Methods: We used standard Cochrane systematic review methodology. We searched MEDLINE, EMBASE, the Cochrane Library and KoreaMed to February 28, 2015. We put no restrictions on language or year of publication in our search. Two reviewers completed in duplicate and independently study selection, data abstraction, and assessment of risk of bias. We selected the studies about the current 25-hydrohyvitamin D (25OHD) levels and the prevalence of the current AR, and the other was about the 25OHD levels of cold blood or previously sampled serum and the development of AR.
Results: We selected 10 cross-sectional studies about the current 25OHD levels and the prevalence of the current AR and 6 prospective studies about the development of AR relating with the previous 25OHD levels. Meta-analysis was performed to pool odd ratios from 10 cross-sectional studies (n=42,925) (odd ratio [OR] = 0.95 [0.76-1.20] for top vs. bottom category of 25OHD) and 6 prospective studies (n=22,184) (OR = 0.89 [0.70-1.15] for top vs. bottom category of 25OHD). The prospective studies analyzed additionally with adjusting of the general epidemiologic characteristics. Meta-analysis was performed to pool adjusted odd ratios (AOR) from 6 prospective studies (n=22,184) (AOR = 0.92 [0.64-1.33] for top vs. bottom category of 25OHD).
Discussion: Available evidence from this meta-analysis suggests that the 25OHD level may not relate with neither the prevalence of the current AR nor the development of AR. Since these studies were very heterogeneous and the retrospective or the observational cohort studies, large randomized controlled trials are needed to determine whether vitamin D supplementation may be beneficial in the prevention of AR.