Thyroid and Nutrition: Interplay, Clinical Implications, and Public Health Perspectives

A bstract The thyroid gland and nutritional status are bound in a profound, bidirectional relationship that spans from subcellular biochemistry to national public health policy. Adequate availability of key micronutrients—iodine, selenium, zinc, iron, vitamin D, and vitamin A—is indispensable for every phase of thyroid hormone biosynthesis, peripheral activation, and genomic signaling. Conversely, thyroid dysfunction itself disrupts macronutrient metabolism, energy homeostasis, and micronutrient absorption, creating a self-reinforcing cycle of metabolic deterioration. Dietary constituents, including goitrogens, processed foods, ultra-processed carbohydrates, and specific drug–nutrient interactions, further modulate thyroid function in both clinically apparent and subclinical ways. At the population level, iodine deficiency disorders remain the leading preventable cause of intellectual disability globally, while emerging data point to excessive iodine intake as an underappreciated driver of autoimmune thyroid disease. This review comprehensively examines the molecular and clinical evidence linking nutrition to thyroid health, the public health burden of micronutrient-related thyroid disorders, dietary and lifestyle strategies for optimizing thyroid function, and priority areas for future research, with particular attention to the contexts of South Asia and Bangladesh.