• Nutrition Research and Practice
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• 제18권3호
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• pp.412-424
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• 2024

BACKGROUND/OBJECTIVES: Although iodine is essential for thyroid hormone production and controls many metabolic processes, there are few reports on the iodine intake of the population because of the scarcity of information on the iodine content in food. This study estimated the iodine intake of Koreans from brown seaweed, the major source of iodine in nature. SUBJECTS/METHODS: The dietary intake data from the recent Korea National Health and Nutrition Examination Survey (2016-2021) and the iodine content in brown seaweed were used for the estimation. Nationwide brown seaweed samples were collected and prepared using the representative preparation/cooking methods in the Koreans' diet before iodine analysis by alkaline digestion followed by inductively coupled plasma mass spectrometry. RESULTS: The mean (± SE) iodine intake from sea mustard was 96.01 ± 2.36 ㎍/day in the Korean population. Although the iodine content in kelp was approximately seven times higher than that in sea mustard, the mean iodine intake from kelp (except broth) was similar to that of sea mustard, 115.58 ± 7.71 ㎍/day, whereas that from kelp broth was 347.57 ± 10.03 ㎍/day. The overall mean iodine intake from brown seaweed was 559.16 ± 13.15 ㎍/day, well over the Recommended Nutrient Intake of iodine for Koreans. Nevertheless, the median intake was zero because only 37.6% of the population consumed brown seaweed on the survey date, suggesting that Koreans do not consume brown seaweed daily. CONCLUSION: The distribution of the usual intake of iodine from brown seaweed in Koreans would be much tighter, resulting in a lower proportion of people exceeding the tolerable upper intake levels and possibly a lower mean intake than this study presented. Further study evaluating the iodine nutriture of Koreans based on the usual intake is warranted. Nevertheless, this study adds to the few reports on the iodine nutriture of Koreans.

• Journal of Nutrition and Health
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• 제44권1호
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• pp.82-91
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• 2011

The present study reviewed the effects of excess iodine intake on thyroid function and the incidence of thyroid disease and discussed the scientific basis for establishing a tolerable upper intake level (UL) of iodine for Koreans. ULs are defined as "the highest level of daily nutrient intake that is likely to pose no risk of adverse effects to almost all individuals in the general population." Koreans consume excess iodine from seaweed, and iodine intake is strongly influenced by seaweed consumption. However, no dose-response data derived from subjects consuming excess iodine frequently but not continuously during a lifetime are available. Therefore, the Korean DRI committee set the iodine UL to reduce the risk of adverse health effects by excess iodine intake for Koreans with distinctive seaweed-eating habits.

• Journal of Nutrition and Health
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• 제55권2호
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• pp.250-262
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• 2022

Purpose: Elevated iodine intake is related to a higher prevalence of subclinical hypothyroidism (SCH). We investigated the short-term effect of dietary iodine restriction on thyroid function in patients with SCH with high iodine intakes. Methods: The iodine levels in 64 SCH patients with serum TSH levels from 4.0 to 10.0 mIU/L and normal serum fT4 levels (n = 64) were assessed using 24-hour urine iodine test results and iodine intake levels calculated using a semi-quantitative food frequency questionnaire. Dietary iodine restriction was not recommended for patients with an iodine intake in the normal range (group A, n = 13), but seaweed restriction was recommended for patients with high iodine intakes (group B, n = 33). Thyroid functions and iodine levels were rechecked after three months. Another eighteen patients were prescribed thyroid hormone replacement therapy according to clinical criteria. Results: Median baseline iodine intake for the 64 patients was 290.61 ㎍/day, and median 24-hour urine iodine was 33.65 µmol/g of creatinine. The major source of dietary iodine was seaweed, which accounted for 72.2% of median baseline intake. Urine iodine and calculated iodine intake levels were positively correlated with serum TSH levels (p < 0.001 and p = 0.027, respectively), and calculated iodine intakes were significantly correlated with urine iodine levels (p = 0.001). In group B, iodine restriction significantly decreased urine iodine (p = 0.042) and TSH levels (p = 0.004), and conversion to euthyroid status was achieved in 16 of the 33 patients (48.5%). Conclusion: Iodine intake and urine iodine levels are correlated with thyroid function in SCH patients, and dietary iodine restriction can aid functional thyroid recovery in patients with elevated iodine intakes.

