The interrelationship between iron load and thyroid function is pretty well accepted, but I post here a paper showing the effect in children (can extrapolate safely to adults I think). It underlines the need for good iron loading to help rule out or confirm hypothyroidism.
Journal of Clinical and Diagnostic Research. 2018 Jan, Vol-12(1): BC01-BC05
Thyroid Function among Children with Iron Deﬁciency Anaemia: Pre and Post Iron Replacement Therapy
Metabolism of thyroid hormones and iron is quite interdependent. Data indicates that Iron Deﬁciency (ID) could impair thyroid metabolism.
To investigate the possible occurrence of thyroid dysfunction among children with isolated Iron Deﬁciency Anaemia (IDA) of various severities, and test if the oral iron replacement therapy alone can reverse the associated thyroid function disturbances, if present or additional therapies are required.
Materials and Methods:
This prospective study was carried out on 60 children selected from the attendants to the outpatient paediatric clinics of Al-Azhar University, Assiut and Qena university hospitals, Egypt, in addition to 60 controls. Complete blood count, thyroid proﬁle, ferritin, iron, Total Iron Binding Capacity (TIBC), Transferrin Saturation% (TFS%), unsaturated iron binding capacity and Urinary Iodine Excretion (UIE) were assessed in the studied groups at baseline, then haemoglobin level and thyroid proﬁle repeated among the studied patients after three months of oral iron supplementation therapy. Thyroid proﬁle and ferritin were measured using commercially available Enzyme Linked Immunosorbent Assay (ELISA) kits; while, iron, TIBC and UIE were measured using colorimetric methods.
Signiﬁcant higher serum Thyroid Stimulating Hormone (TSH) levels with signiﬁcant lower serum levels of Free Triiodothyronine (FT3) and Free Thyroxine (FT4) among patients versus controls (p<0.001 for all). Signiﬁcant positive correlation between serum iron and FT3 (r=0.284, p<0.05) with signiﬁcant negative correlations between TSH versus both serum iron (r=-0.635, p<0.001) and ferritin (r=-0.342, p<0.01). Signiﬁcant decrease in the serum levels of TSH, with signiﬁcant increase in the serum levels of FT3 and FT4 (p<0.001 for all) to euthyroid status following oral iron replacement therapy.
Subclinical or primary hypothyroidism can occur among children suffering from moderate to severe IDA, which is reversible following oral iron replacement therapy only, without need to add thyroid replacement therapy.