Background and Aim Thyroid diseases are among the most common endocrine disorders. Animal and human experiences indicate that iron deficiency disrupts thyroid metabolism. On the other hand, iron therapy can improve thyroid function and even decrease the dose of levothyroxine.
Methods and Materials In this randomized clinical trial, we selected 94 women with hypothyroidism by simple random sampling method and divided them into two equal groups by simple block sampling. At the beginning of the study, we measured and recorded T4, TSH, T3, and iron profiles (Serum iron, total iron-binding capacity, ferritin, Hemoglobin) in all patients. Then, the patients in the intervention group were treated with levothyroxine plus 100 mg oral iron daily for 8 weeks, and the patients in the control group were treated with levothyroxine only. After two months, we measured their T4, TSH, T3 levels and iron profiles in both groups again.
Ethical Considerations The Research Ethics Committee of Arak University of Medical Sciences approved this study (Research Ethics Code: 1396154). Also, the study has been registered at the Iranian Registry of Clinical Trials (Code: IRCT 20151114025031).
Results After 2 months, the TSH Mean±SD serum levels were found as 2.2±1.0 mIU/L and 2.9±1.1 mIU/L for the intervention and control group, respectively (P=0.04). Also, the serum Mean±SD level of T4 and T3 were found as 9.3±1.48 mcg/dL vs. 8.2±0.9 mcg/dL (P=0.01), and 1.6±0.3 ng/mL vs. 1.1±0.3 ng/mL (P=0.01), for two different groups, respectively. 
Conclusion Concurrent administration of iron supplementation with the usual dose of levothyroxine in patients with hypothyroidism decreases THS level and improves laboratory parameters and response to treatment.