Limitations
depression, hypothyroidism
HYPOTHYROIDISM
One limitation is the generalizability of the results. Although Baqiyatallah is a referral hospital and the sample was socially, culturally and geographically diverse, we had plenty of inclusion and exclusion criteria. Several protocol amendments had to be made, because of the low response rate to the advertisement and fliers, and difficulty in reaching the final sample size. Another limitation was adjustment for 4 confounders in the ANCOVA analysis. Since the sample size was small (less than 30 patients in each group), adjusting 4 confounders widened the 95% confidence interval (CI) values, and lead to a less accurate result. We also failed to perform subgroup analyses (i.e. based on type of hypothyroidism or age groups) to find out the reason for non-significant results regarding thyroid hormones and depression, because of the small sample size. Measurement of the richness and diversity of gut microbiota was outside the scope of this study; hence, it is inconclusive through which mechanisms synbiotic supplementation has induced the observed changes. Budget limitation also prevented us from assessing more important outcomes including serum T3 level.