How much seaweed for thyroid

Further, questions regarding types of products, macroalgae species, where the product was purchased, and how it was used as a part of the diet were included.

All questions regarding macroalgae in the diet were open ended except for given frequency intervals. In addition, the participants provided detailed information about macroalgae consumed on the same day as they took the urine samples.

There are no established portion sizes for edible macroalgae. Therefore, only participants who provided sufficient information about the quantity of macroalgae intake and the iodine concentration from the package labelling could be included for the estimation of iodine intake from macroalgae.

For three IH and five FFQ participants, the values were negative, as the estimated iodine intakes from food were probably overestimated. In those cases, the value zero was imputed into the dataset and used when calculating central and variation values of the variable.

Dependent variables were checked for normality using Q—Q plots and the Shapiro—Wilk test. Due to the skewed distribution and low number, non-parametric tests were used. Independent group differences were examined using the Mann—Whitney U test for comparison of two groups, and Kruskal—Wallis test was used for comparison of categories with more than two groups. Characteristics of the study participants are presented in Table 1. UIC measured 3—4 and 7—8 h after ingestion of macroalgae is presented in Table 2 , together with habitual and 24 h iodine intake.

FFQ: Food frequency questionnaire. As shown in Table 2 , the median UIC was similar between the first and the second sample. There was a significant correlation between UIC from the two time-points.

The participants reported the type of macroalgae consumed on the day of the urine sample. Of the 19 participants in the subgroup, one participant had a TSH value above the laboratory reference 4. Table 5 shows the frequency of habitual seaweed consumption last four weeks and procurement details. Products with macroalgae as an ingredient were used by 35 of the participants, and macroalgae as a supplement by five participants.

Most of the participants used products from more than one category. Sugar kelp Saccharina latissima , winged kelp Alaria esculenta , and dulse Palmaria palmata were the species that most participants reported to consume habitually in the category of whole macroalgae products. An overview of macroalgae species consumed habitually FFQ is reported in Table 6.

Multiple answers were allowed. This might be underestimating the frequency of use, as different products may have been sued at different days. Percentage is given within category, including missing. Several reasons for including macroalgae in the diet were given by the participants Table S2.

Sugar kelp, winged kelp, dulse and laver were the most used macroalgae species. Therefore, the risk of adverse health effects from excessive iodine intake in this study population can be considered high.

This is in line with an Irish study, examining iodine content of 19 commonly consumed macroalgae species, where the iodine content between species was highly variable [ 37 ]. For the species with the highest iodine content, sugar kelp, only 0. The median daily iodine intake from food alone was considerably lower than the UIC.

This indicates that macroalgae were the main contributor to dietary iodine in this study. Due to the design of the study and the lack of accurate data on the iodine content of the consumed macroalgae products, we cannot report on the bioavailability of iodine.

However, as the contribution of iodine from macroalgae was high, and by far exceeded the contribution from other foods, the absorbed amount of iodine is likely to be substantial. The difference in bioavailability between species has been suggested to be related to the share of iodine stored in inorganic and organic form, such as mono- and di-iodothyrosine MIT and DIT , in macroalgae, where humans absorb inorganic iodine, such as potassium iodine KI or iodate IO 3 - , more effectively than organically bound iodine, e.

However, factors such as iodine status and current thyroid function may also be of importance for iodine uptake in humans [ 36 ]. In this study, one participant had subclinical hypothyroidism, as indicated by a TSH above the reference value, and two had positive TPOAb with thyroid function tests within the laboratory references.

Compared with median TSH levels for men and women 1. Similarly, the mean serum TSH 2. In our study, we cannot say whether the TSH levels increased due to macroalgae ingestion because of the nature of the observational study design.

Thyroid function, however, might have been differently affected in the remaining group having an excessive iodine intake. Additionally, the time of the blood samples were not standardized according to macroalgae intake, thus, a transient rise in TSH may have occurred unnoticed.

Further studies are required to examine thyroid function in macroalgae consumers with an excessive iodine intake. Previously, several case studies have reported iodine-induced thyroid dysfunction in adults consuming seaweed [ 42 , 43 , 44 , 45 ]. Thyroid dysfunction has also been seen in new-born babies after excessive maternal iodine intake from macroalgae [ 46 , 47 ]. A Japanese study reported elevated TSH after ingestion of high iodine from Kombu [ 22 ], and the authors advised against consuming excessive amounts of seaweed.

Three population studies found an increase in UIC and TSH after macroalgae supplementation in euthyroid adults [ 8 , 27 , 48 ]. In all three studies, UIC and hormone levels returned to baseline after cessation of macroalgae supplementation.

These studies were of short duration and do not reflect the effect that excessive iodine may have on the thyroid gland after years of macroalgae consumption. The prevalence of subclinical hypothyroidism in young children from the same population was 9. In a systematic review and meta-analysis, the risk of subclinical hypothyroidism was significantly higher among men and women with iodine excess than among those with adequate iodine intakes [ 52 ].

