Adequacy of iodine intake in three different Japanese adult dietary patterns: a nationwide study

Background: Iodine intake is considered to be high in Japan due to regular seaweed consumption. Subgroups that do not have a traditional Japanese-style diet may consume insufficient amounts of iodine. Method: Three hundred and ninety apparently healthy adults (195 men and 195 women) aged 20 to 69 years from 20 areas throughout Japan completed four-day diet records and collected a 24-h urine sample. Dietary patterns were extracted from 31 food groups by cluster analysis. The iodine adequacy of each dietary pattern was examined using reference values from the Dietary Reference Intakes for Japanese. Results: Three dietary patterns, labelled Cluster I (Rice and vegetables) (n = 101), Cluster II (Meat, non-Japanese noodles, and sugar-sweetened beverages) (n = 34), and Cluster III (Fish, Japanese noodles, and alcohol) (n = 60), were identified in male subjects. Another set of three patterns, Cluster I (Rice and vegetables) (n = 22), Cluster II (Fish and Japanese noodles) (n = 33), and Cluster III (Bread and non-Japanese noodles) (n = 140), was found in female subjects. Although the habitual iodine intake of almost all participants was above the estimated average requirement (EAR), iodine intake was statistically significantly lowest in Cluster II in men and Cluster III in women. Moreover, the mean participant age was the youngest in these clusters. Conclusion: Although Japan is known as a high iodine-consuming country, some Japanese individuals who do not eat a traditional Japanese-style diet consume low amounts of iodine. Since younger people tend to have modern, Westernized dietary patterns, iodine deficiency might be given additional consideration hereafter in Japan.