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

A large portion of the French population suffers from vitamin D deficiency or insufficiency in winter [1], often without knowing the symptoms (fatigue, recurrent infections, muscle pain). This vitamin plays a fundamental role in immunity and resistance to respiratory infections. In this article, we analyze what science says, which vitamin D3 dosage to choose, 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 under the effect of sunlight (UVB). It is also supplied through diet or supplements.
There are two forms:

• Vitamin D2 (ergocalciferol) – of plant origin
• Vitamin D3 (cholecalciferol) – the 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 documented anti-inflammatory and anti-infective role [4]

👉 A deficiency is associated with an increased risk of respiratory infections [5].

3. Vitamin D deficiency: who is affected?

• People with little sun exposure (indoor work, winter)
• Dark skin (less skin synthesis)
• Seniors (reduced production with age)
• Vegans (few dietary sources)
• Children, pregnant women, obese or diabetic individuals [6]

4. Recommended intake and dosages

• ANSES recommends: 600 to 800 IU/day for adults [7]
• In case of confirmed deficiency, a dosage adjustment may be proposed under medical supervision

5. Scientific results

• A meta-analysis of clinical trials has shown that vitamin D reduces the risk of acute respiratory infection, particularly in deficient subjects [5]

6. Practical tips (scientifically validated)

• 🕒 Take vitamin D with a fatty meal for better absorption [8]
• 🌞 Expose yourself to the sun 15 to 20 min/day (outside of hot hours)
• 📆 Get a 25(OH)D blood test if in doubt or with a pathology
• ⚠️ Respect maximum recommended doses, unless otherwise advised by a doctor

7. Our vitamin D3 supplements on Pharmaplusfrance.store

• Vitamin D-3, Softgels, highly absorbable oil form (NOW Foods)
• Vegetable Vitamin D-3, Capsules (NOW Foods) — for vegetarians and vegans
• Vitamin D-3 & K-2 Complex (NOW Foods) — to strengthen bones and calcium fixation

All our products comply with European standards.

Conclusion

Vitamin D is much more than a vitamin for bones. It participates in immune regulation and can contribute, as part of a global lifestyle, to limiting seasonal infections when deficiency is proven and corrected with appropriate monitoring.
To avoid deficiencies, a reasoned supplementation, such as that offered on Pharmaplusfrance.store, is an option to consider with a healthcare professional.

Scientific references

1. Santé Publique France. Esteban 2019 study on the vitamin status of the population.
2. Tripkovic L et al. Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. Am J Clin Nutr. 2012;95(6):1357-64. (PubMed)
3. Aranow C. Vitamin D and the Immune System. J Investig Med. 2011;59(6):881-6. (PubMed)
4. Martineau AR et al. Vitamin D supplementation to prevent acute respiratory infections. BMJ. 2017;356:i6583. (PubMed)
5. Jolliffe DA et al. Vitamin D and COVID-19: narrative review. BMJ / Lancet Diabetes Endocrinol. 2021-2022.
6. Lips P. Worldwide status of vitamin D nutrition. J Steroid Biochem Mol Biol. 2010.
7. ANSES. Recommended nutritional intakes for 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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