To improve the efficacy of radioactive
iodine (RAI)
therapy for differentiated
thyroid cancer patients, a low-
iodine diet (LID) prior to the
therapy is recommended. In
iodine-rich areas such as Korea, however, a strict LID is very difficult to maintain. We experienced the cases of three patients showing low adherence to the LID before initial RAI
therapy, and analyzed the main food source supplying
iodine during the LID, and examined the influence of the poorly maintained LID on the efficacy of RAI
therapy. The dietary intake during the LID periods were assessed using three-day dietary records and remnant thyroid activity after the second RAI administration was also evaluated. All patients' mean daily
iodine intake during two-week LID periods exceeded the 100 µg guideline set by the Korean Thyroid Association (median 110.9 µg, ranges 100.4-117.0 µg). Although the typical food sources of
iodine intake are seaweeds in Korea, salted vegetables were the main contributor to the patients'
iodine intake during the LID periods. Remnant thyroid activity was shown on a follow-up scan in all of 3 patients suggesting low efficacy of RAI
therapy. In summary, the patients with low adherence to the LID guideline showed unsuccessful remnant ablation, and the main food source of
iodine was salted vegetables. Further studies are necessary to examine the relationship between adherence of the LID and RAI efficacy according to dietary
iodine intake levels, as well as food sources that cause low adherence to the LID. These data can then be used to develop more practical LID guidelines.