The Iodine Bioavailability and Its Metabolic Response for Kombu and Potassium Iodide Intake in Chinese Adults

The consumption of kombu plays an important role in the traditional dietary habits of East-Asian countries. However, data on the metabolic profile of kombu-derived iodine remain limited. Totally, 20 Chinese participants (age 19.6 ± 2.7 years) were recruited and allocated to two parallel intervention groups. One consisted of a meal with kombu supplement (providing 993 and 1735 μg iodine), and the other of potassium iodide (KI, containing 547 and 1263 μg iodine) at the two interventions. The iodine bioavailability was assessed based on the 0-24 h urine samples, and the metabolic response was characterized by urinary iodine excretion velocity (UIEV) at 18 time points during the following 48 h. Iodine speciation in kombu was determined by liquid chromatography and inductively coupled plasma mass spectrometry (LC-ICPMS). 18 Chinese participants finally completed this study and two participants dropped out. The 0-24 h urinary iodine concentration (UIC) was consistently lower in the kombu group compared to the KI group (95 μg/L vs. 113 μg/L, p > 0.05; 109 μg/L vs. 223 μg/L, p < 0.001) at the interventions. The corresponding iodine bioavailability was significantly lower in the kombu supplement than in the KI (29.5% vs. 83.5%, p < 0.001; 23.7% vs. 63.7%, p < 0.001). The UIEV appeared to have distinct fluctuations, which exhibited a gradual increase for the kombu, reaching peaks of 22 and 25 μg/h, while demonstrating a steep surge for the KI, attaining higher peaks of 57 and 109 μg/h, respectively. The 50.9%-55.0% of total iodine in kombu was in inorganic iodide forms. This study showed a lower iodine bioavailability in participants receiving the kombu supplement compared to the KI. Furthermore, the UIEV demonstrated a moderate metabolic response following kombu intake, suggesting its potential as an alternative to iodized salt.