Iodine

Iodine is a trace element indispensable to the production of thyroid hormones, which govern energy metabolism, growth and many other functions; iodine is literally built into the structure of those hormones. Its balance is unusually delicate, because both too little and too much disturb the thyroid. Prolonged deficiency can lead to hypothyroidism and an enlarged gland, or goitre, with a slowed metabolism, weight gain and coat problems. Chronic excess is just as problematic and has been discussed as a possible contributing factor in thyroid disease, notably feline hyperthyroidism, one of the most common conditions of older cats, whose cause remains multifactorial (NRC, 2006). For this reason a complete food is formulated to a cautious intake window, neither too low nor too high. Iodine sources include seafood, fish and certain seaweeds, whose content can vary enormously, which is one reason seaweed-heavy supplements can unintentionally overshoot. A striking therapeutic application turns the nutrient on its head: cats with hyperthyroidism can be managed with a prescription diet so strictly limited in iodine that the overactive thyroid cannot make excess hormone, used under veterinary supervision. Iodine illustrates why the cat features so heavily in mineral discussions. See the [Petipedia glossary](/glossary) for related trace minerals.

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