Vitamin D is often known as the “sunshine vitamin” for its role in supporting bone health and helping our bodies absorb calcium. But over the last decade, researchers have uncovered another important role for vitamin D—its impact on the immune system. In particular, its potential influence on allergic diseases such as eczema (atopic dermatitis), hay fever (allergic rhinitis), asthma, and food allergies is becoming increasingly clear.
A recent review article published in Frontiers in Immunology (Zhang et al., 2024) explores this connection in depth, summarising the latest scientific findings on how vitamin D affects immune responses and allergic conditions.
Understanding Vitamin D and the Immune System
Vitamin D affects both the innate and adaptive branches of the immune system, which are responsible for our body’s first-line defence and long-term immune responses, respectively. Immune cells such as T cells, B cells, macrophages, and dendritic cells all have vitamin D receptors. This means that vitamin D can influence how these cells behave—helping to calm down inflammation, promote immune tolerance, and reduce the likelihood of overreacting to harmless substances like pollen, pet dander, or certain foods.
Vitamin D and Atopic Dermatitis (Eczema)
Multiple studies reviewed in the article found that low vitamin D levels are commonly associated with more severe atopic dermatitis symptoms. In both children and adults, vitamin D supplementation has been shown to reduce the severity of eczema, leading to improved skin health and quality of life. One study found that every unit increase in vitamin D was linked to a measurable reduction in eczema severity scores.
Vitamin D and Allergic Rhinitis (Hay Fever)
Allergic rhinitis—marked by sneezing, nasal congestion, and itchy eyes—has also been linked to low vitamin D levels. Research suggests that people with hay fever often have lower levels of vitamin D compared to healthy individuals. Vitamin D may help restore balance in the immune system by influencing T-helper cells (particularly shifting from an allergic Th2 response to a more balanced state). Supplementing with vitamin D alongside standard treatment (such as nasal sprays) may further reduce symptoms and inflammation.
Interestingly, maternal vitamin D levels during pregnancy also appear to impact children’s risk of developing allergic rhinitis later in life.
Vitamin D and Asthma
Asthma, especially allergic asthma, involves chronic inflammation of the airways. Several studies in the review support a link between low vitamin D and worse asthma outcomes, including more frequent asthma attacks and reduced lung function. Supplementing with vitamin D has been shown to improve asthma control, reduce the need for corticosteroids, and decrease the risk of hospital visits in some patient groups.
Vitamin D may also protect against the airway remodelling seen in chronic asthma and may reduce inflammation by influencing a range of immune cells and pathways.
Vitamin D and Food Allergies
Emerging research indicates a potential connection between vitamin D levels and food allergies, particularly in infants and young children. For example, babies born during months with less sunlight exposure have been shown to have a higher risk of food allergies. One large Australian study found that vitamin D deficiency was linked to a significantly higher risk of peanut and egg allergy in infants. While not all studies agree, the majority suggest that both maternal and early-life vitamin D levels may play a role in allergy development.
Can Vitamin D Supplementation Help?
The review highlights that supplementing with vitamin D may improve outcomes in people with allergic diseases. Clinical trials have shown benefits in reducing symptoms of asthma, eczema, allergic rhinitis, and chronic urticaria (hives). Some studies also suggest that vitamin D can improve the effectiveness of allergen immunotherapy (also known as desensitisation treatment), possibly by promoting immune tolerance.
However, the authors caution that more high-quality research is needed. The ideal dose, duration, and timing of vitamin D supplementation—especially in different populations and allergy types—are not yet fully established.
Conclusion
This comprehensive review confirms that vitamin D is more than just a bone-health nutrient—it plays a critical role in regulating our immune system and potentially reducing allergic disease severity. While not a cure, maintaining adequate vitamin D levels may be a helpful part of a broader treatment strategy for people living with allergies.
Patients are encouraged to speak to their healthcare provider before starting any supplement, especially if they have allergies or are pregnant. A simple blood test can assess vitamin D levels, and supplementation may be considered based on individual needs.
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