The effects of synbiotic supplementation on thyroid function and inflammation in hypothyroid patients: A randomized, double-blind, placebo-controlled trial

Background: There is a positive link between thyroid homeostasis and the composition of gut microbiota. A limited number of studies have suggested the efficacy of probiotic products on levothyroxine metabolism and thyroid hormone activity. Therefore, the purpose of this study was to investigate the effect of synbiotic supplementation on thyroid function, inflammation markers, and blood pressure in subjects with hypothyroidism. Methods: This study was conducted as a randomized, double-blind, placebo-controlled trial involving 60 patients with hypothyroidism. Participants were randomly recruited into two groups to receive either 500 mg/day of synbiotic (n = 30) or a placebo (n = 30) for 8 weeks. Results: Thyroid-stimulating hormone concentration, levothyroxine dose, and fatigue severity scale score were significantly decreased after the 8-week intervention in the synbiotic group (P < 0.05), while there were no significant differences seen in the placebo group. In addition, FT3 at the end of intervention was significantly higher (P = 0.001) in both groups, although these changes were not significant between the two groups (P = 0.259). Synbiotic supplements led to a significant elevation in serum CRP (P = 0.006), but this increase was not significant between groups (P = 0.699). Moreover, no statistical significance was observed within or between groups in terms of anti-thyroid peroxidase, systolic blood pressure and diastolic blood pressure (P > 0.05). Conclusion: Synbiotic supplementation among hypothyroid patients for 8 weeks may have beneficial effects on thyroid function. Further studies with larger sample size and longer duration are needed to confirm the current findings.