Is Vitamin D 25-OH useful for Allergie?

Measuring 25-hydroxyvitamin D (25-OH-D) is the standard method to assess vitamin D status, but it is not a test for allergies per se. Observational studies have linked low vitamin D levels with higher prevalence of allergic conditions such as asthma, eczema, and hay fever. However, the evidence is largely associative; randomized trials of supplementation show mixed results – some suggest modest benefits, others no effect. Therefore, vitamin D cannot be recommended as a diagnostic or therapeutic tool for allergies based on current data. A 25-OH-D test is useful to detect deficiency, which may indirectly support immune regulation. For allergy diagnosis, specific IgE testing or oral food challenges remain the gold standard. Caveat: while deficiency is common, excessive supplementation can lead to toxicity. The evidence for a direct role of vitamin D in allergies is moderate and insufficient for routine clinical application.