Which kelp for iodine

Sushi was excluded from the market survey, as sushi and nori, which are the sheets that are typically used to wrap sushi rolls, had already been collected and analysed by the Norwegian Food Safety Authority NFSA In total, 96 products were collected, and an overview of the collected products is shown in different product categories Fig. The in-store survey was limited to the two largest cities in Norway, Oslo and Bergen. We aimed at selecting products that were available at a large scale if possible.

Three separate items, preferably with three separate batch numbers, of each identified product were purchased. If different batch numbers were not possible to obtain, we selected products with different best before dates BBDs.

If neither different batch numbers nor BBDs were available, three items were conveniently selected. The following information labelled on the product packaging was recorded: type of macroalgae common name , macroalgae species Latin name , compliance with language requirements for labelling of products, declared iodine content and the recommended dose for supplements.

For each product, equal quantities were drawn from the three collected items of the product to form a homogenised composite sample. A subsample of 20—50 g was taken from the composite sample, freeze-dried and re-homogenised before being portioned in appropriate amounts for analysis.

Thirty products displayed specific cooking instructions on the product packaging. These products were prepared accordingly with the purpose of comparing the iodine content before and after cooking. Of the 30 processed samples, 21 consisted of processed macroalgae, 6 consisted of processed macroalgae and broth, and three samples consisted of only broth.

Water samples were extracted from the boiling pot using a pipette after hydrothermal preparation of the macroalgae.

When multiple preparation suggestions were provided, rehydration was chosen. Where different heat treatments were suggested, boiling was preferred over baking in the oven. A detailed description of the different cooking methods is provided in Appendix 1. Samples were prepared by adding tetramethylammonium hydroxide, x03B1;-amylase and water to the freeze-dried sample.

Composite samples were analysed with one analytical replicate per sample. Individual samples of water were analysed. For the recollected products, individual samples of three replicates were studied. This was carried out by trained laboratory technicians. The limit of quantification LOQ for the method was calculated as 10 times the standard deviation SD from 20 blind samples analysed on the same day, and was estimated to be 0.

The analysed values of standard reference materials are shown in Table 1. All iodine values were calculated from freeze-dried samples back to the original sample and are, therefore, considered as wet weight w. RSD, relative standard deviation. For wholefood macroalgae products, a portion size of 8 g was applied as suggested by others 7. If standard portion sizes were not found, we used a unit or an otherwise suited measure.

All portion sizes used are described in Appendix 2. For one powdered supplement, the quantity was provided in teaspoons, and as there is no standard weight for different types of macroalgae powder, the dose recommended for a powder product by a different manufacturer was used. The recommended dosage and the calculations are described in Appendix 3. The type of store where the products were purchased and their country of origin is tabulated in Table 2.

A large share of the wholefood products 31 of 40 exceeded the UL for iodine, and some of the products by manyfold. Sugar kelp and oarweed were the two species with the highest iodine content and the UL would be exceeded 59 and times, respectively, by intake of one portion. However, consuming only one gram of the sugar kelp and mixed species flakes from the spice grinders would exceed the UL by 7.

Twenty-one out of the 39 macroalgae-containing foods would exceed the UL if consuming one portion size. For salt and seasoning blends, a daily intake of 6 g was used in the calculations.

The two food products with the highest iodine contribution from one portion included chocolate and breading. The contribution of the recommended daily dose of each macroalgae-containing supplement to the RI and UL is tabulated in Table 5. At the same time, the recommended dose for four products exceeded the RI, and two products would lead to an iodine intake exceeding the UL for iodine. Most of the supplements had a substantially lower iodine content than the content declared on the product packaging.

For the supplements with an iodine declaration, all analysed iodine values were lower than the declared content, except for one product. In the collected products, 17 different species of macroalgae were identified. The most commonly found species were sugar kelp Saccarina latissima , winged kelp Alaria esculenta and wakame Undaria pinnatifida , all from the group of brown algae.

Table 6 shows the iodine content within the different product categories according to the groups: brown, red, green and mixed algae. Within all the three product categories the products containing brown macroalgae reported the highest iodine content.

Different products were labelled according to the common name and species at a varying accuracy. For 12 products, neither the common name nor the Latin name of the species was included on the package insert.

