Iodine is a trace element, which means that a dog's body needs it only in trace amounts. Despite this, its role cannot be overestimated. Meat and offal alone in a BARF diet are not sufficient to meet the requirement for this element, so supplementation is generally necessary, preferably with products based on ingredients of natural origin. It is important to always remember to calculate the appropriate dose for our four-legged companion precisely, based on FEDIAF guidelines and NRC standards, because both excess iodine and iodine deficiency can be dangerous to health.
What functions does iodine perform?
Iodine is primarily a component of thyroid hormones such as thyroxine (T4) and triiodothyronine (T3). These hormones perform many important functions in the body. They are responsible for proper thermoregulation and regulate metabolism. Their role in reproductive processes is essential. They also participate in the functioning of the circulatory and muscular systems. They are highly important in young animals, ensuring proper growth as well as physical and mental development. This is associated with their effects on the pituitary gland and gonads. They are also necessary for tissue differentiation and maturation. Iodine also helps maintain healthy skin and coat condition.
Regulation of blood concentration
Iodine is regularly taken up by the thyroid gland through active transport. Thanks to this mechanism, when intake is adequate, its supply is maintained at a more or less constant level, although the iodide content of blood plasma varies. Thyroid-stimulating hormone (TSH), released by the pituitary gland, also participates in regulating iodine uptake by thyroid cells. In addition, the activity of thyroid hormones is controlled by neurotransmitters, hormones, and enzymes in the central nervous system, pituitary gland, circulatory system, and peripheral tissues.
Is supplementation necessary?
Iodine requirements depend on the dog's physiological state and diet. They increase in female dogs during lactation because the body loses about 10% of the trace element in milk. With regard to diet, iodine intake must be higher when the diet contains relatively large amounts of goitrogenic substances (so-called goitrogens), which hinder iodine absorption and disrupt thyroid function. They are found in peas, peanuts, soy, and flaxseed. Iodine supplementation is also often indicated when there is an excess of certain minerals in the diet, such as arsenic, bromides, fluorides, cobalt, potassium, calcium, or manganese. The appropriate iodine level required by our animal is best determined on the basis of FEDIAF guidelines and NRC standards. For animals that are ill, it is best to consult a veterinarian to avoid the risk of adverse effects resulting, for example, from interactions with other supplements or medications. It is easy to overdo dietary iodine supplementation because products of natural origin are often used, most commonly those based on Kelp algae, in which the concentration of the element may vary from batch to batch. This depends, among other factors, on the time or place of harvesting, the level of contamination in the body of water, or the part of the organism from which they originate. Therefore, the composition stated on the specific packaging should always be read carefully.
Dietary sources
Meat and offal are moderate dietary sources of iodine and will not be sufficient on their own to meet the requirement. Richer sources include marine fish, eggs, and iodized salt. Supplements based on Kelp seaweed are very commonly given; they have a very high iodine content, but, as mentioned above, it is also variable.
What does an insufficient amount of iodine in the diet cause?
Iodine deficiency in the diet causes thyroid dysfunction and insufficient production of the hormones T3 and T4, which means hypothyroidism, a condition diagnosed fairly rarely in dogs. However, it may occur in dogs fed a BARF diet with no supplementation or with inadequate supplementation, and such cases have been confirmed. Bilateral enlargement of the thyroid lobes and a slight increase in body weight were observed in these cases. Once an adequate dietary iodine supply was provided, the thyroid returned to normal function. Too little iodine in the diet of a pregnant or lactating female dog can cause developmental disorders in the offspring.
Can iodine be overdosed?
Unfortunately, careless supplementation can easily result in an iodine overdose. An excessively high concentration can also cause functional thyroid problems and hypothyroidism. The symptoms are not always immediately noticeable. They depend on the animal's age and health, as well as the dose and the length of time the body is exposed to excess iodine. They include apathy, reduced activity, weight gain unrelated to the diet, and poorer tolerance of cold. Coat condition deteriorates. An iodine overdose can be particularly risky in puppies, whose hormonal system is highly sensitive.
Sources
- Wedekind, K. J., Yu, S., Kats, L., Paetau-Robinson, I., & Cowell, C. S. (2010). Micronutrients: Minerals and vitamins. W 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.
- Lim, S., Sohn, S.-J., & Hong, Y.-J. (2026). Case report: Diet-associated iodine-deficiency goitrous hypothyroidism in a dog: A longitudinal clinical, endocrine, and ultrasonographic evaluation. Frontiers in Veterinary Science, 13, Article 1761152.
- Castillo, V. A., Lalia, J. C., Junco, M., Sartorio, G., Márquez, A., Rodriguez, M. S., & Pisarev, M. A. (2001). Changes in thyroid function in puppies fed a high iodine commercial diet. The Veterinary Journal, 161(1), 80–84.