Effect of probiotics or prebiotics on thyroid function: A meta-analysis of eight randomized controlled trials.

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• 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.

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.

• 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.

• 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.