Kelp, a large seaweed from the brown algae category (order Laminariales), provides the richest source of naturally occurring iodine.1 It is one of those products that seems innocuous but can in fact be dangerous due to its high and somewhat unpredictable iodine content.2 Ingested iodine affects thyroid function, whether it originates from food, dietary supplements, Chinese herbal mixtures or drugs. Medical sources of excessive iodine include pharmaceuticals (such as amiodarone), radiology contrast agents and topical antiseptics. Ads for kelp supplements for dogs boast its benefits for vitality, immunity and “proper function of the thyroid gland.”3 Kelp often appears as a heavily promoted dietary ingredient included in home-prepared raw diets. However, considering the inclination of many to believe that “more is better,” the sum total of iodine ingested day after day from both supplemental and dietary sources may prove detrimental to an animal’s thyroid status and health. ‘Inactive Ingredient’ Kelp might also show up as an “inactive ingredient” in products such as selenium supplements, although the amount of iodine from batch to batch can vary considerably.4 No matter the source, these Laminaria macro algae may interfere with thyroid replacement treatment, negatively affect patients with pre-existing thyroid disorders, or upend an otherwise euthyroid status.5-6-7 For example, a 39-year-old woman with all multinodular goiter was prescribed an herbal tea with large amounts of kelp, Sargassum weed, and kombu by a Chinese medicine practitioner. The herbal mixture produced an iodine-induced thryrotoxicosis requiring antithyroid drug therapy.8 The authors of this case report advised, “[P]atients with known thyroid disease should be advised to avoid all complementary and alternative medications that contain iodine.”9 Nevertheless, Chinese herbs with sargassum and laminaria are promoted for dogs, cats, and horses with hyperthyroidism, though with undisclosed amounts of iodine-laden ingredients.10-11 Kelp-heavy diets, promoted as weight loss approaches for humans, have been shown to cause “myxedema,”12a manifestation of hypothyroidism characterized by dry skin and waxy, non-pitting edema around the lips and nose, frequently accompanied by deterioration in mental acuity and decreased physical activity. Thyroid Effects Kelp can actually lead to either hypothyroidism or hyperthyroidism depending on the patient’s thyroid hormone metabolism. Discontinuation of the product may or may not resolve the problem. Ingesting kelp along with levothyroxine medication or other thyroid replacement may result in hyperthyroidism or thyrotoxicosis.13 Concerns about kelp supplementation causing thyroiditis or other problems have circulated within the veterinary community for years, but little work has been done to document cause and effect in dogs and cats. In contrast, reports linking kelp to endocrine abnormalities have accumulated in the human medical literature over the past decade. The thyroid gland possesses intrinsic autoregulatory mechanisms to cope with excess amounts of circulating iodine, but large quantities can temporarily inhibit the oxidation process of iodine, which is the essential first step in producing thyroid hormone.14 This inhibitory process, known as the acute Wolff-Chaikoff effect, is overcome after about 48 hours in humans, allowing thyroid hormone synthesis to normalize. However, patients with underlying thyroid abnormalities may fail to execute a successful “escape” from the Wolff-Chaikoff effect, and succumb to either hypo- or hyperthyroidism in response to iodide excess. At least in humans, these two disparate outcomes relate to differences in the sensitivity to the iodine-related inhibition of hormone biosynthesis.15 In other words, patients with hypersensitivity to the turn-off become hypothyroid, while those with lowered sensitivity enter a hyperthyroid state. Recommendations The recommended daily allowance (RDA) for human iodine intake ranges from 40 micrograms (mcg) to 200 mcg. The RDA of iodine for most animals is unknown; one source reports it to be approximately 15 mcg/kg daily for dogs and 100 mcg per day for cats.16 The amount of iodine in kelp supplements varies, but often reaches in the tens to hundreds of times the RDA for any species.17 The risks of herbal kelp supplements are not limited to merely their iodine content. A case of potential arsenic toxicosis secondary to a kelp supplement prompted public health researchers to investigate the extent of arsenic contamination in commercially available