PURPOSE: Excess iodine in drinking water has emerged as a public health issue in China. This study assesses the effectiveness of removing iodized salt on reducing the iodine excess in populations living in high-iodine areas and also to identify the threshold value for safe levels of iodine in water. METHODS: Twelve villages from 5 cities of Hebei Province with iodine content in drinking water ranging from 39 to 313 µg/l were selected to compare the urinary iodine content of children aged 8-10 years before and after removing iodized salt from their diet. RESULTS: For 3 villages where median water iodine content (MWIC) was below 110 µg/l, following the removal of iodized salt (the intervention), the median urinary iodine content (MUIC) reduced to under 300 µg/l decreasing from 365, 380, 351 to 247, 240, 281 µg/l, respectively. However, the MUIC in the 9 villages with MWIC above 110 µg/l remained higher than 300 µg/l. The children's MUIC correlated positively with the MWIC in the 12 villages (p ≤ 0.001). The linear regression equation after removing iodized salt was MUIC = 0.6761MWIC + 225.67, indicating that to keep the MUIC below 300 µg/l (the iodine excess threshold recommended by the WHO) requires the MWIC to be under 110 µg/l. CONCLUSION: Removing iodized salt could only correct the iodine excess in the population living in the areas with MWIC below 110 µg/l. In the areas with water iodine above 110 µg/l, interventions should be focused on seeking water with lower iodine content. This study suggests a threshold value of 110 µg/l of iodine in drinking water to maintain a safe level of dietary iodine.
PURPOSE: Excess iodine in drinking water has emerged as a public health issue in China. This study assesses the effectiveness of removing iodized salt on reducing the iodine excess in populations living in high-iodine areas and also to identify the threshold value for safe levels of iodine in water. METHODS: Twelve villages from 5 cities of Hebei Province with iodine content in drinking water ranging from 39 to 313 µg/l were selected to compare the urinary iodine content of children aged 8-10 years before and after removing iodized salt from their diet. RESULTS: For 3 villages where median wateriodine content (MWIC) was below 110 µg/l, following the removal of iodized salt (the intervention), the median urinary iodine content (MUIC) reduced to under 300 µg/l decreasing from 365, 380, 351 to 247, 240, 281 µg/l, respectively. However, the MUIC in the 9 villages with MWIC above 110 µg/l remained higher than 300 µg/l. The children's MUIC correlated positively with the MWIC in the 12 villages (p ≤ 0.001). The linear regression equation after removing iodized salt was MUIC = 0.6761MWIC + 225.67, indicating that to keep the MUIC below 300 µg/l (the iodine excess threshold recommended by the WHO) requires the MWIC to be under 110 µg/l. CONCLUSION: Removing iodized salt could only correct the iodine excess in the population living in the areas with MWIC below 110 µg/l. In the areas with wateriodine above 110 µg/l, interventions should be focused on seeking water with lower iodine content. This study suggests a threshold value of 110 µg/l of iodine in drinking water to maintain a safe level of dietary iodine.