Iodine from brown algae in human nutrition, with an emphasis on bioaccessibility, bioavailability, chemistry, and effects of processing: A systematic review

Abstract

Brown algae are becoming increasingly popular as a food source and dietary supplement in Europe and other Western countries. As they are highly rich in iodine, they represent a potential new dietary iodine source. Iodine deficiency has been re‐emerging in Europe, and it is important to ensure adequate intake through one's diet. However, macroalgae, and especially brown algae, may contain very high amounts of iodine, and both iodine deficiency and excessive iodine may increase the risk of negative health effects. The iodine content of algae or foods containing algae is currently not regulated in the European Union. The aim of this paper is to review the literature to determine the chemical species of iodine in brown algae, the loss of iodine during processing, and the bioavailability and bioaccessibility of iodine. A systematic search of the literature was performed in April 2021, via the databases Web of Science and PubMed. The review includes studies of iodine in brown macroalgae in relation to bioavailability, bioaccessibility, processing and speciation. A meta‐analysis was conducted in relation to the following topics: (i) the correlation between total iodine and iodide (I–) content in brown algae; (ii) the correlation between the loss of iodine during processing and the I– content; and (iii) the correlation between bioavailability and the I– content. The bioavailability of iodine from brown algae was generally high, with in vivo bioavailability ranging from 31% to 90%. The in vitro bioavailability of iodine (2%–28%) was systematically lower than in vivo bioavailability (31%–90%), indicating an inadequate in vitro methodology. Processing may reduce the iodine content of brown algae, and a higher I– content was positively correlated with increased iodine loss during processing. Although processing strategies may reduce the iodine content of brown algae significantly, the iodine content may still be high after processing. These findings may be used in food safety evaluations of brown algae as well as in the development of macroalgae‐containing foods with iodine contents suitable for human consumption. Further research on processing techniques to reduce the iodine content in brown macroalgae are warranted.

A Nordic approach to food safety risk management of seaweed for use as food

“…The great variability in the content of heavy metals and iodine within each species, and several in luencing factors on food quality, are described by several other authors (Banach et al, 2020;Blikra et al, 2022, Steinhagen et al, 2022.…”

“…A Norwegian report (Duinker et al ., 2020) indicates a bioavailability of 73-78% of iodine from sugar kelp, found in a rat model study. A review article states that the bioavailability of iodine from brown algae is generally high, with in vivo bioavailability ranging from 31 to 90% (Blikra et al, 2022).…”

Iodine Bioavailability and Accumulation of Arsenic and Cadmium in Rats Fed Sugar Kelp (Saccharina latissima)

“…However, iodine bioavailability in different types of seaweed varies, and overall bioavailability estimates are significantly influenced by the iodine status of the study population [ 14 ]. A recent systematic review reported that the bioavailability of iodine from brown algae in vivo varied from 31% to 90% [ 25 ]. The bioavailability of iodine and iodine absorption from different seaweeds has been proposed to be affected by the polysaccharide matrix of the seaweed [ 15 ] and may delay iodine absorption compared with KI.…”

“…Another factor affecting bioavailability is the form of iodine in seaweed. Seaweed contains both organic and inorganic iodine [ 26 ], and most brown algae and algae with a high iodine content contain most of the iodine in the form of iodide [ 25 ]. The exact mechanisms underlying the lower iodine bioavailability in sugar kelp compared to KI found in this study were not investigated, but differences in matrix, fibre content, and excretion route could be possible explanations.…”

Iodine biofortification of bean (Phaseolus vulgaris L.) and pea (Pisum sativum L.) plants cultivated in three different soils

“…Both insufficient and excessive iodine intake can affect the synthesis of thyroid hormones. Higher iodine consumption (more than the maximum amount of 1100 μg/day; the maximum tolerable value of 600 μg/day set by the Scientific Committee on Food) leads to thyrotoxicosis and autoimmune thyroid problems, while iodine deficiency results in hypothyroidism, goitre, brain damage, and other diseases such as cretinism and stomach cancer [3][4][5][6]. Iodine deficiency disorders (IDDs) affect ca.…”