What It Does
The thyroid gland needs iodine to produce thyroid hormones (T3 and T4), which regulate your pet's entire metabolism — body temperature, heart rate, growth, and energy levels. Without enough iodine, the thyroid can't function properly, leading to hypothyroidism.
What You’ll Notice
Iodine deficiency causes the same symptoms as hypothyroidism: weight gain, lethargy, cold intolerance, dry skin, and thinning coat. In pregnant animals, deficiency can cause stillbirths or weak puppies/kittens. Excess iodine is also harmful — it paradoxically suppresses thyroid function.
Sources & Notes
Fish, seaweed, iodized salt, dairy. Commercial pet foods are formulated with adequate iodine. Raw or homemade diets without seafood may be deficient. Kelp supplements are sometimes used but can easily cause excess.