Commercially available kelp and seaweed products – valuable iodine source or risk of excess intake?

Background: Seaweeds and kelps, also known as macroalgae, have long been common in the East-Asian diet. During recent years, macroalgae have entered the global food market, and a variety of macroalgae products are now available for consumers. Some macroalgae species are known to be particularly rich in iodine, but little data regarding the iodine content of macroalgae-containing foods exists. Objective: The aim of this research study was to analyse the iodine content in a large variety of commercially available macroalgae-containing foods and supplements and to evaluate whether such products are sources of adequate dietary iodine. Design: Ninety-six different products were collected after surveying the Norwegian market for commercially available macroalgae products, collected from three categories: 1) wholefood macroalgae products (n = 43), 2) macroalgae-containing foods (n = 39), and 3) dietary supplements containing macroalgae (n = 14). All products were analysed for iodine content by inductively coupled plasma-mass spectrometry (ICP-MS). Results: The iodine content in one portion of wholefood macroalgae products ranged from 128 to 62,400 μg. In macroalgae-containing foods, the iodine content ranged from 30 to 25,300 μg per portion, and in supplements it ranged from 5 to 5,600 μg per daily dose. The species with the highest analysed iodine content were oarweed, sugarkelp and kombu, with mean iodine levels of 7,800, 4,469 and 2,276 μg/g, respectively. For 54 products, the intake of one portion or dose would exceed the tolerable upper intake level (UL) for iodine. Discussion and conclusion: The iodine content in the included products was variable and for most products high, exceeding the tolerable upper intake level (UL) if consumed as a serving or portion size. The labelling of macroalgae species included, and declaration of iodine content, were inadequate or inaccurate for several products. As macroalgae-containing products are unreliable iodine sources, inclusion of such products in the diet may pose a risk of consuming excessive amounts of iodine.