In a systematic review and meta-analysis by Guzman et al., which included five studies and a total of 253 IBD patients, vitamin D supplementation was associated with a mean reduction of 1.52 points in the Harvey Bradshaw Index (HBI) (95% CI 0.14–2.90; p = 0.03; I2 = 51%) and a decrease in CRP levels (mean difference 3.70 mg/L; 95% CI 0.10–7.29; p = 0.04; I2 = 0%) [53]. Here, CRP is linked to inflammatory bowel disease.