• 대한지역사회영양학회지
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• 제27권6호
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• pp.503-514
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• 2022

Objectives: This study examines the status of iodine intake and compares the characteristics (region and thyroid disease prevalence) according to the iodine-sourced food intake pattern in Chinese adults. Methods: An online survey was conducted by enrolling 437 Chinese adults aged 18-65 years, living in three regions with different iodine nutritional statuses: Sichuan, Chongqing, and Guangdong. Results: The prevalence of thyroid diseases in Sichuan, Chongqing, and Guangdong were 12.5%, 8.5%, and 2.8%, respectively. Conversely, the proportion of people who received thyroid disease-related examinations was a mere 37.5%. Among the subjects who underwent thyroid examination, the prevalence of thyroid disease in the three regions was 32.2%, 21.8%, and 8.0%, respectively. No differences were obtained in the total iodine intake by region, but the type of iodine source foods differed. Regardless of the region, the highest iodine content was obtained from seaweed. However, the iodine content from iodized salt and other foods differed significantly by region. Factor analysis revealed three food intake patterns according to the iodine food source. The study further determined regional differences and differences in the prevalence of thyroid disease according to food intake patterns. Conclusions: High salt intake can also increase iodine intake, which is thought to have an effect on the occurrence of iodine-excess thyroid disease. Hence, efforts focused on improving salty eating habits need to be implemented.

• Journal of Nutrition and Health
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• 제45권3호
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• pp.218-228
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• 2012

The prevalence rate of thyroid dysfunction (hypothyroidism and hyperthyroidism) has increased within the Korean population and seems to be affected by iodine dietary habits. Some studies reported that the prevalence of thyroid dysfunction increase both in the area of iodine deficiency and excess. In this study, we tried to discover the difference in iodine intake, anthropometric measurements, and blood parameters between male subjects with or without subclinical thyroid dysfunction. A total of 5,249 subjects (Euthyroid: 4706, SubHypo: 454, SubHyper: 89) were used in this study. There were no significant differences in BMI, body fat, visceral fat, waist circumference, SBP, DBP, total cholesterol, HDL-cholesterol, LDL-cholesterol, TG, fasting serum glucose, HbA1c, alcohol intake, however significant differences were noticed in both age and smoking status. Through a food frequency questionnaire (FFQ), iodine intake per day was estimated. The average iodine intake was similar (SubHypo $392.9{\pm}279.0{\mu}g$, Euthyroid $376.5{\pm}281.7{\mu}g$, SubHyper $357.3{\pm}253.8 {\mu}g$) among groups. The main source of iodine intake was eggs (52.8%, 54.2%, 52.4%) followed by milk (16.3%, 15.8%, 17.8%), then sea mustard & sea tangle (12.4%, 11.9%, 11.6%). The prevalence of subclinical hypothyroidism and subclinical hyperthyroidism was higher in subjects whose intake was higher than the recommended nutrient intake (RNI). These results suggest that the excess consumption of iodine intake may act as one of the risk factors regarding thyroid dysfunction in Korea. Therefore, an adequate amount of iodine intake is necessary in order to prevent subclinical thyroid dysfunction and clinical thyroid dysfunction.

• Journal of Nutrition and Health
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• 제30권10호
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• pp.1195-1202
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• 1997

