• Chris Wallace, Morris Gordon, Vassiliki Sinopoulou, and Berkeley N Limketkai.
• Pennine Acute Hospitals NHS Trust, Manchester, UK.
• Cochrane Db Syst Rev. 2023 Oct 2; 10 (10): CD011806CD011806.

BackgroundVitamin D possesses immunomodulatory properties and has been implicated in the pathogenesis and severity of inflammatory bowel disease (IBD). Animal studies and emerging epidemiological evidence have demonstrated an association between vitamin D deficiency and worse disease activity. However, the role of vitamin D for the treatment of IBD is unclear.ObjectivesTo evaluate the benefits and harms of vitamin D supplementation as a treatment for IBD.Search MethodsWe used standard, extensive Cochrane search methods. The latest search date was Jun 2023.Selection CriteriaWe included randomised controlled trials (RCTs) in people of all ages with active or inactive IBD comparing any dose of vitamin D with another dose of vitamin D, another intervention, placebo, or no intervention. We defined doses as: vitamin D (all doses), any-treatment-dose vitamin D (greater than 400 IU/day), high-treatment-dose vitamin D (greater than 1000 IU/day), low-treatment-dose vitamin D (400 IU/day to 1000 IU/day), and supplemental-dose vitamin D (less than 400 IU/day).Data Collection And AnalysisWe used standard Cochrane methods. Our primary outcomes were 1. clinical response for people with active disease, 2. clinical relapse for people in remission, 3. quality of life, and 4. withdrawals due to adverse events. Our secondary outcomes were 5. disease activity at end of study, 6. normalisation of vitamin D levels at end of study, and 7. total serious adverse events. We used GRADE to assess certainty of evidence for each outcome.Main ResultsWe included 22 RCTs with 1874 participants. Study duration ranged from four to 52 weeks. Ten studies enroled people with Crohn's disease (CD), five enroled people with ulcerative colitis (UC), and seven enroled people with CD and people with UC. Seventeen studies included adults, three included children, and two included both. Four studies enroled people with active disease, six enroled people in remission, and 12 enroled both. We assessed each study for risk of bias across seven individual domains. Five studies were at low risk of bias across all seven domains. Ten studies were at unclear risk of bias in at least one domain but with no areas of high risk of bias. Seven studies were at high risk of bias for blinding of participants and assessors. Vitamin D (all doses) versus placebo or no treatment Thirteen studies compared vitamin D against placebo or no treatment. We could not draw any conclusions on clinical response for UC as the certainty of the evidence was very low (risk ratio (RR) 4.00, 95% confidence interval (CI) 1.51 to 10.57; 1 study, 60 participants). There were no data on CD. There may be fewer clinical relapses for IBD when using vitamin D compared to placebo or no treatment (RR 0.57, 95% CI 0.34 to 0.96; 3 studies, 310 participants). The certainty of the evidence was low. We could not draw any conclusions on quality of life for IBD (standardised mean difference (SMD) -0.13, 95% CI -3.10 to 2.83 (the SMD value indicates a negligent decrease in quality of life, and the corresponding CIs indicate that the effect can range from a large decrease to a large increase in quality of life); 2 studies, 243 participants) or withdrawals due to adverse events for IBD (RR 1.97, 95% CI 0.18 to 21.27; 12 studies, 1251 participants; note 11 studies reported withdrawals but recorded 0 events in both groups. Thus, the RR and CIs were calculated from 1 study rather than 12). The certainty of the evidence was very low. High-treatment-dose vitamin D versus low-treatment-dose vitamin D Five studies compared high treatment vitamin D doses against low treatment vitamin D doses. There were no data on clinical response. There may be no difference in clinical relapse for CD (RR 0.48, 95% CI 0.23 to 1.01; 1 study, 34 participants). The certainty of the evidence was low. We could not draw any conclusions on withdrawals due to adverse events for IBD as the certainty of the evidence was very low (RR 0.89, 95% CI 0.06 to 13.08; 3 studies, 104 participants; note 2 studies reported withdrawals but recorded 0 events in both groups. Thus, the RR and CIs were calculated from 1 study rather than 3). The data on quality of life and disease activity could not be meta-analysed, were of very low certainty, and no conclusions could be drawn. Any-treatment-dose vitamin D versus supplemental-dose vitamin D Four studies compared treatment doses of vitamin D against supplemental doses. There were no data on clinical response and relapse. There were no data on quality of life that could be meta-analysed. We could not draw any conclusions on withdrawals due to adverse events for IBD as the certainty of the evidence was very low (RR 3.09, 95% CI 0.13 to 73.17; 4 studies, 233 participants; note 3 studies reported withdrawals but recorded 0 events in both groups. Thus, the RR and CIs were calculated from 1 study rather than 4).Authors' ConclusionsThere may be fewer clinical relapses when comparing vitamin D with placebo, but we cannot draw any conclusions on differences in clinical response, quality of life, or withdrawals, due to very low-certainty evidence. When comparing high and low doses of vitamin D, there were no data for clinical response, but there may be no difference in relapse for CD. We cannot draw conclusions on the other outcomes due to very low certainty evidence. Finally, comparing vitamin D (all doses) to supplemental-dose vitamin D, there were no data on clinical relapse or response, and we could not draw conclusions on other outcomes due to very low certainty evidence or missing data. It is difficult to make any clear recommendations for future research on the basis of the findings of this review. Future studies must be clear on the baseline populations, the purpose of vitamin D treatment, and, therefore, study an appropriate dosing strategy. Stakeholders in the field may wish to reach consensus on such issues prior to new studies.Copyright © 2023 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.

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