Vitamin D status in relation to Crohn's disease: Meta-analysis of observational studies

• Growing evidence suggests a relationship between vitamin D status and the progression of Crohn's disease.
• Vitamin D status in Crohn's disease compared with healthy controls has inconsistent results in deficiency and correlations with disease activity.
• Summarizing earlier evidence on the association of vitamin D status and Crohn's disease, this meta-analysis revealed that CD patients had lower mean levels of 25(OH)D compared with healthy controls.
• A significant correlation was seen between latitude and 25(OH)D levels. More than half of the patients with CD had vitamin D deficiency.
• Individuals with lower concentrations of 25(OH)D had greater disease activity than those with sufficient concentrations.

ObjectivesInconsistent findings have been published regarding vitamin D status among patients with Crohn's disease (CD) and the association with disease severity. We aimed to perform a meta-analysis evaluating serum 25-hydroxy vitamin D and 1,25 dehydroxyvitamin D among CD patients compared with healthy and non-healthy controls, the prevalence of vitamin D deficiency, and the association with disease.MethodsWe searched MEDLINE, SCOPUS, EMBASE, and Google Scholar up to March 2015 for observational studies assessing serum vitamin D levels in CD patients. A total of 63 studies were included in the following four meta-analyses: 1) a meta-analysis on the mean difference of 25(OH)D levels in CD patients compared with healthy (number of studies = 27) and non-healthy (n = 25) controls; 2) a meta-analysis on the mean difference of 1,25(OH)2 D3 levels in CD patients compared with healthy (n = 7) and non-healthy (n = 8) controls; 3) a meta-analysis on the prevalence of vitamin D deficiency (n = 34); 4) a meta-analysis on the correlation coefficients between vitamin D status severity of CD (n = 6). Subgroup analysis and meta-regression were used to discover possible sources of between-study heterogeneity.ResultsIt was found that CD patients had lower levels of 25(OH)D compared with healthy (−3.99 ng/mL; 95% confidence interval [CI]: −5.91 to −2.08) but not non-healthy controls (−1.07 ng/mL; 95% CI: −2.84 to 0.70). There was also no significant mean difference for 1,25(OH)2 D3 for both healthy and non-healthy controls. Meta-analysis on the prevalence of vitamin D deficiency showed an overall prevalence of 57.7% (95% CI: 0.502–0.649). An inverse association was observed between serum vitamin D and severity of CD (−0.36; 95% CI: −0.48 to −0.24). Meta-regression showed that mean levels of 25(OH)D were decreased 0.09 for each unit change of latitude among CD patients compared with healthy controls (B = −0.09, P = 0.004, I2 residual = 86.08%).ConclusionsWe found that patients with Crohn's disease had lower serum 25(OH)D concentrations compared with their healthy counterparts, and more than half of them have hypovitaminosis D. Moreover, there was an inverse correlation between circulating 25(OH)D concentrations and severity of Crohn's disease.