Iodine is an essential building block of the thyroid hormones thyroxine and triiodothyronine, which act on the pituitary gland and gonads. These hormones regulate metabolic rate, body temperature, heart function and the nervous and muscular systems, and support normal growth and development in puppies and kittens [1]. They also enable tissue differentiation. Thyroid uptake of iodine from blood plasma is regulated, among other factors, by thyroid-stimulating hormone [2].
What it contains: Seaweed (kelp), marine fish (cod, pollock and saithe) and eggs [1]. In raw diets, pay particular attention to the iodine level. Iodine content in kelp is extremely variable, so careless supplementation can cause either excess or, when food provides no source, deficiency [5].
Deficiency: It is practically absent in animals fed commercial food (which contains added potassium iodide, calcium iodate or potassium iodate). It is easy to develop in a poorly balanced home diet without iodine-rich foods, because meat and bones contain extremely little of this element. This causes hypothyroidism (the animal becomes apathetic, seeks warm places and gains weight quickly), dermatological problems (dry, brittle, dull fur) and endemic goitre (an enlarged thyroid visible on the neck) [1] [3].
Excess: Dogs and cats have fairly low tolerance for excess iodine. It most often results from uncontrolled supplement use by the caregiver. Long-term excessive supplementation can paradoxically block thyroid function, causing a dog to show symptoms identical to iodine deficiency [4].
Sources
- National Research Council (2006). Nutrient Requirements of Dogs and Cats. National Academies Press. https://nap.nationalacademies.org/catalog/10668/nutrient-requirements-of-dogs-and-cats
- Wedekind, K. J., Yu, S., Kats, L., Paetau-Robinson, I., & Cowell, C. S. (2010). Micronutrients: Minerals and vitamins. In M. S. Hand, C. D. Thatcher, R. L. Remillard, P. Roudebush, & B. J. Novotny (Eds.), Small Animal Clinical Nutrition (5th ed., Chapter 6). Mark Morris Institute. https://www.markmorrisinstitute.org/sacn5_download.html
- Merck Veterinary Manual. Goiter in Animals. https://www.merckvetmanual.com/endocrine-system/the-thyroid-gland/goiter-in-animals
- Edinboro CH, Scott-Moncrieff JC, Glickman LT (2010). Feline Hyperthyroidism: Potential Relationship with Iodine Supplement Requirements of Commercial Cat Foods. https://pmc.ncbi.nlm.nih.gov/articles/PMC11149000/
- Assessment of mineral adequacy in prepared raw dog foods labeled as complete (2025). Scientific Reports. https://pmc.ncbi.nlm.nih.gov/articles/PMC12690097/