Kelp is part of a broader group of seaweeds/algae that have become popular ingredients in dog and cat supplements, home-prepared petfoods, raw petfoods and specialty or boutique petfoods. Seaweeds/algae are a rich source of:

• Minerals such as calcium and iron;
• Vitamins such as folic acid;
• Antioxidants such as alpha- and beta-carotene;
• Omega-3 fatty acids such as alpha-linolenic acid and eicosapentaenoic acid; and
• The flavor-enhancing amino acid glutamate.

Despite these benefits, the trace mineral iodine is the main reason for adding kelp. Is it a viable source of iodine?

Iodine nutrition

Iodine was one of the first recognized essential nutrients due to its connection with a very visual, disfiguring disease called goiter. Goiter appears as an enlargement of the thyroid gland in the neck. References to goiter and its treatment with herbs and seaweed date back some 4,000 to 5,000 years.

At the core of this disease is a disruption in the normal attachment of iodine to tyrosine in the formation of the thyroid hormones thyroxine (T4) and triodothyronine (T3). These hormones serve as the body's thermostat, regulating metabolism and physiology. Deficiencies can result in retarded physical and mental development, arrested adrenal and gonadal development, obesity, incoordination, dermatitis and hair loss (alopecia), to name but a few problems.

Hypothyroidism

To be effective, iodine goes through a series of oxidation states. In nature, iodine occurs most commonly as iodide (I-), elemental iodine (I2) and iodate(IO3-). Following ingestion, iodine and iodate are reduced to iodide, then absorbed and circulated throughout the body. Circulating iodide is trapped by the thyroid and oxidized by thyroid peroxidase to iodine for attachment to tyrosine.

If iodine is insufficient or if antagonists to normal iodination of tyrosine are present (goitrogens), then a hormone overstimulates the thyroid gland in an effort to maintain the body in a normal state. It's actually a hypothyroid state: The thyroid overworks to produce thyroid hormones and becomes enlarged as it tries to regulate the body's normal functioning. Hypothyroidism is one of the most commonly diagnosed endocrine diseases. If the cause is insufficient dietary iodine or goitrogens, it can usually be treated successfully.

Kelp contains some of the highest amounts of iodine, but it can vary greatly. - Greg Aldrich

From seaweeds/algae

The iodine content of seaweeds/algae is quite variable and depends on species, location, season, plant part, harvesting method and storage conditions. Of the edible seaweeds/algae, kelp (primarily Laminaria) contains some of the highest naturally occurring amounts of iodinein the range of 1,542 to 5,307 parts per million (ppm) with an average of 2,990 ppm (Teas et al., 2004). This iodine is predominately water soluble and, since most (about 88%) is in the iodide form, it's subject to oxidation during drying and exposure to sunlight.

Kelp is an acceptable source of iodine in the diet, though reports on bioavailability in animals is lacking. Since dried kelp is sold in a free flowable powder, it can be easily handled. But given its ability to oxidize, kelp should be stored in protective packaging, avoiding extremes in heat and direct sunlight.

For the petfood label

Kelp is a more variable, volatile and less cost effective form of iodine than standard sources such as potassium iodide, calcium iodate or ethylenediamine dihydriodide. Thus, the motivation to incorporate kelp in the diet has to be driven by a consumer-based message of delivering iodine in a unique form or a deliberate effort to reduce the number of chemical sounding descriptors on the ingredient panel.

The names currently approved by the Association of American Feed Control Officials for these ingredients are relatively consumer friendly:

• [60.76] "Dried Seaweed Meal is the product resulting from drying and grinding non-toxic macroscopic marine algae (marine plants) of the following botanical divisions: Division RHODOPHYTA (Red Algae); Division PHAEOPHYTA (Brown Algae); Division CHLOROPHYTA (Green Algae)."
• [60.19] "Dried Kelp is dried seaweed of the families Laminariacae and Fucaeaesold as a source of iodine (I), the minimum percentage of iodine must be declared."

Mixing it all together

Although the iodine requirements of dogs and cats is presumed to be small (ppm), balancing dietary requirements is not trivial. This is because the iodine content of base ingredients used in petfoods is seldom reported or measured. So the starting point for balancing iodine levels is often assumed to be zero.

Meeting daily requirements, therefore, depends on supplemental sources: just enough, but not too much. Because kelp carries a suitable level of iodine, it can certainly fulfill the role. However, the iodine content of kelp can vary greatly and at the extreme high-end of the range could be considered a goitrogen. Further, kelp can bio-concentrate more than just iodine; for example, toxic levels of arsenic have also been noted.

Petfood companies should use kelp only with much skepticism about its iodine content and level of contaminates. When sourcing, verify the iodine and contaminate content. If that condition is met, kelp can be a viable source of iodine in pet diets.