The effect of vitamin D supplementation on the gut microbiome in older Australians – Results from analyses of the D-Health Trial

ABSTRACT

Observational studies suggest a link between vitamin D and the composition of the gut microbiome, but there is little evidence from randomized controlled trials of vitamin D supplementation. We analyzed data from the D-Health Trial, a randomized, double-blind, placebo-controlled trial. We recruited 21,315 Australians aged 60–84 y and randomized them to 60,000 IU of vitamin D₃ or placebo monthly for 5 y. Stool samples were collected from a sample of 835 participants (417 in the placebo and 418 in the vitamin D group) approximately 5 y after randomization. We characterized the gut microbiome using 16S rRNA gene sequencing. We used linear regression to compare alpha diversity indices (i.e. Shannon index (primary outcome), richness, inverse Simpson index), and the ratio of Firmicutes to Bacteroidetes between the two groups. We analyzed between-sample (beta) diversity (i.e. Bray Curtis distance and UniFrac index) using principal coordinate analysis and used PERMANOVA to test for significant clustering according to randomization group. We also assessed the difference in the abundance of the 20 most abundant genera between the two groups using negative binomial regression model with adjustment for multiple testing. Approximately half the participants included in this analysis were women (mean age 69.4 y). Vitamin D supplementation did not alter the Shannon diversity index (mean 3.51 versus 3.52 in the placebo and vitamin D groups, respectively, p = 0.50). Similarly, there was little difference between the groups for other alpha diversity indices, the abundance of different genera, and the Firmicutes-to-Bacteroidetes ratio. We did not observe clustering of bacterial communities according to randomization group. In conlusion, monthly doses of 60,000 IU of vitamin D supplementation for 5 y did not alter the composition of the gut microbiome in older Australians.

KEYWORDS:

• Gut microbiome
• vitamin D supplementation
• randomized controlled trial

Acknowledgments

We would like to acknowledge the D-Health Trial staff and members of the Data and Safety Monitoring Board (Patricia Valery, Ie-Wen Sim, and Kerrie Sanders), and Services Australia for supplying Pharmaceutical Benefits Scheme (PBS) and Medicare Benefits Schedule (MBS) data. We also extend our thanks to the D-Health Trial participants who committed to this research.

Disclosure statement

No potential conflict of interest was reported by the authors.

Authors’ contributions

DW, PW, GH, DE, MK, RO, JV, AV, CB, BDR, PE, DM, BA, and RN designed the trial. CB, BDR, MW, DM, FH, and RN were involved in recruitment, data collection, and curation. HP, MW, FH, and RN carried out the investigations and formal analysis. HP wrote the first draft of the report with input from MW, FH, and RN. All authors approved the pre-specified analysis plan and were involved in reviewing and editing the final draft. MW, FH, and RN provided supervision.

Availability of data and materials

The data that support the findings of this study are not openly available. The data are available upon reasonable request and subject to approval.

List of abbreviations

BMI = body mass index

CI = confidence interval

IU = international units

OTU = operational taxonomic units

RCT = randomized controlled trial

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/19490976.2023.2221429

Additional information

Funding

This work is supported by the National Health and Medical Research Council (NHMRC) project grants [Grant numbers GNT1046681, GNT1120682]. PR Ebeling, RE Neale, PM Webb, and DC Whiteman are/were supported by fellowships from the NHMRC [Grant numbers GNT1197958, GNT1060183, GNT1173346, GNT1155413]. DSA McLeod is supported by a Metro North Clinician Research Fellowship and a Queensland Advancing Clinical Research Fellowship. H Pham is supported by a University of Queensland PhD Scholarship. The vitamin D assays were performed at the University of Western Australia, supported by infrastructure funding from the Western Australian State Government in partnership with the Australian Federal Government, through Bioplatforms Australia and the National Collaborative Research Infrastructure Strategy (NCRIS).