A 4-week study was conducted in 25 Chinese euthyroid women. Unified diets with different iodine contents (cooked with non-iodized salt or iodized salt) were provided in two different periods. The total iodine intake from diet, water and air as well as the total iodine excretion by urine, faces and respiration were monitored and determined, and a total of 300 samples were collected. The sweat iodine loss was also considered. Moreover, the regression curve model between the 24-h iodine intake and 24-h iodine excretion was also established.

The experiment was conducted between November and December with a total duration of 1 month. Referring to the experience from Harrison and Dworkin, however, considering the negative iodine balance reported, during the first 3 weeks, the diet was provided with non-iodized salt, while the diet with iodized salt was only offered in the last week. The total daily iodine intake consisted of dietary iodine intake, water iodine intake and iodine from breathing, while iodine could be excreted out of human body by urine, faces, sweat and breathing. The 24-h iodine intake and 24-h iodine excretion were determined in each individual participant, and the iodine balance was calculated accordingly.

Inclusion Criteria:

• The ones with normal thyroid function, urinary iodine concentration, agree with the experiment.

Exclusion Criteria:

• The ones with abnormal thyroid hormone level, urinary iodine concentration (UIC) or autoantibody-positive were excluded from the study.