Iodine is an essential micronutrient for the production of thyroid hormones and its deficiecny remains a global problem impairing health. The primary source of iodine is the diet via consumption of foods, including cooked foods with iodized salt, dairy products, or naturally abundant seafood. Currently, the recommendation of dietary iodine intake is 150 μg per day in adults who are not pregnant or lactating. The ingestion of iodine or exposure above this threshold is well-tolerated and nearly no health problems are observed. The diets processed and cooked with iodized salt are generally important iodine sources, however, high iodine intake is a result of routine consumption of several kinds of edible algae in coastal regions, with varying contributions depending on the amount of seafood consumed.

Iodine absorption mainly depends on the iodine species in foods and possibly on the iodine status of the individual. Further, there was little available data on iodine absorption or bioavailability from different dietary sources, such as natutal kelp and fortified food with potassium iodide. To our knowledge, inorganic iodide is thought to be absorbed almost completely (over 90%). However, only about two-thirds of some forms of organically-bound iodine are absorbed. The different sources of iodine absorption have not been accurately quantified and compared in humans. Therefore, the purposes of this study were to quantify the iodine absorption of natural kelp in male and female adults and compare with the bioavailability from an iodine water solution (potassium iodide). This stduy will obtain the actual iodine bioavailability and the difference for different source of foods.

This study is a randomized, cross-over design and aims to evaluate the iodine bioavailability (measured using excretion in urine and fece) from different source and administered dose of iodine, such as natural kelp and potassium iodide delivering a dialy iodine intake about 600 µg and 1200 µg. This study will compare and measure to the ingestion of natural kelp and potassium iodide within one subject by three stages: (1) normal iodine intake stage (iodine intake >150 µg/day); (2) intervention stage, a bowl of soup with an extrinsic iodine dose of about 600 µg; or a bowl of natural kelp with a certain iodine content of about 1200 µg potassium iodide.

Inclusion Criteria:

• Aged between 18 and 25 years; BMI 19-25 kg/m2; Current use of iodized salt at home, adequate iodine nutritional status; Volunteer to participate in and comply with the requirement of study; Signed informed consent.

Exclusion Criteria:

• 1. Having history of thyroid diseases or thyroid dysfunction; 2. Inadequate iodine status (defined as mUIC <100 µg/L or >300 µg/L and assessed during screening by 3-days 24-h urine specimens) 3. Any metabolic, gastrointestinal or chronic disease or chronic use of medications or drug abuse 4. Use of iodine containing supplements within 1 month prior to study start or exposure to iodine-containing X-ray/ computed tomography contrast agent or often use of iodine-containing disinfectants 5. Cannot comply with the requirement of study or cannot delivered the excremental specimens on schedule

All, half male and half female