With the growing urgency to address environmental sustainability, many dietary recommendations now advocate for plant-based diets. The primary sources of iodine—fish, eggs, and dairy products— come from animal sources. Therefore, a critical question arises: can plant-based diets provide enough iodine? This is especially important because iodine, essential for thyroid hormone production, plays a vital role in growth, brain development, and cognitive function, particularly during pregnancy and early life. Data from the National Diet and Nutrition Survey reveals a significant decline in the consumption of iodine-rich foods, especially milk, alongside a rise in plant-based alternative consumption (Chapter 3). While this shift aligns with global recommendations to reduce animal-source food consumption, without fortification of plant-based foods, adherence to plant-based dietary recommendations would lead to widespread iodine insufficiency (Chapter 4). This is a concern as only a small percentage of plant-based alternatives are fortified with iodine, and even fortified products often provide lower iodine content than cow’s milk products (Chapter 5). Replacing milk with unfortified plant-based alternatives results in a substantial reduction in iodine intake, particularly among young children who rely heavily on milk as a source of iodine (Chapter 6). However, fortifying all plant-based alternatives to an industry standard or adding iodised salt to bread could effectively compensate for this iodine deficit, as shown by simulation scenarios (Chapter 7). Consequently, a tool designed to identify those at risk of thyroid dysfunction due to insufficient iodine intake, particularly plant-based milk consumers, is crucial for detecting early signs of iodine insufficiency and mitigating the risks associated with iodine deficiency (Chapter 8). The findings of this thesis underscore the importance of iodine fortification in plant-based foods and robust public health initiatives to safeguard against iodine deficiency, ensuring that a shift toward plant-based diets does not come at the expense of public health.