Iodine-rich seaweed soup has been traditionally supplied to postpartum women in Korea. This dietary habit might introduce over-intake of iodine above the recommended requirements, and might provoke postpartum thyroid dysfunction. Although the response to excess iodine intake is highly variable, goiter, hyperthyroidism, hypothyroidism, and thyroiditis could follow the daily intake of 1,500$\mu\textrm{g}$ of iodine. A few studies are available concerning iodine toxicity in Korea. The purpose of this study was to investigate the relationships between the dietary intake of iodine and thyroid function change as well as the incidence of postpartum thyroiditis. One hundred and thirty-seven postpartum women who had experienced normal deliveries were studied. Dietary intake of iodine and excretion concentration of iodine in breast milk and maternal urine were measured . Serum T$_3$, T$_4$, TSH, anti-thyroglobulin antibody, and anti-microsomal antibody were anlayzed 1 week before delivery and 1, 6, 12, and24 weeks after delivery. Iodine intake was analyzed by one-to-one interviews using 24-hr recall and a food frequncy questionnaire. The result showed that the intake of dietary iodine before delivery and 1 and24 weeks after delivery were 483$\mu\textrm{g}$/day, 3367$\mu\textrm{g}$/day, and 1069$\mu\textrm{g}$/day, respectively. The concentration of iodine in urine at the first week after delivery was 63$\mu\textrm{g}$/dL, and 23.9$\mu\textrm{g}$/dL in breast milk . The levels of serum T$_3$ and T$_4$ before delivery were 2.01ng/mL and 11.49$\mu\textrm{g}$U/dL, respectively, showing that the levels were gradually dropping to normal values after delivery. Positive serum anti-thyroglobulin antibody and anti-microsomal antibody appeared in 3 cases. After a 24 week follow-up period , 6 women(10.3%) experienced cases of postpartum thyroiditis, 5 of which were cases of hyperthyroidism and one of which was a case of hypothyroidism. These figures of postpartum thyroiditis are similar to those of other countries.

• 대한지역사회영양학회지
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• 제26권1호
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• pp.48-55
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• 2021

Objectives: This study was conducted to estimate the dietary iodine intake of Koreans by a Total Diet Study (TDS) which provides 'closer-to-real' estimates of exposure to hazardous materials and nutrients through an analysis of table-ready (cooked) samples of foods. Methods: Dietary intake data from 2013-2017 Korea National Health and Nutrition Examination Survey (KNHANES) was used to select representative foods (RFs) for iodine analysis. A total of 115 RFs were selected and 158 'RF × cooking method-combination' pairs were derived by pairing each RF to corresponding cooking method(s) used more frequently. RFs were collected from 9 mega-markets in 9 metropolitan cities nationwide and mixed into composites prior to cooking preparation to a 'table ready' state for iodine analysis by inductively coupled plasma mass spectrometry. Iodine intake of Koreans was estimated based on the food intake data of the 2016-2018 KNHANES. Results: High iodine content was detected in seaweeds such as sea mustard and kelp. The mean iodine intake/capita/day was 418.4 ㎍ and the median value was 129.0 ㎍. Seaweeds contributed to 77.4% of the total iodine intake and the contribution by food item was as follows: sea mustard (44.0%), kelp (20.4%), laver (13.1%), milk (3.9%), egg (3.5%). Compared to the Dietary Reference Intakes for Koreans 2020, the proportion of people with iodine intake exceeding the tolerable upper intake level or below the estimated average requirement was high in the physiologically vulnerable groups (infants, children, pregnant women, and lactating women). Conclusions: The results, drawn from a TDS, are regarded closer to real estimates for iodine intake of Koreans compared with values in existing literature, which were based on a very limited variety of foods. On the other hand, it seems necessary to seek out solutions for the problematic iodine intake among physiologically vulnerable groups through in-depth analyses on food intake data collected with significant scale & quality.

• Journal of Nutrition and Health
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• 제27권10호
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• pp.1037-1047
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• 1994

Dietary iodine intake and urinary iodide excretion were meassured from 110 patients with various thyroid hormone diseses(hypothyroidism, hyperthyroidism, simple goiter and thyroid adenoma) and 67 normal control subjects. Iodine intake was assessed on the 24-hour recall dietary data using the compiled lists of food iodine values developed from various countries. Urinary iodide concentrations of drink water samples were measured with the iodide-selective electrode. The average iodine intake of the thyroid patients was 411$\mu\textrm{g}$, which was 87% higher(p<0.05) than that of the control subjects(220$\mu\textrm{g}$). Patients with hyperthyroidism and hypothyroidism or simple goiter excreted the most(0.6442ppm) amount of iodide respectively in the urine, with the control subject in the middle(0.5229ppm). Iodide concentrations of the drinking water samples were found to be in the range of 0.0015ppm to 0.0214ppm, which seemed to vary depending on the kind(underground water vs public water) and the location.

