SIMULTANEOUS INTAKE OF LIQUID L-T4 FORMULATION AND IRON SALT: FACT OR FICTION?

Context: Hypothyroidism and iron deficiency are among the most common pathologies in population. Therefore, there are a lot of patients assuming both iron salt supplements and levothyroxine therapy. Objective: To evaluate the effect of iron salt intake on L-T4 absorption among different L-T4 formulations. Materials and methods: A PubMed/MEDLINE, Web of Science, and Scopus research was performed. Original studies and reviews written in English and published online up to 21 December 2022 were selected and reviewed. The final reference list was defined based on the relevance of each paper to the scope of this review. Results: The data show an impaired absorption of L-T4 in tablets formulation when taken concomitantly with iron salt supplements. These phenomena seem to be circumvented by new L-T4 formulations. Conclusion: Liquid L-T4 formulations can be ingested with iron salts, with no impairment of absorption. More studies are necessary to confirm these data for soft-gel capsules L-T4.