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

Gut microbes. 2023;15(1):2221429

Plain language summary

Microbiota are communities of microorganisms that co-exist with the host ecosystem in a specific environment. The term microbiome refers to the microbial genome. The aim of this study was to investigate the effect of supplementing older adults with 60,000 IU of vitamin D per month on the gut microbiome for a period of five years, using a subsample (n = 835) of participants recruited from the large population-based D-Health Trial. This study is based on a subsample from the D-Health Trial, which was a randomised, double-blind trial with two parallel arms. Participants were randomly allocated (1:1 ratio) to monthly doses of either 60,000 IU of cholecalciferol (vitamin D3) or matching placebo. Results showed that monthly doses of 60,000 IU vitamin D over 5 years did not alter the composition of the gut microbiome in a population that is largely vitamin D replete. Authors conclude that further investigation is required to examine whether non-bolus doses of vitamin D would influence the gut microbiome or whether vitamin D supplementation would be beneficial in populations with a higher prevalence of vitamin D deficiency.


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.

Lifestyle medicine

Fundamental Clinical Imbalances : Digestive, absorptive and microbiological
Patient Centred Factors : Mediators/Gut microbiome
Environmental Inputs : Nutrients ; Microorganisms
Personal Lifestyle Factors : Nutrition
Functional Laboratory Testing : Stool
Bioactive Substances : Vitamin D3 ; Cholecalciferol

Methodological quality

Jadad score : 5
Allocation concealment : Yes