Endocrine Abstracts

Background: There is bidirectionality in the relationship between the thyroid and the gut. Based on recent studies, dysfunctional thyroids could predispose to colorectal cancer by affecting gut health. More specifically, it has been identified that hyperthyroidism, characterized by the overproduction of thyroid hormones, can result in microbiome imbalances in the gut, which create an inflammatory state that may promote cancer.

Objective: The issue is that despite growing data supporting that hyperthyroidism alters gut microbiota composition, there is a lack of research demonstrating its role as a risk factor in colorectal cancer. This review thus attempts to answer the question of whether hyperthyroidism-induced gut dysbiosis constitutes a risk factor for colorectal cancer and whether this risk can be mitigated through microbiome-directed therapies.

Methods: We performed a systematic literature search on multiple databases including PubMed and Web of Science, focusing on studies (2000-2024) about the thyroid-gut axis and colorectal cancer (CRC).

Results: This unbiased review revealed that hyperthyroidism-induced dysbiosis may contribute to precancerous conditions by increasing harmful bacterial genera like "pathogenic Clostridium species and Enterococcus" while decreasing beneficial genera such as "Faecalibacterium and Roseburia spp." In addition, an imbalance between Bacillus and Actinobacteria species is observed. Another revelation is that hyperthyroid patients have low diversity of gut microorganisms, leading to poor absorption of iodine, selenium, and zinc, which are important for thyroid function. These changes result in a pro-inflammatory state.

Conclusion: This review highlights that the management of hyperthyroidism and prevention of cancer could be potential targets of therapy if we understand the bidirectional thyroid-gut axis. Future studies should examine these approaches and evaluate the impact on the microbiome and the risk factors associated with the thyroid.