Iodine in biology
The U.S. Food and Nutrition Board and Institute of Medicine recommended daily allowance of iodine ranges from 150 micrograms per day for adult humans to 290 micrograms per day for lactating mothers. However, the thyroid gland needs no more than 70 micrograms per day to synthesize the requisite daily amounts of T4 and T3. The higher recommended daily allowance levels of iodine seem necessary for optimal function of a number of other body systems, including lactating breasts, gastric mucosa, salivary glands, oral mucosa, arterial walls, thymus, epidermis, choroid plexus and cerebrospinal fluid, among others.
Puppy nutrition
To date, there is little information available about minimum requirements of dietary iodine for developing puppies. However, literature suggests that overdosage of iodine in puppies has deleterious effects on the thyroid gland. High dietary iodine may cause both hypothyroidism and changes in bone metabolism, considering that thyroid hormones are key factors in osteogenesis, as they stimulate osteoblasts, and promote collagen synthesis and mineralization of the osteoid. This is particularly important during juvenile development, as these hormones favor the action of growth hormone (GH) and its facilitator, insulin growth factor-1 (IGF-1) at the osteoplastic level. Hypothyroidism acquired at an early age presents a delay in the maturation and development of the ossification sites of newly-developing bone. It is therefore important to closely monitor the amount of iodine in puppy diets in order to prevent overdosage. The NRC states an adequate intake and recommended allowance of 900 μg/kg (DM) which translates into 220μg/1000 kcal. These values have been shown in multiple studies to be the recommended maximum allowance of iodine that would result in no abnormalities.