Vitamin D Supplementation and Allergic Rhinitis: A Systematic Review and Meta-Analysis

Background and Objectives: Vitamin D supplementation is effective for allergic rhinitis; however, its usefulness is unclear. We conducted a systematic review and meta-analysis to examine the conditions in which vitamin D supplementation was effective in allergic rhinitis management. Materials and Methods: Randomized controlled trials of vitamin D supplementation used for patients with allergic rhinitis were searched for across different databases. We extracted scores on patients' symptoms and the medication types used as the baseline treatments and performed a meta-analysis to evaluate the effect of vitamin D supplementation on allergic rhinitis symptoms. Meta-regression and subgroup analyses were performed for the average age, proportion of female participants, concomitant medications, vitamin D administration durations, and baseline serum 25-hydroxyvitamin D levels. Results: In total, 2389 articles were screened, and 5 randomized controlled trials (RCTs) were included in the meta-analysis. Compared with placebos, vitamin D supplementation alleviated allergic rhinitis symptoms, although the difference was not significant; there was significant heterogeneity among studies (standardized mean difference [SMD] = -2.69, 95% confidence interval [CI]: -6.20 to 0.82, I2 = 98%, p < 0.01). The proportion of female participants in the RCTs (slope: 0.21, p = 0.026) and concomitant corticosteroid use (slope: -9.16, p = 0.005) influenced the vitamin D response. Compared with the placebos, vitamin D supplementation without corticosteroids alleviated the allergic rhinitis symptoms (SMD = -0.56, 95% CI: -0.90 to -0.23). Combination treatment with corticosteroids also non-significantly alleviated symptoms. Additionally, the heterogeneity between studies was significant (SMD = -5.97, 95% CI: -13.55 to 1.16, I2 = 99%, p < 0.01). Conclusions: The study results suggest that vitamin D supplementation alleviates allergic rhinitis symptoms, although the effects differ according to the patient's sex and concomitant medications.