Plain language summary
The gut microbiome is thought to play a role in thyroid disorders, mediated by regulating iodine uptake, degradation and enterohepatic cycling of thyroid hormones, and differences in microbiome composition between patients with thyroid disorders and healthy individuals have been observed. The aim of this systematic review and meta-analysis was to evaluate the effect of pro-, pre- and synbiotics on thyroid function (thyroid stimulating hormone (TSH), free thyroxine (fT4) and free triiodothyronine (fT3) and thyroid stimulating hormone receptor antibody (TRAb)) in patients with and without thyroid disorders. 8 randomised controlled trials including 367 participants were included in the review and meta-analysis. Neither pro-, pre- nor synbiotics had a significant effect on TSH, fT4 or fT3 but pre- and probiotics lead to a significant reduction in TRAb in patients with Graves’ disease.
Expert Review
Conflicts of interest:
None
Take Home Message:
- Current evidence does not support a measurable effect of probiotic, prebiotic or symbiotic supplementation on thyroid hormone levels.
- There may be some benefits of these supplements for patients with Grave’s disease, in terms of lowering their thyroid stimulating hormone antibody levels.
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
Research has highlighted the important role that the gut microbiome might play in thyroid function. As such, the potential role for probiotics and prebiotics to manipulate thyroid function has been considered. Given the inconsistencies in study findings, this systematic review aimed to assess the current consensus in the research.
Methods
- This systematic review was completed in accordance with the PRISMA guidelines.
- The search was performed using the following databases: MEDLINE, Scopus, Web of Science and Embase, plus a manual search and search of grey literature.
- After exclusions, eight peer-reviewed randomised controlled trials were included in the systematic review and meta analysis.
- Studies were conducted in China, Iran and Italy and included a range of different probiotic, prebiotic and synbiotic supplements at varying doses.
- The study included a heterogeneous sample of 367 participants, comprising individuals at risk of thyroid disorders, those diagnosed with thyroid disorders, individuals with obesity, and postmenopausal women.
- A number of outcome measures were considered including: free triiodothyronine (fT3), free thyroxine (fT4), thyroid stimulating hormone (TSH), and thyroid stimulating hormone receptor antibody (TRAb) levels.
- Three studies were found to have low risk of bias, with four studies raising concerns of bias and one being deemed to have a high risk of bias.
Results
- The meta-analysis showed no significant differences (following supplementation) in a number of key hormones: thyroid stimulating hormone (TSH) (SMD: -0.01, 95% CI: −0.21, 0.20); free thyroxine (fT4) (SMD: 0.04, 95% CI: −0.29, 0.21); free triiodothyronine (FT3) (SMD: 0.45, 95% CI: −0.14, 1.03).
- Analysis revealed supplementation was associated with a significant reduction in thyroid stimulating hormone receptor antibody (TRAb) levels (SMD: -0.85, 95% CI: -1.54, -0.15).
Conclusion
- The meta-analysis would suggest that supplementing with probiotics, prebiotics and synbiotics has little impact on the level of thyroid hormones.
- Supplementing with probiotics, prebiotics and synbiotics may, however, have an impact on thyroid stimulating hormone receptor antibody levels, by reducing them.
Clinical practice applications:
- Current research evidence does not support the role of probiotics, prebiotics or synbiotics in influencing thyroid hormone levels.
- The use of probiotics, prebiotics and synbiotics may be a helpful additional strategy in managing patients with Grave’s disease, where thyroid stimulating hormone receptor antibody levels are raised.
Considerations for future research:
- Future research would benefit from focusing on individual sample groups with specific thyroid diagnoses.
- Additional studies would benefit from comparing the effects of probiotics, prebiotics and synbiotics in patients with Grave’s Disease.
- Since hormone levels do not always correlate well with subjective experience of thyroid symptoms, future studies might like to consider patient-report measures of health and wellbeing.
Abstract
BACKGROUND Microbiome-directed therapies are increasingly utilized to optimize thyroid function in both healthy individuals and those with thyroid disorders. However, recent doubts have been raised regarding the efficacy of probiotics, prebiotics, and synbiotics in improving thyroid function. This systematic review aimed to investigate the potential relationship between probiotics/prebiotics and thyroid function by analyzing the impact on thyroid hormone levels. METHODS We conducted a comprehensive systematic review and meta-analysis of randomized controlled trials that investigated the effects of probiotics, prebiotics, and synbiotics on free triiodothyronine (fT3), free thyroxine (fT4), thyroid stimulating hormone (TSH), and thyroid stimulating hormone receptor antibody (TRAb) levels. We searched for articles from PubMed, Scopus, Web of Science, and Embase up until April 1st, 2023, without any language restriction. Quantitative data analysis was performed using a random-effects model, with standardized mean difference (SMD) and 95% confidence interval as summary statistics. The methods and results were reported according to the PRISMA2020 statement. RESULTS A total of eight articles were included in this review. The meta-analysis showed no significant alterations in TSH (SMD: -0.01, 95% CI: -0.21, 0.20, P = 0.93; I2: 0.00%), fT4 (SMD: 0.04, 95% CI: -0.29, 0.21, P = 0.73; I2: 0.00%) or fT3 (SMD: 0.45, 95% CI: -0.14, 1.03, P = 0.43; I2: 78.00%), while a significant reduction in TRAb levels was observed (SMD: -0.85, 95% CI: -1.54, -0.15, P = 0.02; I2: 18.00%) following probiotics/prebiotics supplementation. No indication of publication bias was found. CONCLUSIONS Probiotics/prebiotics supplementation does not influence thyroid hormone levels, but may modestly reduce TRAb levels in patients with Graves' disease.
Methodological quality
Jadad score
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Not applicable
Allocation concealment
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Not applicable