For seven products, the species were identified through oral communication with the manufacturers, and for the remaining five products, the species included were unidentified. For three products, the common and Latin name did not match. Of the wholefood products, 21 declared the iodine content, whereas 22 did not. For the foods containing macroalgae, only three of 39 products declared the iodine content.

For these, the analysed values were lower than the declared Table 7. For the majority of the macroalgae products, the analysed values were markedly different from the declared values.

For 14 of the products, the analysed iodine content was lower than the declared content, while for 10 products, the analysed iodine content was higher than the declared content. The values of iodine content in unprocessed samples and in samples prepared according to the cooking instructions from the manufacturer are presented in Table 8.

For the samples where consumption of the broth was recommended, the iodine content in water was analysed as well. For most products, the iodine content was reduced on a dry weight basis after cooking. All single values are obtained from measurements in pooled samples comprising three sub-samples for each product. This research study presents analysed values of iodine content in a wide range of commercialised macroalgae food products and supplements.

We found a significant variation in the iodine content between the different products of macroalgae. Several products had inadequate labelling of species included and iodine content. Consumption of one portion 8 g 7 of the different wholefood macroalgae products would provide a higher intake of iodine than UL for 31 of 40 products.

The species included in the products which were not exceeding the UL were Irish moss Chondrus crispus , truffle seaweed, nori Porphyra spp. For the remaining species, as well as the mixed-species products, the UL would be exceeded by at least 1.

Macroalgae-containing foods with moderate-to-low iodine levels may be used as an alternative iodine source, for example, by those who exclude or limit lean fish or dairy from the diet, and one portion of a macroalgae-containing food could contribute substantially to the RI for iodine.

However, for most of the macroalgae-containing foods included in this study, one portion would exceed the RI and for several foods also the UL. Thus, frequent consumers of these products may be at risk of adverse health consequences caused by excessive iodine intakes.

A long-term excessive iodine intake has been associated with hypothyroidism, goitre, autoimmune thyroid disease and iodine-induced hyperthyroidism in epidemiological studies 37 , An excessive iodine intake has also been associated with adverse effects on foetal growth Thyroid disorders caused by an excessive iodine intake from dietary macroalgae have been described in different population groups, such as neonates 40 , breastfed infants 41 , school aged children 42 , and adults 43 , Still, the mechanisms of excessive iodine intake and its consequences on health remain an area of limited research, and further studies are warranted.

We found that kelps of the brown algae group represent the most concentrated sources of iodine, which has been confirmed by others 15 , 16 ; however, large variations were observed both within and between species in the wholefood macroalgae products.

A US study from analysed a large amount of commercially available seaweeds, including 12 different species Possible reasons for high intra-species variability may be due to different life stages of the thallus or different parts of the thallus included in the different analysed samples However, as these samples were store-bought and ready to consume, post-harvest storage conditions may have affected the iodine content, as iodine may be reduced with time when stored in open containers, particularly under humid conditions Variations in iodine content are also found in conventional foods, such as lean fish, processed fish i.

The declared iodine content per recommended dose deviated with more than the measurement uncertainty for most supplements, indicating that the declared values are not reliable. Based on the highly variable iodine content in macroalgae-containing supplements, such supplements may pose a health risk. Others have advised against the use of macroalgae-containing dietary supplements, and a review of iodine supplement use in pregnancy recommended that women who are pregnant, lactating or planning to conceive should refrain from using such supplements The labelling of the macroalgae products included in this study was variable, and for 12 products, the product packaging did not provide any information regarding the type of macroalgae.

In the current legislation, labelling of vitamins and minerals for food products is not mandatory, and the passing of such information is voluntary for manufacturers. In Norway, the NFSA has recommended the manufacturers of the macroalgae industry to label the macroalgae products with details regarding iodine content With such variable labelling, often lacking either iodine content, species or both, it is impossible for the consumer to evaluate the iodine content and food safety of the products.

Processing of the macroalgae products, such as blanching and boiling, has reduced the iodine content in seaweeds and kelp 51 , During processing, macroalgae absorb water, which is species dependant 53 ; however, a higher water content in the product will result in a dilution effect of the iodine concentration when given on a wet weight basis. Much of the apparent reduction in iodine content on a wet weight basis that we found is thus a result of a higher water content after processing, and hence, calculating iodine loss or retention should be performed on a dry weight basis Of the 43 wholefood macroalgae products included in this study, 30 had preparation instructions, presented either as serving suggestions or as methods proposed in order to reduce the iodine content.