Furthermore, the systematic review showed a dose-related increase in the prevalence of subclinical hypothyroidism as the level of UIC increased.

Hence, macroalgae with a high concentration of iodine should be used with caution, especially in vulnerable groups such as pregnant women, as the fetus is susceptible for high maternal iodine intake and maternal thyroid function [ 53 , 54 ].

Further, as a large cohort study found that even mildly elevated TSH preconception could result in negative pregnancy outcomes, women in fertile age should also use high-iodine macroalgae with care [ 55 ]. Other known vulnerable groups to iodine excess are people with thyroid disease or thyroid autoimmunity [ 56 ]. Sugar kelp Saccharina latissima was the most popular species in our study. After sugar kelp, winged kelp Alaria esculenta and dulse Palmaria palmata were the species that most participants mentioned in the dietary survey in the category of whole macroalgae products.

A large share of the products the participants reported to consume were not labeled with iodine concentration. Due to variations in iodine concentration with season, harvesting location, age, and size of the macroalgae, storage and processing conditions, the iodine concentration is difficult to determine without specific analysis of products. The iodine concentration for the same species may vary considerably [ 5 ]. With such variations in iodine content and with products without iodine declaration, it is difficult to decide if a product is safe to consume.

This is the first study to examine iodine status and thyroid function among macroalgae consumers in Norway, thereby providing new insights into an area of limited research. The urine samples in this study were collected with a predetermined time-interval 3—4 h and 7—8 h after consumption of macroalgae. These time intervals were chosen based on the investigation of urinary iodine excretion in humans after consumption of Ascophyllum nodosum , [ 27 ].

It is considered a strength that we have two urine samples per participant, however, it must be noted that UIC from this study provides information about the iodine status after macroalgae consumption.

If macroalgae are consumed only once a week, the total iodine intake per week may remain low, and the UIC is only representative for a day with consumption of macroalgae. During the participant recruitment, there were 24 passive dropouts, meaning that they reported interest in the study and received a consent form and the necessary supplies to participate, but never followed up further.

We do not know whether these individuals were different from the study population. Additionally, the sample size was small, and we cannot exclude the possibility of selection bias. The subsample providing information about thyroid function was small and not representative of the whole study population, as the median UIC differed significantly from the group that only provided urine samples.

Conclusions about thyroid function for the whole study sample can therefore not be drawn. Most participants were recruited from specific areas where harvested macroalgae were used as whole food. Due to limited time, participants using commercially available macroalgae products were probably underrepresented, as recruitment in health food stores, global food stores or chain stores was time-consuming. Macroalgae may also be a source of contaminants, such as heavy metals and especially inorganic arsenic [ 58 ].

The potential exposure risk of these, and other undesirable components from macroalgae, was not evaluated in this study and requires further investigation. Wholefood macroalgae was the most consumed macroalgae product, and sugar kelp, winged kelp, dulse and laver were the most common species. Iodine status in macroalgae consumers is excessive after intake of macroalgae. However, for many products, iodine declaration was lacking.

Macroalgae with low-level iodine used in appropriate amounts may be a good dietary source of iodine. Still, precaution must be taken before consuming macroalgae as it may give a high iodine exposure. Population groups vulnerable to high iodine intakes should avoid consuming macroalgae in order to reduce the risk of negative health consequences of excessive iodine intakes. The recommended daily intake of iodine for adults is micrograms 20,th of a teaspoon.

The thyroid, a small butterfly-shaped gland in the lower part of the neck, needs iodine to produce essential hormones that regulate the metabolism. But excessive amounts of iodine can lead to hyperthyroidism overactive thyroid causing symptoms including palpitations, fatigue and weight loss while low levels can cause hypothyroidism underactive thyroid causing fatigue, weight gain and confusion.

Thyroid Australia estimates about , Australians suffer from thyroid dysfunction, with more than 40, new cases developing each year. The Federal Department of Health and Ageing, alarmed by the increasing number of people with thyroid conditions linked to seaweed, issued a warning to doctors, endocrinologists and state and territory chief health officers last year.

DHS spokesman Graeme Walker said that since October, dried brown seaweed with iodine levels above milligrams per kilogram had been banned for importation into Australia following the Bonsoy case. Its iodine concentration can vary greatly, which poses a risk for a developing fetus 36, MacArtain P, et al.

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Among the foods to go easy on are soy, kelp and dietary supplements like iodine and selenium, says endocrinologist Christian Nasr, MD. Soy: If you have hypothyroidism, yes. Eating too much soy causes problems only for those with hypothyroidism , which occurs when your thyroid gland does not make enough thyroid hormones, Dr.

Nasr says. The main problem is that soy may hinder absorption of the hormones that such patients take. Turnips and root vegetables: No. They are good for your diet, regardless of any thyroid issues.