Navigating Iodine Deficiencies and Excesses in Thyroid Health, With Shashank Joshi, MD

Due to significant thyroid disease risk from both under- and overconsumption, iodine intake must be carefully monitored – particularly given the small doses hidden in many popular supplements.1

Presented at the American Association of Clinical Endocrinology (AACE) Annual Meeting 2026 in Las Vegas, Nevada, by Shashank Joshi, MD, a consultant endocrinologist at Lilavati Hospital and Joshi Clinic in Mumbai, this talk details the risks of both excess iodine and iodine deficiency. Joshi highlights the various diseases born from iodine’s interaction with the thyroid, triggered both by too little and too much iodine in the system.1

“Iodine biology becomes immunology. So, what happens when you have too much iodine or too little iodine?” Joshi told HCPLive in an exclusive interview. “The iodine behaves like an immunogen, and the body identifies it as an immunogen, and it attacks it through antibody production. If there is downregulation, then you get hypothyroidism or Hashimoto’s thyroiditis. If it’s upregulated, you will have Graves’ disease.”

Iodine deficiency is a well-studied contributor to goiter and hypothyroidism, as it plays a direct role in the production of thyroid hormone. Mild-to-moderate iodine deficiency can potentially be compensated by increased thyroid activity; however, chronic stimulation of the thyroid eventually increases the prevalence of toxic nodular goiter and hyperthyroidism. Additionally, iodine deficiency can directly impair cognitive function, as thyroid hormones are required for neuronal migration, glial differentiation, and myelination of the central nervous system.2

However, the other side of the coin is similarly damaging. Iodine excess, the less-studied extreme of iodine intake, can lead to Graves’ disease and Hashimoto’s thyroiditis, both of which are driven by immune cell polarization and alterations in gut microbiota. The risk of cardiovascular diseases like hypertension and atherosclerosis is also increased due to endothelial dysfunction, inflammation, and oxidative stress. Further down the line, the development of thyroid cancer can also be influenced by excess iodine, as can learning and memory through neurotoxic effects.3

To address these potential outcomes, Joshi highlights a narrow iodine window, pointing out the thyroid’s intolerance of extremes in either direction. He notes a bell curve in the biology of iodine, with early symptoms of both insufficient and excessive iodine intake appearing similar. The optimal range of iodine for thyroid health, therefore, occupies a relatively narrow space.1

Additionally, Joshi points out the risk of iodine excess posed by everyday intake. Micronutrient supplements, despite being widely used and sold over the counter, are not directly approved by the US Food and Drug Administration (FDA). Because of this, they lack warnings for excess iodine content and can thus stealthily raise levels in a patient’s body. Additionally, iodized salt has become popular over the last few years, leading to another prominent source of iodine without any kind of warning on the risks of excess.1,3

“Whenever a patient is taking any supplement over the counter, they need to read the label and see how much iodine is contained in it,” Joshi said. “You’re taking iodine sometimes through your salt, through your food, and an extra supplement could be creating that perfect storm which you want to avoid. Remember that excess thyroid production or cancer can be a byproduct of excess iodine intake.”

Editors’ Note: Joshi reports disclosures with Abbott, Lilly, Novo Nordisk, Sanofi, Torrent, Celagenex, and others.

References

1. Joshi S. Impact of Iodine on Thyroid Autoimmunity, Goiter and Oncogenesis (Hossein Gharib, MD, Lectureship). Presented at the American Association of Clinical Endocrinology Annual Meeting 2026, Las Vegas, NV. April 22-24, 2026.

2. Zimmermann MB, Boelaert K. Iodine deficiency and thyroid disorders. Lancet Diabetes Endocrinol. 2015;3(4):286-295. doi:10.1016/S2213-8587(14)70225-6

3. Khudair A, Khudair A, Niinuma SA, Habib H, Butler AE. Beyond thyroid dysfunction: the systemic impact of iodine excess. Front Endocrinol (Lausanne). 2025;16:1568807. Published 2025 Apr 2. doi:10.3389/fendo.2025.1568807