by Richard Aiken MD PhD
Iodine, an essential nutrient, is an intrinsic component of the thyroid hormone regulating metabolism at all ages and critical for fetal, infant, and child development, including neurodevelopment[1] .
Iodine deficiency is the leading cause of preventable intellectual developmental disability in the world. If iodine intake is chronically too low or too high, prevalence of hypothyroidism and hyperthyroidism may be elevated[2].
The daily Dietary Reference Intake (DRI) recommended by the United States Institute of Medicine is between 110 and 130 µg for infants up to 12 months, 90 µg for children up to eight years, 130 µg for children up to 13 years, 150 µg for adults, 220 µg for pregnant women and 290 µg for lactating mothers[3]. The Tolerable Upper Intake Level for adults is 1,100 μg /day (1.1 mg/day).
Hypothyroidism results in symptoms that appear similar to clinical depression, such as low mood, low energy levels, weight gain, forgetfulness, and personality changes; it can also lead to elevated cholesterol levels.
Hyperthyroidism mimics mania and anxiety disorders, with increased activity and weight loss, difficulty sleeping, and irritability.
Reduction in the prevalence of iodine deficiency worldwide has been achieved through the fortification of sodium chloride (“table salt”; sea salt and salted processed foods are not fortified with iodine), but salting foods leads to increase in blood pressure, the major risk factor for death worldwide. Therefore, if we are not eating salted food or fish, as recommended in our whole-food varied plant diet, are we getting enough iodine?
In fact, making the dietary iodine sufficiency even more challenging, soy, flaxseeds, spinach, sweet potatoes, pears, peaches, raw cruciferous vegetables (broccoli, Brussels sprouts, cauliflower, and cabbage) and other fruits and vegetables disrupt the production of thyroid hormones by interfering with iodine uptake in the thyroid gland[4], acting as so-called goitrogens.
There are fruits and vegetables that may contain significant levels of iodine, but this is highly dependent on the soil from which the plant was grown. Organic farming tends to yield higher amounts of iodine because there is a greater tendency for proper soil management and crop rotation. Some foods that may contain significant amounts of iodine include:
Dried seaweed; a quarter ounce serving may contain as much as 4500 µg of iodine – four times the Tolerable Upper Intake Level. Unless you are a regular consumer of high purity seaweed and can adjust the amount to close to the DRI, this should probably not be your dietary source of iodine.
Potatoes; the skin of a medium size common potato can harbor as much as 60 µg of iodine, so three potatoes could provide adequate daily intake. However, again, it depends on the soil and farming methods as well as the accompanying dietary goitrogens.
Cranberries; can be rich in iodine with the same provisos as those listed for potatoes.
There are limited data on the dietary iodine intake of vegetarians and vegans in the United States; however, the iodine content of a Swedish vegan diet was found to be 39 µg iodine per 1000 kcal compared to a mixed diet of 156 µg[5] per 1000 kcal. This was similar to the iodine content of German vegan diets[6].
The first report of iodine nutrition and thyroid function in vegans in the United States stated that Americans are at risk for low iodine intake, and these were for vegans that did allow use of iodine-enriched sodium chloride.
Therefore, for those individuals with whole-food varied-plant dietary patterns not using iodine-enriched sodium chloride, an iodine supplement is recommended. An example supplement of potassium iodide contains 225 µg[7].
References
[1] Delange, F. (2007). Iodine requirements during pregnancy, lactation and the neonatal period and indicators of optimal iodine nutrition. Public Health Nutrition, 10(12A). doi:10.1017/ s1368980007360941.
[2] Zimmermann, M. B., & Boelaert, K. (2015). Iodine deficiency and thyroid disorders. The Lancet Diabetes & Endocrinology, 3(4), 286-295. doi:10.1016/s2213-8587(14)70225-6.
[3] United States National Research Council (2000). Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. National Academies Press. pp. 258–259.
[4] Vanderpas J (2006). “Nutritional epidemiology and thyroid hormone metabolism”. Annu. Rev. Nutr. 26: 293–322. doi:10.1146/annurev.nutr.26.010506.103810.
[5] AbdullaM, Andersson I, Asp NG, Berthelsen K, Birkhed D, Dencker I, Johansson CG, Ja¨ gerstad M, Kolar K, Nair BM, Nilsson-Ehle P, Norde´n A, Rassner S, Akesson B, Ockerman PA (1981) Nutrient intake and health status of vegans. Chemical analyses of diets using the duplicate portion sampling technique. Am J Clin Nutr 34:2464 – 2477.
[6] Waldmann A, Koschizke JW, Leitzmann C, Hahn A 2003 Dietary intakes and lifestyle factors of a vegan population in Germany: results from the German Vegan Study. Eur J Clin Nutr 57:947–955.
[7] As an example, Pure Encapsulations – Iodine (potassium iodide) – Hypoallergenic Supplement contains capsules of 225 µg at a daily cost of $0.12 per capsule.