Evidence check: MTHFR in the context of allergy

The claim that an MTHFR variant directly affects allergy risk is not well supported by evidence. MTHFR (methylenetetrahydrofolate reductase) is a key enzyme in folate and homocysteine metabolism. Some observational studies have found weak associations between certain MTHFR polymorphisms (e.g., rs1801133, C677T) and allergic conditions like asthma or atopic dermatitis, but the effects are small, inconsistent, and often not replicated. The proposed mechanism (elevated homocysteine → oxidative stress → immune modulation) remains speculative. Consumer DNA tests tend to overstate such links, presenting them as direct risk predictors. In reality, allergy risk is polygenic (involving HLA, IL-4, IL-13, etc.) and heavily influenced by environment. A single MTHFR SNP has little clinical utility. Evidence grade: unclear/mixed. Caveat: Do not change diet or supplement based solely on this gene; assess folate and B12 status via blood tests instead.