Exercise and Iodine Deficiency

Although it is standard practice to replace fluid and electrolytes lost during vigorous exercise, replacement requirements seldom exist for minerals such as iodine. Iodine is an essential component for the production of thyroid hormones; hence, inadequate dietary intake leads to diminished thyroid hormone levels. On the basis of the published sweat iodine content of 35–40 μg/l and a potential sweat loss of 4–5 liters following vigorous exercise, daily iodine losses in sweat equivalent to the WHO-recommended adult daily intake (150 μg) might be expected. When added to urinary iodine excretion, such losses would result in a significant diminution in the body's iodine stores. Previous reports have suggested that sweat iodine content is independent of dietary intake, but data indicate that this may only apply with replete iodine status. As a published sweat iodine concentration of 35–40 μg/l sweat losses of 4–5 liters would involve iodine losses equivalent to the WHO-recommended adult daily iodine intake (∼150 μg). Iodine losses in sweat may not be independent of dietary iodine intake. Over a prolonged period of exercise, sweat iodine losses would result in a significant depletion of thyroidal iodine stores.