High Iodine Content of Korean Seaweed Soup: A Health Risk for Lactating Women and Their Infants?

Abstract

Iodine requirements increase during pregnancy and lactation due to increased maternal thyroid hormone production and iodine excretion, fetal iodine requirements, and loss of iodine in breast milk. Seaweed preparations are a source of dietary iodine. Korean and many Korean-American women traditionally consume brown seaweed soup (Undaria pinnatifida) daily during the early postpartum period (Supplementary Data; Supplementary Data are available online at www .liebertonline.com/thy) (1). This tradition is maintained among Korean and Korean-American women such that their breast milk iodine correlates strongly with frequency and quantity of seaweed soup consumption (2,3). As the iodine content of this soup has not been reported, we randomly selected 10 brands of dried brown seaweed from Korea and China available in the United States. Seaweed soup from each brand was prepared utilizing the following ingredients: 1 oz of dried seaweed, 6 cups water, ¼ pound beef, 1½ tablespoons soy sauce, 2 teaspoons sesame oil, 1 teaspoon garlic, and *½ teaspoon noniodized sea salt (Supplementary Data). Iodine content of the dried seaweeds and the soups were measured spectrophotometrically after digestion with hydrochloric acid and dilution with iodine free deionized water, as described byThe mean iodine content of the dried seaweed was 359 AE 254 mg/g (mean AE SD), or 10173 AE 7200 mg/oz. The mean iodine content of seaweed broth was 1.9 AE 0.7 mg/mL, with 1 bowl (250 mL) of broth containing an average of 487 AE 178 mg of iodine. The mean iodine content of blended seaweed soup contents (broth, cooked seaweed) was 1705 AE 930 mg/250 mL. Potential sources of variability in soup iodine (see Supplementary Data) include the iodine contents of dry seaweed and other ingredients (e.g., iodized salt, iodine-containing soy sauce, and anchovy soup base), cooking methodologies, and the quantity of seaweed in recipes (4). The iodine content of seaweed varies with harvest location and season, salinity and temperature of water, depth and portion of seaweed harvested, and storage conditions (4).The World Health Organization (WHO) guidelines recommend 250 mg/day of iodine intake during pregnancy and lactation, whereas the Institute of Medicine (IOM) recommends 220 mg/day of iodine intake during pregnancy and 290 mg/day during lactation (Supplementary Data). The IOM recommends a tolerable upper limit of iodine intake of 1100 mg/day, whereas the WHO suggests an upper limit of 500 mg/day for pregnant and lactating women and 180 mg/ day for infants. More than 90% of postpartum lactating Korean women consume seaweed soup at least three times daily in the first postpartum week, and up to 75% of these women have seaweed soup at least once daily up to 4 weeks postpartum (3). Our findings indicate that this constitutes an average iodine intake of at least 1400 mg/day in the first postpartum week based solely on 250 mL seaweed soup broth three times daily, and at least 5000 mg/day if the entire contents of each serving are consumed (broth and seaweed). High level...

Comparison of two sources of iodine delivery on breast milk iodine and maternal and infant urinary iodine concentrations in southern Ethiopia: A randomized trial

“…Although there was wide range in both BMIC and UIC, there were few concerningly high values in response to either iodized salt or iodine capsule and no adverse reaction was reported in any of the study participants. In a study of 50 Korean women, whose diets frequently included seaweed soup, considerable elevation and range of BMIC from 198 to 8484 μg/L was reported (Rhee, Braverman, Pino, He, & Pearce, ). Significant variation of BMIC ranging from 5 to 2170 μg/L (Dorea, ) and from 9 to 1267 μg/L (Semba & Delange, ) were also reported in two other reviews.…”

Excess iodine intake: sources, assessment, and effects on thyroid function

“…Breast milk is the principal route to assure infant iodine intakes in both exclusively breastfed infants and those also receiving complementary foods (see above). Mothers with excessive iodine intake typically have a high BMIC . Excess iodine consumption during lactation may not only increase the maternal susceptibility to thyroid dysfunction, but case reports also suggest the risk of subclinical and clinical hypothyroidism in their infants induced by excess BMICs .…”

Consequences of excess iodine

“…Seaweed is a popular food item in many parts of the world, particularly in Japan 34 and other Asian countries, where ingestion of seaweed soup is common in the everyday diet and is a frequent practice during the postpartum period. 35 However, the iodine content of seaweed can vary widely. 36 Cases of kelp-induced thyrotoxicosis have been widely reported, including one woman who drank kelp-containing tea for 4 weeks 37 and another patient who had a long-standing history of using kelp-containing dietary supplements.…”