Study Title
Effect of Vitamin D Supplementation on Human Gut Microbiota: A Systematic Review of Randomized Controlled Trials
Principal Investigator
Falak Zeb, Tareq Osaili, Mona Hashim, Nadia Alkalbani, Dimitrios Papandreou, Leila Cheikh Ismail, Farah Naja, Hadia Radwan, Hayder Hasan, Reyad Shakir Obaid, Ioannis Savvaidis, Sharifa AlBlooshi, Iftikhar Alam
Affiliation
Research Institute of Medical and Health Sciences, University of Sharjah, Sharjah, United Arab Emirates; Department of Clinical Nutrition and Dietetics, College of Health Sciences, University of Sharjah, UAE; additional affiliations including Jordan University of Science and Technology, University of Oxford, and American University of Beirut.
Start Date
January 2015 (literature search coverage)
End Date
November 2024 (literature search coverage)
Study Objective
To examine the effects of vitamin D supplementation on human gut microbiota composition and diversity by analysing findings from randomized controlled trials (RCTs).
Short Abstract
Background: Vitamin D has been suggested to play an important role in maintaining overall health, including potential effects on gut microbiota composition, which influences physiological and immune-related processes.
Objective: To examine the effects of vitamin D supplementation on gut microbiota composition and diversity in humans.
Methods: A systematic review following PRISMA guidance searched MEDLINE, Web of Science, Scopus, and the Cochrane Library for studies published between January 1, 2015 and November 30, 2024. Randomized controlled trials investigating vitamin D supplementation and gut microbiota outcomes measured through high-throughput sequencing techniques were included. A total of 14 RCTs involving 1,458 participants with varying health conditions and supplementation regimens were analysed.
Results: Vitamin D supplementation appeared to modulate gut microbiota composition, with increases in taxa associated with gut and immune health, including Bifidobacterium and Lactobacillus, and an increased Bacteroidetes-to-Firmicutes ratio. Some studies reported improvements in α- and β-diversity, although findings varied according to dosage, duration, and baseline vitamin D status. Changes in biomarkers such as calprotectin and trimethylamine N-oxide were also reported.
Conclusion: Findings are promising but heterogeneous. Methodological variation limits causal interpretation and highlights the need for standardized approaches and long-term RCTs to determine clinical relevance and implications for personalised nutrition strategies.
Study Design
Systematic review of randomized controlled trials (RCTs).
Population
Participants enrolled in randomized controlled trials investigating vitamin D supplementation and gut microbiota composition, including individuals with varying health status.
Sample Size
1,458 participants across 14 randomized controlled trials.
Inclusion Criteria
Randomized controlled trials assessing the impact of vitamin D supplementation on human gut microbiota using high-throughput sequencing methods.
Exclusion Criteria
Non-randomized studies, studies not evaluating vitamin D supplementation, studies without microbiota outcomes measured through sequencing methods, and non-human studies. (Inferred from stated inclusion criteria.)
Intervention/Exposure
Vitamin D supplementation with varying doses, durations, and participant baseline vitamin D status.
Outcome Measures
Gut microbiota composition and diversity (α- and β-diversity), abundance of bacterial taxa, Bacteroidetes/Firmicutes ratio, microbial biomarkers including calprotectin and trimethylamine N-oxide (TMAO).
Funding Source
Not specified in abstract/source reviewed.
Collaborating Institutions
University of Sharjah, Jordan University of Science and Technology, University of Oxford, American University of Beirut, and collaborating institutional partners.
Ethics Approval
Not applicable (systematic review).
Publication Status
Published in July 2025 in Nutrition Reviews (DOI: 10.1093/nutrit/nuaf120).
Keywords
Vitamin D supplementation, gut microbiota, microbiome, randomized controlled trials, microbial diversity, immune regulation, systematic review.
Data Collection Methods
Systematic database search (MEDLINE, Web of Science, Scopus, Cochrane Library) and synthesis of RCT evidence following PRISMA methodology; microbiota outcomes assessed using sequencing technologies.
Primary Data Availability
Not applicable (systematic review of published studies).
Contact Information
Falak Zeb