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.
Expert Review
Conflicts of interest:
None
Take Home Message:
- Overall, current evidence regarding the effect of vitamin D supplementation on the diversity of the gut microbiome is inconclusive. There is limited evidence to support the benefit of vitamin D, particularly in light of the findings of the D-Health Trial.
Evidence Category:
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X
A: Meta-analyses, position-stands, randomized-controlled trials (RCTs)
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B: Systematic reviews including RCTs of limited number
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C: Non-randomized trials, observational studies, narrative reviews
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D: Case-reports, evidence-based clinical findings
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E: Opinion piece, other
Summary Review:
Introduction
This study aimed to analyse data using a subsample (n=835) of participants from the D-Health Trial, a randomised, double-blind, placebo-controlled trial, to investigate the effect of 60,000 IU of vitamin D supplementation per month for five years on the gut microbiome of older Australians.
Methods
- 835 Australians with a mean age of 69.4 years were randomised to an intervention group - 60,000 IU of vitamin D3 monthly for 5 years (n=418) or placebo group (n=417).
- Stool samples were collected and the gut microbiome was characterised using 16S rRNA gene sequencing. Linear regression analysis compared alpha diversity indices, and the ratio of Firmicutes to Bacteroidetes between the two groups. Between-sample (beta) diversity was analysed and PERMANOVA was used to test for significant clustering according to randomisation group. The difference in the abundance of 20 genera was also analysed between the two groups using a negative binomial regression model with adjustment for multiple testing.
- Participants were largely vitamin D replete. The mean 25(OH)D concentration in the placebo group was a little higher than that reported in the 2011/2012 Australian Health survey (77 versus 69 nmol/L), but this may be due to differences in the geographic distribution of participants or the timing of blood sampling.
Results
- Monthly supplementation of 60,000 IU of Vitamin D for 5 years did not alter measures of alpha diversity or the Firmicutes-to-Bacteroidetes ratio.
- Vitamin D supplementation had no effect on the beta diversity of the gut microbiome as measured by Bray-Curtis and UniFrac distances (p values 0.10 and 0.61, respectively).
- At baseline, Firmicutes and Bacteroidetes phyla represented more than 80% of the total sequencing reads. Vitamin D did not alter measures of alpha diversity or the Firmicutes-to-Bacteroidetes ratio after 5 years.
Conclusion
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.
Limitations
- Dietary patterns/gut microbiome profiles at baseline were not measured so could not adjust for these factors.
- Gut metabolites were not measured, so were unable to assess the effect of vitamin D on these.
- Predicted instead of measured baseline 25(OH)D concentrations were used therefore misclassification of participants’ baseline vitamin D status may have occurred.
Clinical practice applications:
- Whilst the results are likely to be reasonably generalisable to populations with a low prevalence of vitamin D deficiency, these findings cannot be used to infer the effect on the microbiome of treating vitamin D deficiency. Assessing vitamin D status in clinical practice prior to supplementation is therefore indicated.
Considerations for future research:
- Further investigation is needed to examine whether non-bolus doses of vitamin D would have an effect on the gut microbiome and whether vitamin D supplementation would be beneficial in populations with a higher prevalence of vitamin D deficiency.
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.
Methodological quality
Jadad score
:
5
Allocation concealment
:
Yes