• Nutrition Research and Practice
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• 제10권2호
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• pp.167-174
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• 2016

BACKGROUND/OBJECTIVES: Despite the importance of a low-iodine diet (LID) for thyroid cancer patients preparing for radioactive iodine (RAI) therapy, few studies have evaluated dietary intake during LID. This study evaluated the amount of dietary iodine intake and its major food sources during a typical diet and during LID periods for thyroid cancer patients preparing for RAI therapy, and examined how the type of nutrition education of LID affects iodine intake. SUBJECTS/METHODS: A total of 92 differentiated thyroid cancer patients with total thyroidectomy were enrolled from Seoul National University Hospital. All subjects completed three days of dietary records during usual and low-iodine diets before $^{131}I$ administration. RESULTS: The median iodine intake was $290{\mu}g/day$ on the usual diet and $63.2{\mu}g/day$ on the LID. The major food groups during the usual diet were seaweed, salted vegetables, fish, milk, and dairy products and the consumption of these foods decreased significantly during LID. The mean energy intake on the LID was 1,325 kcal, which was 446 kcal lower than on the usual diet (1,771 kcal). By avoiding iodine, the intake of most other nutrients, including sodium, was significantly reduced during LID (P < 0.005). Regarding nutritional education, intensive education was more effective than a simple education at reducing iodine intake. CONCLUSION: Iodine intake for thyroid cancer patients was significantly reduced during LID and was within the recommended amount. However, the intake of most other nutrients and calories was also reduced. Future studies are needed to develop a practical dietary protocol for a LID in Korean patients.

• Journal of Nutrition and Health
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• 제50권6호
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• pp.624-644
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• 2017

본 연구는 우리나라와 일본의 식품성분표를 함께 이용하여 한국인 상용식품의 요오드 데이터베이스를 구축하였고, 1998년~ 2014년의 국민건강영양조사 자료를 이용하여 한국 성인의 요오드 섭취량 및 추이를 분석하였다. 조사대상자는 19세 이상 성인을 대상으로 하여 총 56,818명이며, 대상자의 일반적 사항, 식생활 관련 요인, 식품군, 식사제공 장소 등으로 나누어 요오드 섭취량을 분석하였다. 전체 요오드 섭취량은 1998년에서 2014년으로 갈수록 감소하는 추세를 나타냈다. 일반적 사항에서 남녀의 비율은 50% 내외로 비슷한 수준이었으며, 여성보다 남성의 요오드 섭취량이 높게 나타났다. 연령의 경우, 30 ~ 49세의 요오드 섭취비율이 39 ~ 46%로 가장 높았다. 식생활 관련 요인은 점심에 요오드 섭취비율이 1998년에서 2014년까지 29.4 ~ 34.4% 사이로 가장 높았다. 음식 제공장소 중 가정식에서 섭취하는 요오드 섭취량은 시간이 지남에 따라 감소하는 것으로 나타났다. 식품군에 따른 요오드 섭취량은 해조류가 가장 높게 나타났으며 음식제공 형태별 요오드 섭취량은 모든 연도에서 국 및 탕류가 가장 높은 것으로 조사되었다. 요오드 주요 급원 식품으로는 다시마가 가장 요오드 함유량이 많은 식품으로 조사되었고 그 외 카레소스를 제외하고 미역, 김 등의 해조류가 상위권을 차지하였다. 연구결과를 종합해보면 한국 성인의 요오드 섭취량은 적정 수준으로 나타났다. 하지만 요오드 섭취량의 경우에는 상한 섭취량 기준이 있는 미량 영양소인 만큼 섭취에 대한 지속적인 관심이 필요할 것으로 보인다. 또한, 요오드 섭취량 변화에 따른 갑상선 질환을 비롯한 다른 요오드 관련 질환이나 요인들과의 관련성을 살펴보기 위한 후속 연구들에 있어서 기초자료로 도움이 되길를 기대해본다.