Moser M, Buchberger W, Mayer H: Influence of an iodine-drinking cure on the antioxidative status of diabetes patients. Wien Klin Wochenschr , — CAS Google Scholar. Adv Clin Path , 4: 11— Planta , — Gaby's editorial on iodine. The Original Internist , — Miller D: Iodine for health. Daiichi Shuppan Publishing. Tokyo; — Thyroid , — Arasaki S, Arasaki T: Vegetables from the sea. Tokyo: Japan Publications Inc; Nagataki S: The average of dietary iodine intake due to the ingestion of seaweeds is 1.

Nutr Rev , 31— Naylor J: Production, trade and utilization of seaweeds and seaweed products. Matsumura Y: Nutrition trends in Japan. J Nutr Sci Vitaminol , — Yoshinaga J, Morita M, Yukawa M, Shiraishi K, Kawamura H: Certified reference material for analytical quality assurance of minor and trace elements in food and related matrixes based on a typical Japanese diet: interlaboratory study. J Epidemiol , SS Sci Total Environ , — Nippon Naibunpi Gakkai Zasshi , 91— Toyokawa H: Nutritional status in Japan from the view-point of numerical ecology.

Soc Sci Med , — Matsuzaki S, Iwamura K: Application of seaweeds to human nutrition and medicine. In In Nahrung aus dem Meer; Food from the sea. New York: Springer; — Asia Pac J Clin Nutr , — J Nutr , — Jpn Agr Res Q , — Rajadurai MR: Production, marketing and trade of seaweeds. Hays MT: Estimation of total body iodine content in normal young men. In In Williams textbook of endocrinology. Philadelphia: W. Saunders Company; — Nagataki S, Shizume K, Nakao K: Thyroid function in chronic excess iodide ingestion: comparison of thyroidal absolute iodine uptake and degradation of thyroxine in euthyroid Japanese subjects.

Mettlin C: Global breast cancer mortality statistics. CA Cancer J Clin , — Br J Cancer , — Circulation , ee With chartbook on trends in the health of Americans.

Hyattsville, MD; Endocr J , — Acta Endocrinol Copenh , — Clin Endocrinol Oxf , — Endocrinology , — Having an excessive amount of iodine can disrupt the normal function of the thyroid and should be avoided.

It is important not to have too little or too much iodine. Maintaining a balanced diet should adequately cover the daily requirement, however, those on restricted diets should look in to taking iodine in a supplement form. Contact our Nutrition Advice Team by clicking here. Shrimp and other seafood are good sources of iodine because they absorb some of the iodine that is naturally present in seawater Tuna is also a low-calorie, high-protein, iodine-rich food.

Furthermore, it is a good source of potassium, iron and B vitamins Tuna is also a good source of omega-3 fatty acids , which may lower your risk of heart disease Fish higher in fat offer lower amounts of iodine.

Since tuna is a fattier fish, the amount of iodine found in tuna is lower than leaner fish varieties, such as cod For fewer than calories, one whole egg provides a lean source of protein, healthy fats and a wide assortment of vitamins and minerals However, the majority of these nutrients, including iodine, come from the yolk Egg yolks are a good source of iodine because it is added to chicken feed.

Yet since the content of iodine in chicken feed can vary, the amount found in eggs can also fluctuate 12 , Prunes are a good vegetarian or vegan source of iodine. Prunes are commonly known for helping relieve constipation. This is because of their high content of fiber and sorbitol, a type of sugar alcohol Prunes are high in many vitamins and nutrients, including vitamin K, vitamin A, potassium and iron Because of the nutrients prunes offer, they may help improve heart health, decrease the risk of colon cancer and even help manage weight by decreasing appetite 25 , 26 , Lima beans are commonly associated with the popular Native American dish succotash, which mixes lima beans and corn.

Lima beans are a good source of fiber, magnesium and folate, making them a heart-healthy choice Due to the variation of iodine in soil, irrigation water and fertilizers, the amount of iodine can vary in fruits and vegetables 6 , This is why many people around the world are at risk of developing a deficiency. The foods highest in iodine include seaweed, dairy, tuna, shrimp and eggs. Additionally, most table salt has been iodized, providing an easy way to add iodine to your meals.

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