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

Systematic review and meta-analysis of 8 randomized controlled trials enrolling 367 participants from China, Iran, and Italy. Adults had thyroid-related conditions or risk states, including Graves’ disease, hypothyroidism, subclinical hypothyroidism, post-thyroidectomy differentiated thyroid cancer, obesity, and postmenopausal status.

Eight randomized controlled trials evaluated oral probiotic, prebiotic, or synbiotic regimens in adults with thyroid disease or risk of thyroid dysfunction. The active products included multistrain probiotic formulations, Bifidobacterium longum, black bean, Elaeagnus angustifolia, and synbiotic capsules containing Lactobacillus, Bifidobacterium, Streptococcus thermophilus, and fructooligosaccharides; reported treatment durations ranged from 4 weeks to 6 months.

Overall, probiotics or prebiotics did not significantly change thyroid hormone measures in the pooled analysis. There was no significant effect on TSH (SMD -0.01, 95% CI -0.21 to 0.20, P=0.93), fT4 (SMD 0.04, 95% CI -0.29 to 0.21, P=0.73), or fT3 (SMD 0.45, 95% CI -0.14 to 1.03, P=0.43). In Graves’ disease, however, supplementation significantly reduced TRAb levels (SMD -0.85, 95% CI -1.54 to -0.15, P = 0.02; I2: 18%). The authors concluded that thyroid hormone effects were not significant overall, but TRAb reduction may indicate a potential benefit in Graves’ disease.

Evidence was limited to 8 trials with 367 participants and substantial variability in populations, interventions, and durations. Most findings were null and the significant TRAb result was subgroup-specific, so generalizability is limited. The review also indicates the need for further well-designed trials with more consistent outcome reporting.