Consequences of acute and long-term excessive iodine intake: A literature review focusing on seaweed as a potential dietary iodine source

Macroalgae, also called seaweed, are becoming more widespread as food in Western diets. Seaweed can accumulate iodine, an essential nutrient for humans. However, some species of seaweed may contain very high amounts of iodine, and therefore, iodine has been identified as one of the major hazards in the seaweed food chain. Macroalgae may be consumed regularly, though many consumers report eating macroalgae only occasionally. The aim of this paper is to explore possible health consequences of excessive iodine intake according to long-term (chronic) or occasional (acute) excessive exposure to iodine, relating to a regular (chronic) or occasional (acute) seaweed intake, respectively. Furthermore, through a modeling exercise, we add different amounts of seaweed to the diet in a population group to explore the possible safe amounts that can be added without exceeding excessive iodine intakes and risking detrimental health effects. Chronic excessive iodine intakes were associated with several negative health outcomes at variable doses in various studies. For acute excessive iodine exposure, negative health effects seemed to be associated with higher iodine exposures. However, the research on this topic was limited. The chronic and acute iodine exposures needed to result in negative health outcomes may easily be ingested by macroalgae consumption. Adding seaweed to the diet must be done thoughtfully to avoid the risk of exceeding thresholds for excessive iodine intake.