kelp products, analyzing nine samples randomly obtained from health food stores in California.18 They found detectable levels of arsenic, higher than the Food and Drug Administration’s tolerance level of 0.5 to 2 ppm, in eight of the nine representative products. None of the supplements contained warnings on their labels that the supplements could be contaminated with arsenic or other heavy metals. Chronic arsenic toxicity affects the peripheral and central nervous systems, leading to peripheral neuropathies, cognitive deficits, muscular weakness, hepatomegaly, gastrointestinal complaints, skin abnormalities, diffuse alopecia and subcutaneous edema.19 As noted by the authors, “It is unfortunate that a therapy which is advertised (on the label) as contributing to ‘vital living and well-being’ would have potentially unsafe levels of arsenic.” They conclude, “Given the numerous studies demonstrating unsafe levels of heavy metals in dietary herbal preparations, the growing number of case reports connecting heavy metal toxicities to ingestion of herbal dietary supplements, and the growing popularity of herbal remedies for self-medication in the general public, it is prudent that companies demonstrate safety and efficacy before their products are placed on the market. Concentrations of materials contained in the preparations, as well as expected benefits and potential side effects, should be studied, standardized, and accurately labeled.” 20 Dr. Robinson, DVM, DO, Dipl. ABMA, FAAMA, oversees complementary veterinary education at Colorado State University. <HOME> FOOTNOTES 1. Martinelango PK, Tian K, and Dasgupta PK. Perchlorate in seawater, bioconcentration of iodide and perchlorate by various seaweed species. Analytica Chimica Acta. 2006;567:100-107. 2. Mussig K, Thamer C, Bares R, et al. Case report. Iodine-induced thyrotoxicosis after ingestion of kelp-containing tea. J Gen Intern Med. 2006;21:C11-C14. 3. The Dog Bowl. Kelp for dogs. Obtained at http://www.thedogbowl.com/PPF/category_ID/0_71/dogbowl.asp on 02-20-11. 4. Arum SM, He X, and Braverman LE. Excess iodine from an unexpected source. N Engl J Med. 2009;360(4):424-426. 5. Miller LG. Herbal Medicinals. Selected clinical considerations focusing on known or potential herb-drug interactions. Arch Intern Med. 1998;158:2200-2211. 6. Shilo S and Hirsch HJ. Iodine-induced hyperthyroidism in a patient with a normal thyroid gland. Postgraduate Medical Journal. 1986;62:661-662. 7. Clark CD, Bassett B, and Burge MR. Effects of kelp supplementation on thyroid function in euthyroid subjects. Endocrine Practice. 2003;9(5):363-369. 8. Mussig K, Thamer C, Bares R, et al. Case report. Iodine-induced thyrotoxicosis after ingestion of kelp-containing tea. J Gen Intern Med. 2006;21:C11-C14. 9. Mussig K, Thamer C, Bares R, et al. Case report. Iodine-induced thyrotoxicosis after ingestion of kelp-containing tea. J Gen Intern Med. 2006;21:C11-C14. 10. Xie H. Chinese Veterinary Herbal Handbook, 2nd edition. Chi Institute of Chinese Medicine, pp. 99-100. 11. Dr. Xie’s Jing-Tang herbal Inc. Quick selection of Chinese herbal formulas based on clinical conditions. Obtained at http://www.tcvm.com/doc/handbook.pdf on 022011. P. 23 12. Miller LG. Herbal Medicinals. Selected clinical considerations focusing on known or potential herb-drug interactions. Arch Intern Med. 1998;158:2200-2211. 13. Miller LG. Herbal Medicinals. Selected clinical considerations focusing on known or potential herb-drug interactions. Arch Intern Med. 1998;158:2200-2211. 14. Mussig K, Thamer C, Bares R, et al. Case report. Iodine-induced thyrotoxicosis after ingestion of kelp-containing tea. J Gen Intern Med. 2006;21:C11-C14. 15. Mussig K, Thamer C, Bares R, et al. Case report. Iodine-induced thyrotoxicosis after ingestion of kelp-containing tea. J Gen Intern Med. 2006;21:C11-C14. 16. Riviere JE and Papich MG. Veterinary Pharmacology and Therapeutics, 9th edition. Wiley and Sons, 2009, p. 736. 17. Teas J, Pino S, Critchley A, et al. Variability of iodine content in common commercially available edible seaweeds. Thyroid. 2004;14(10):836-841. 18. Amster E, Tiwary A, and Schenker MB. Case report: Potential arsenic toxicosis secondary to herbal kelp supplement. Environ Health Perspect. 2007;115:606-608. 19. Amster E, Tiwary A, and Schenker MB. Case report: Potential arsenic toxicosis secondary to herbal kelp supplement. Environ Health Perspect. 2007;115:606-608. 20. Amster E, Tiwary A, and Schenker MB. Case report: Potential arsenic toxicosis secondary to herbal kelp supplement. Environ Health Perspect. 2007;115:606-608.
