Due to variation of iodine content from one seaweed species to the next, along with confusion stemming from wet and dry weight terminology, many inaccurate assumptions have been made regarding the amount of iodine the Japanese actually consume from seaweed. Not all studies, dietary records or surveys specify whether daily or yearly consumption of seaweeds is recorded using wet weight, dry weight or a combination of the two. In some reports seaweed consumption has been estimated at 4-7 g/day dried weight [17
], while other reports claim consumption of 12 g/day using both wet and dry weight
]. Certain seaweeds have a swelling capacity of nearly ten times their dry volume with moisture content typically over 70% when wet and around 7-20% when dried [33
]. The difference between wet and dry weight, along with the type of seaweeds being consumed, can result in extreme overestimation (more likely) or underestimation (less likely) of Japanese iodine intake.
Interpreting information to determine Japanese seaweed consumption and resulting iodine intake is a difficult task, and with ever changing diets, a close estimate is all that can be made. Nori and wakame are the most commonly consumed seaweeds in Japan, with nori accounting for 45% and wakame accounting for 30% (75% together) of total seaweed consumption, as stated by the Food and Agriculture Organization of the United Nations [35
]. Based on previous estimates and records, dried seaweed consumption of 4-7 g/day [17
] results in iodine intakes between 79 and 139 μg/day from nori and wakame when calculated using dried iodine contents of 16 and 42 μg/g respectively [18
]. The remainder of iodine intake is derived mainly from kombu consumption, with smaller amounts coming from other seaweeds that have nominal iodine content.
Kombu has the highest iodine content of all seaweeds in the Japanese diet. In 2006 consumption of kombu/household/year was 450 g [19
], and with an average of 2.55 members per household in Japan in 2005 [36
], 0.48 g kombu/person/day was consumed. When calculated, 0.48 g of kombu with an iodine content of 2,353 μg/g [18
] equates to 1,129 μg/day of iodine. Assuming negligible iodine intake from the other seaweeds consumed, daily iodine intake from nori, wakame, and kelp can be estimated at 1,208 to 1,268 μg/day (1.2 to 1.3 mg/day). It is reasonable to assume that iodine intake per day based on seaweed consumption frequency and iodine content averages around 1,000-2,000 μg/day (1-2 mg/day).