Did you know that 80% of French people are vitamin D deficient? And that this massive deficiency has a direct impact on our collective immunity? Also discover our article on renforcer son immunité naturellement.
Vitamin D isn’t just a simple vitamin. It’s a true hormone that influences hundreds of genes, many of which are linked to our immune system.
In this article, we’re going to see why vitamin D is so crucial for your defenses, how to know if you’re lacking it, and how to effectively correct a deficiency.
The role of vitamin D in immunity
A hormone more than a vitamin
Vitamin D is actually a pro-hormone. Once activated in the liver and then the kidneys, it binds to receptors present in almost all cells of your body – including immune cells.
Vitamin D receptors have been found on:
- T and B lymphocytes
- Macrophages
- Dendritic cells
- Epithelial cells of mucous membranes
This means that vitamin D directly influences immune function.
Its actions on immunity
1. Activation of T lymphocytes
T lymphocytes are your immune « soldiers. » Without vitamin D, they remain dormant and cannot activate to fight infections. Studies show that T lymphocytes deficient in vitamin D are unable to respond correctly to pathogens.
2. Production of antimicrobial peptides
Vitamin D stimulates the production of cathelicidins and defensins, molecules that directly kill bacteria and viruses. It’s your internal « natural antibiotic. »
3. Modulation of inflammation
Vitamin D helps maintain a balanced inflammatory response: strong enough to fight infections, but not excessive (which causes damage from autoimmune diseases or severe forms of infections).
4. Strengthening barriers
Vitamin D maintains the integrity of your mucous membranes (intestines, lungs, respiratory tract), your first line of defense against pathogens.
Why are we all deficient?
The natural source: the sun
Normally, your skin synthesizes vitamin D under the effect of the sun’s UVB rays. But several factors make this insufficient:
- Latitude: in France, UVB rays are insufficient from October to April
- Lifestyle: we spend 90% of our time indoors
- Sunscreen: SPF 30 blocks 97% of synthesis
- Age: synthesis capacity decreases with age
- Dark skin: melanin reduces synthesis
- Pollution: filters UVB rays
Diet alone isn’t enough
Very few foods contain vitamin D:
- Fatty fish (salmon, mackerel, sardines)
- Egg yolk
- Liver
- Mushrooms (exposed to UV)
Even with an optimal diet, it’s nearly impossible to reach the recommended intake through food alone.
Signs of Vitamin D Deficiency
Vitamin D deficiency is often silent. But certain signs should alert you:
- Persistent fatigue even after rest
- Recurring infections (colds, flu, stomach bugs…)
- Bone and muscle pain throughout the body
- Depressive mood, especially in winter
- Slow wound healing
- Hair loss
- Muscle weakness
Blood Test Dosage
The only way to know your status precisely: a blood test measuring 25(OH)D.
| Level (ng/mL) | Interpretation |
|---|---|
| < 10 | Severe deficiency |
| 10-20 | Deficiency |
| 20-30 | Insufficiency |
| 30-50 | Adequate level |
| 50-80 | Optimal |
| > 100 | Excess (rare with oral supplementation) |
Goal: aim for a level between 40 and 60 ng/mL for optimal immune function.
« `htmlHow to supplement well
« `D3 or D2?
Always prioritize vitamin D3 (cholecalciferol). D2 (ergocalciferol) is less effective at raising blood levels and has a shorter half-life.
What dosage?
| Situation | Daily dosage |
|---|---|
| Maintenance (normal levels) | 1000-2000 IU/day |
| Insufficiency (20-30 ng/mL) | 2000-4000 IU/day |
| Deficiency (< 20 ng/mL) | 4000-5000 IU/day (under monitoring) |
| Elderly/obese person | Increased needs: 3000-4000 IU/day |
Note: high dosages (> 4000 IU) ideally require blood monitoring.
Daily or weekly?
The daily dose is preferable. It maintains more stable levels than weekly or monthly high-dose intakes.
With or without fat?
Vitamin D is fat-soluble. Take it during a meal containing fats to optimize absorption (up to 50% difference!).
How long does it take to correct a deficiency?
Count on 2 to 3 months of proper supplementation to significantly boost your levels. A blood test after 3 months allows you to adjust the dosage.
Vitamin D and COVID: what we know
Many studies have examined the link between vitamin D and COVID-19. Here’s what we can say:
- People who are deficient have a higher risk of severe forms
- Preventive supplementation seems to reduce the risk of infection
- Correcting a deficiency before infection improves the prognosis
It’s not a miracle treatment, but maintaining good vitamin D status is part of an overall immune support strategy.
Recommended Supplements
Vitamin D3
High-quality D3 form for effective supplementation. Essential from October to April to maintain adequate levels.
Liposomal Vitamin C
Ideal partner for vitamin D for immunity. The two vitamins work in synergy.
Discover Novoma Liposomal Vitamin C
Zinc Bisglycinate
The trio D + C + Zinc forms a powerful combination to strengthen natural defenses.
Discover Novoma Zinc Bisglycinate
Omega 3 Epax
Omega 3s enhance the action of vitamin D and have their own immunomodulatory effects.
Discover Novoma’s Omega 3 Epax
Great deal: use code SATYVO10 to get 10% off on your Novoma order!
Frequently Asked Questions
Can you have too much vitamin D?
Vitamin D intoxication is rare and only occurs with very high doses (> 10,000 IU/day) over a long period. Usual dosages (1,000-4,000 IU) are perfectly safe. An occasional blood test allows you to check that you’re staying within the normal range.
Should you supplement in summer?
If you regularly expose yourself to the sun (15-20 min at the end of the morning, arms and legs uncovered, without sunscreen), you can reduce or stop supplementation from May to September. Otherwise, continue at a reduced dose (1000 IU).
Vitamin D and calcium: should you take them together?
Vitamin D improves calcium absorption, but it’s not necessary to take them together if your diet provides enough calcium. On the other hand, if you’re supplementing with calcium, vitamin D is essential for its utilization.
My doctor prescribed me one ampoule per month, is that okay?
High-dose ampoules (100,000 IU) are convenient but less physiological than a daily intake. Studies show that daily doses maintain more stable levels. If possible, prefer daily supplementation.
Conclusion
Vitamin D is a pillar of immunity too often overlooked. With 80% of the population deficient, it’s likely the most universally necessary supplement.
The essential points:
- Vitamin D directly activates immune cells
- Deficiency is nearly universal in France
- Prioritize D3 form, taken daily with fat
- Aim for a blood level of 40-60 ng/mL
- Supplementation recommended from October to April minimum
A simple gesture that can make a real difference for your immunity and overall health.
This article is for informational purposes and does not replace medical advice. If you have any doubt about your vitamin D status, ask your doctor for a blood test.