D supplementation to prevent acute respiratory infections, BMJ. 2017
5. Jolliffe DA et al. Vitamin D and COVID-19: narrative review, BMJ. 2020
6. Lips P. Worldwide status of vitamin D nutrition, J Steroid Biochem Mol Biol. 2010
7. ANSES. Recommended dietary intake of vitamin D, 2012 report
8. Dawson-Hughes B et al. Impact of meal composition on vitamin D absorption, Am J Clin Nutr. 2013

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