Thyroid Health and Selenium: The Critical Role of Adequate Intake from Fetal Development to Adolescence

The thyroid gland plays a crucial role in regulating metabolism and supporting development through the production of the hormones T4 and T3. These hormones are essential during childhood for nervous system myelination, physical growth, puberty, skeletal and dental maturation, and overall metabolic balance. In early infancy, when the hypothalamic–pituitary–thyroid axis is still immature, thyroid dysfunction can result in a range of long-term complications. The metabolism and action of thyroid hormones depend not only on iodine but also on other vital micronutrients, particularly selenium (Se). This narrative review aims to comprehensively examine the role of selenium in maintaining thyroid health from fetal life through adolescence. Selenium is a key micronutrient involved in thyroid development, hormone synthesis, antioxidant defense, and immune regulation, especially during pregnancy and childhood. Inadequate selenium levels may contribute to the onset, progression, and clinical management of various thyroid disorders, particularly hypothyroidism and autoimmune thyroid diseases. Although scientific evidence supports selenium’s critical functions in hormone metabolism and antioxidant protection, public awareness and monitoring of selenium intake remain insufficient. Beyond the need for further research, there is an urgent call for integrated public health strategies, ranging from sustainable, food-based approaches to targeted clinical screening and educational programs. Promoting awareness of selenium’s importance and incorporating selenium status into maternal and pediatric care protocols could play a significant role in preventing deficiencies and supporting long-term endocrine and neurodevelopmental health.