Thyroid Res. 2011; 4: 14.
Published online 2011 October 5. doi: 10.1186/1756-6614-4-14
Assessment of Japanese iodine intake based on seaweed consumption in Japan: A literature-based analysis
Theodore T Zava1 and David T Zavacorresponding author1
Japanese iodine intake from edible seaweeds is amongst the highest in the world. Predicting the type and amount of seaweed the Japanese consume is difficult due to day-to-day meal variation and dietary differences between generations and regions. In addition, iodine content varies considerably between seaweed species, with cooking and/or processing having an influence on iodine content. Due to all these factors, researchers frequently overestimate, or underestimate, Japanese iodine intake from seaweeds, which results in misleading and potentially dangerous diet and supplementation recommendations for people aiming to achieve the same health benefits seen by the Japanese. By combining information from dietary records, food surveys, urine iodine analysis (both spot and 24-hour samples) and seaweed iodine content, we estimate that the Japanese iodine intake–largely from seaweeds–averages 1,000-3,000 μg/day (1-3 mg/day).
Japanese iodine intake exceeds that of most other countries, primarily due to substantial seaweed consumption. Iodine is an essential element required for thyroid hormone synthesis, believed to impart some of its antioxidant and antiproliferative activity in the prevention of cardiovascular disease and cancer [1-8]. Seaweeds have the unique ability to concentrate iodine from the ocean, with certain types of brown seaweed accumulating over 30,000 times the iodine concentration of seawater . The amount of iodine the Japanese consume daily from seaweeds has previously been estimated as high as 13.5 to 45 mg/day by sources that use ambiguous data to approximate intake [10,11], an amount 4.5 to 15 times greater than the safe upper limit of 3 mg/day set by the Ministry of Health, Labor and Welfare in Japan . While high iodine intake from seaweed consumption is believed to have numerous health benefits, it has been reported to negatively affect individuals with underlying thyroid disorders [13-16]. To prevent excessive consumption it is imperative for people seeking health benefits from a high iodine diet to be knowledgeable of the amount of iodine the Japanese consume daily. In this paper we use a combination of dietary records, food surveys, urine iodine analysis, and seaweed iodine content to provide a reliable estimate of Japanese iodine intake, primarily from seaweeds.