Vitamin D plays a crucial role in the immune system, acting more like a hormone than a traditional vitamin. Below is a summary of its function, the consequences of its deficiency, and recommendations for maintaining adequate levels.
Immunological Functions of Vitamin D
Vitamin D influences the immune system in several ways:
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Maintaining the intestinal barrier: It strengthens the junctions between intestinal cells, preventing external agents from entering the bloodstream.
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Stimulation of the innate immune system: It activates macrophages and dendritic cells, which are the first responders to infections.
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Modulation of the adaptive immune system: It promotes the production of Th2 lymphocytes, helping control inflammation.
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Production of antimicrobial agents: It enhances the synthesis of substances that eliminate pathogens.
Additionally, adequate levels of vitamin D have been associated with a reduced risk of acute respiratory infections.
Sources of Vitamin D
There are two main forms of vitamin D:
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Vitamin D2 (ergocalciferol): Found in some vegetables and fungi.
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Vitamin D3 (cholecalciferol): Produced in the skin through sun exposure and present in animal-based foods.
Vitamin D3 is more effective than D2 in raising and maintaining blood levels of vitamin D.
Consequences of Vitamin D Deficiency
A deficiency in vitamin D can weaken the immune system and increase susceptibility to infections. Common causes include:
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Insufficient sun exposure: Particularly in winter or among individuals who spend little time outdoors.
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Vitamin D-poor diet: Especially diets lacking fatty fish, egg yolk, or fortified foods.
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Absorption problems: Certain medical conditions can hinder the absorption of vitamin D.
Severe deficiency can lead to bone diseases such as osteomalacia in adults and rickets in children.
Supplementation Recommendations
To maintain optimal vitamin D levels, it is recommended to:
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Get moderate sun exposure: About 10–15 minutes per day on the face and arms.
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Follow a balanced diet: Include foods rich in vitamin D.
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Take supplements: In cases of deficiency or risk, under medical supervision.
It’s important not to exceed the recommended doses, as excess vitamin D can have adverse effects.
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Bibliography
- Aranow C. Vitamin D and the immune system. J Investig Med. 2011;59(6):881–6. https://pmc.ncbi.nlm.nih.gov/articles/PMC3166406/
- Grant WB, Lahore H, McDonnell SL, et al. Evidence that Vitamin D Supplementation Could Reduce Risk of Influenza and COVID-19 Infections and Deaths. Nutrients. 2020;12(4):988. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7231123/
- Holick MF. Vitamin D deficiency. N Engl J Med. 2007;357(3):266–81. https://www.nejm.org/doi/full/10.1056/NEJMra070553
- Martineau AR, Jolliffe DA, Hooper RL, et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ. 2017;356:i6583. https://www.bmj.com/content/356/bmj.i6583
- Bouillon R, Marcocci C, Carmeliet G, et al. Skeletal and extraskeletal actions of vitamin D: current evidence and outstanding questions. Endocr Rev. 2019;40(4):1109–51. https://academic.oup.com/edrv/article/40/4/1109/5485250
