International Journal of Preventive Medicine (Int J Prev Med)2008-7802151120250106111EN1 Food Security Research Center AND Department of Community Nutrition, School of Nutrition and Food Science, Isfahan University of Medical Sciences, Isfahan2 Department of Nutrition, Science and Research Branch, Islamic Azad University, Tehran,3 Research Center for Biochemistry and Nutrition in Metabolic Diseases, Institute for Basic Sciences, Kashan University of Medical Sciences (KAUMS), Kashan,4 Department of Nutrition School of Allied Medical Sciences, Ahvaz Jundishapur University of Medical Sciences, Ahvaz5 Faculty of Physical Education and Sport Sciences, Tehran University, Tehran,2 Department of Nutrition, Science and Research Branch, Islamic Azad University, Tehran 6 Nutritional Health Team (NHT), Universal Scientific Education and Research Network (USERN), Tehran2 Department of Nutrition, Science and Research Branch, Islamic Azad University, Tehran3 Research Center for Biochemistry and Nutrition in Metabolic Diseases, Institute for Basic Sciences, Kashan University of Medical Sciences (KAUMS), Kashan20250106Background: Earlier studies about the influence of vitamin D (Vit D) supplementation on patients with inflammatory bowel disease (IBD) reported inconsistent results. Current comprehensive systematic review and meta‑analysis was conducted to assess the effect of Vit D supplementation on clinical and subclinical factors in patients with IBD. Methods: PubMed, Scopus, and Web of Science databases were searched for relevant randomized controlled trials (RCTs) on the effect of Vit D supplementation in IBD patients, published up to March 2023. Data were analyzed by the random‑effect model. Heterogeneity was assessed by Cochran’s Q test and I‑square (I2 ) statistic. The mean differences (MDs) were calculated as the summary effect size. Results: We included nine related articles, and our findings indicated that vitamin D administration increased serum vitamin D levels compared to placebo (weighted mean difference (WMD): 12.08; 95% confidence interval (95% CI): 9.06, 15.09; I2 = 97.01%; P < 0.001) in IBD patients. However, it had no significant influence on disease activity (standardized mean difference (SMD): 0.27; 95% CI: ‑0.42, 0.95; I2 = 91.7%; P < 0.001) or serum levels of C‑reactive protein (CRP) (WMD: ‑1.42; 95% CI: ‑3.90, 1.06; I2 = 41.9%; P = 0.262). Conclusions: Current meta‑analysis showed a significant effect of Vit D supplementation on increasing serum cholecalciferol. However, no significant effects of Vit D supplementation on the disease activity and serum levels of CRP were seen. Further studies are needed to expand current knowledge in this issue and found a significant increment in serum 25‑hydroxy cholecalciferol concentrations following Vit D supplementation in IBD patients.http://ijpm.mui.ac.ir/index.php/ijpm/article/view/2956http://ijpm.mui.ac.ir/index.php/ijpm/article/download/2956/717718796