OBJECTIVETo evaluate the influence of different salt iodine concentration on urinary iodine excrition among the target population and to determine the appropriate level of salt iodization to the local people.

METHODSIn the 31-day random control trial, 1099 subjects from 399 families were randomly distributed into four groups and were supplied with iodized-salt with different iodine concentration of (6 +/- 2)mg/kg, (15 +/- 2)mg/kg, (24 +/- 2)mg/kg and (34 +/- 2)mg/kg, respectively. The original family salt was retrieved, whose iodine content was determined in those subjects' families with single-blind method. Baseline survey was conducted including salt and urinary iodine of the subjects. From the 27th day after the intervention, the urinary samples of the subjects were continuously collected for 5 days and urinary iodine was tesed respectively. Meanwhile, daily meal investigation was conducted to evaluate the influences originated from food.

RESULTSThe median of local water iodine content was 3.05 microg/L and the average salt iodine concentration was (36.4 +/- 5.4)mg/kg while 98.8% of the household consumed sufficient iodized-salt. The medians of baseline urinary iodine of the subjects were 293.6 microg/L in city, and 508.8 microg/L in the countryside. The urinary iodine medians of four groups in the day of 28th after intervention were 97.2 microg/L, 198.6 microg/L, 249.4 microg/L, and 330.7 microg/L respectively in the city group, while they were 100.5 microg/L, 193.0 microg/L, 246.3 microg/L and 308.3 microg/L seperately in the countryside group. There was no statistically significant differences among the medians of urine iodine in the 27th, 28th, 29th, 30th and 31st day after intervention (P > 0.05).

CONCLUSIONSThe target areas were with iodine deficiency which possessed high coverage of qualified iodized-salt at household level. The average urinary iodine level of the subjects was slightly higher than the standard level, according to the baseline survey. The intervetion trail showed that the salt iodine concentration of 15-24 mg/kg was sufficient to the local people.