How are Vitamin D 25-OH and Allergie related?

The relationship between vitamin D (25-OH) and allergies has been studied for years, but the evidence remains inconsistent. Some observational studies suggest that low vitamin D levels may be associated with an increased risk of allergic conditions such as asthma, atopic dermatitis, or hay fever. Vitamin D influences the immune system by modulating T-cells and cytokines, which could theoretically dampen allergic responses. However, randomized controlled trials (RCTs) do not show a consistent protective effect from supplementation. In children, some studies have even observed an increased allergy risk with very high vitamin D levels (U-shaped relationship). The evidence is therefore 'human-moderate' to 'mixed'. Importantly, vitamin D deficiency should be corrected, but supplementation solely for allergy prevention is not sufficiently supported. Individual genetic predisposition, environmental factors, and gut health also play a role. If allergies are suspected, medical evaluation is recommended.