Null association between serum 25-hydroxyvitamin D levels with allergic rhinitis, allergic sensitization and non-allergic rhinitis: A Mendelian randomization study

Allergic rhinitis and allergic sensitization are the most common and prevalent allergic conditions in the world. It has been suggested that serum 25-hydroxyvitamin D might have a role in immunomodulation and, consequently, in allergic rhinitis and allergic sensitization. This study aimed to assess a causal association between 25-hydroxyvitamin D levels and risk of allergic rhinitis or allergic sensitization, using two-sample Mendelian randomization (MR) approach.

Instrumental variables identified seven single nucleotide polymorphisms (SNPs) associated with serum 25-hydroxyvitamin D levels. The primary objective was allergic rhinitis, and the secondary objectives were allergic sensitization and non-allergic rhinitis. Two cohort studies provided the genome-wide association summary statistics of the outcomes. MR analysis with a random-effects inverse variance weighted method was performed as the primary analysis to estimate the overall effect size. Sensitivity analysis using the weighted median method and MR-Egger regression method was conducted. A subgroup analysis based on 25-hydroxyvitamin D synthesis-SNPs was also applied.

There wasn’t a causal association between serum 25-hydroxyvitamin D and risk of allergic rhinitis, and subgroup analysis also showed no relation between 25-hydroxyvitamin D synthesis-related SNPs and outcomes. The same results were obtained for sensitivity analysis.

In conclusion, this study did not find any evidence that supports a causal association between serum 25-hydroxyvitamin D levels and risk of allergic rhinitis, allergic sensitization, or non-allergic rhinitis in the European-ancestry population. This conclusion is against the use of vitamin D supplementation for the prevention of allergic diseases.