Iodine and thyroid function: Implications for metabsolism and performance in athletes

Iodine is a vital micronutrient that underpins thyroid hormone synthesis, affecting myriad physiological processes that extend well beyond basic metabolism. In athletes, an optimal level of thyroid hormones particularly triiodothyronine (T₃) and thyroxine (T₄) is integral to energy production, thermoregulation, macronutrient metabolism, and muscle recovery. Despite well-publicized global efforts to reduce iodine deficiency through measures such as salt iodization, suboptimal iodine status still persists, including in populations that might be assumed healthy and nutritionally aware. Athletes are especially vulnerable due to higher nutrient turnover, specialized diets, and additional micronutrient losses through sweat. Even marginal deficiencies can attenuate the benefits of training and potentially impair athletic performance, manifesting as increased fatigue, reduced aerobic capacity, or prolonged recovery intervals.
The purpose of this review is to present a comprehensive examination of the nexus between iodine and thyroid function, with particular emphasis on the metabolic and performance implications for athletes. We begin by outlining key aspects of iodine physiology, tracing the pathway from dietary intake through the sodium-iodide symporter (NIS) and culminating in the synthesis of T₃ and T₄ within the thyroid gland. Next, we examine the mechanisms of the hypothalamic-pituitary-thyroid (HPT) axis and highlight how even subtle imbalances in iodine intake may provoke disruptions in thyroid-stimulating hormone (TSH), leading to subclinical or overt hypothyroidism.
Empirical findings on the influence of exercise on iodine turnover and thyroid hormone dynamics receive close attention, revealing a bidirectional relationship wherein high-intensity or high-volume training can alter thyroid homeostasis, while inadequate iodine status exacerbates performance deficits. The review further explores typical dietary sources of iodine, recommended intake levels for adult populations, and the ways in which these guidelines may need to be adjusted for athletes with elevated needs. Strategies for supplementation are presented alongside cautions regarding excessive iodine intake, which can lead to hyperthyroidism, thyroid autoimmunity, or goiter.
By synthesizing evidence from clinical, epidemiological, and performance-based research, this review underscores how iodine sufficiency is critical for maximizing metabolic efficiency and physical potential. Coaches, athletes, and sports health professionals are therefore urged to incorporate monitoring of iodine status alongside other key micronutrients into comprehensive nutrition and training programs designed to foster peak performance over the long term.