Are probiotics, prebiotics, and synbiotics beneficial in primary thyroid diseases? A systematic review with meta-analysis.

A number of studies indicate the presence of a thyroid-gut axis and the important influence of the gut microbiota on thyroid function. As prebiotics, probiotics and synbiotics show therapeutic potential in the treatment of intestinal dysbiosis, the aim of this review is to evaluate the efficacy of their supplementation in primary thyroid diseases. Electronic databases (Ovid MEDLINE, Embase, CENTRAL), registers of clinical trials, and grey literature up to 6 October 2022 were searched for randomised controlled trials (RCTs) meeting pre-specified inclusion criteria. The protocol was registered in PROSPERO (CRD42021235054). After screening 1,721 references, two RCTs were identified, which included 136 hypothyroid participants in total. Meta-analysis of the results after eight weeks of supplementation with predominantly Lactobacillus and Bifidobacterium strains indicated a clinically and statistically nonsignificant decrease in TSH (MD -0.19 mIU/L; 95% CI -0.43 to 0.06; I Low-certainty evidence from two randomised trials, suggests that routine administration of probiotics, prebiotics or synbiotics may result in little to no benefit in patients with primary hypothyroidism.