What Endocrinologists Should Know About Iodine: Population Deficiency, Individual Excess and Misinformation in the United Kingdom.

Iodine deficiency, once considered eliminated in the United Kingdom, has re-emerged, particularly among women of reproductive age, in whom requirements are increased during pregnancy and lactation. The declining consumption of dairy and white fish, the emerging use of unfortified plant-based milk alternatives, and the absence of a national iodisation policy have contributed to a return of mild to moderate iodine deficiency. Vegans and individuals avoiding dairy are at particular risk. Simultaneously, social-media-driven wellness trends promote 'thyroid detoxes' or 'iodine resets' and kelp-based supplements that deliver supraphysiological iodine doses far exceeding recommended intake. Endocrinologists now face a dual challenge: widespread under-recognition of population iodine insufficiency and a growing minority of patients presenting with iodine-induced thyroid dysfunction. This review summarises current UK iodine status, the physiological and clinical relevance of iodine to thyroid and neurodevelopmental health, modern dietary risk factors and the clinical approach to those influenced by online misinformation. Routine dietary counselling and public health fortification represent cost-effective interventions to prevent both extremes. Population-based solutions would correct iodine status efficiently and align the UK with other high-income countries.