Résumé
Objective To access the effectiveness of withdrawing iodized salt on correcting the iodine excess in the population living in high iodine areas.Methods Before withdrawing iodized salt,2 twons were selected from each of 5 cities with water-borne iodine excess areas in Hebei province.All the selected towns were divided into 7 groups according to their iodine content in drinking water.Two villages wereselected from each group where urine samples of children aged 8 to 10 years old were collected to investigate the change of urinary iodine content of these children before and after withdrawing iodized salt.The urinary iodine content was determined using the method for determination of ammonium persulfate digestion arsenic cerium catalytic spectrophotometry (WS/T 107-2006).Correlation between children's urinary iodine and drinking water iodine was analyzed.Results Before and after withdrawing iodized salt,744 and 771 urine samples were collected from the examined children aged 8-10 years respectively.The overall median urinary iodine content (MUIC) of the examined children after withdrawing iodized salt (350.1 μg/L) decreased significantly than that of before withdrawing iodized salt (460.8 μg/L,U =3 127.8,P ＜ 0.05).After withdrawing iodized salt,the MUIC of the children decreased significantly in 8 of 12 villages (P ＜ 0.05).Before and after withdrawing iodized salt,the percentage of urine samples with iodine content above 300 μg/L was 76.7％ (571/744),58.5％ (451/771) respectively,with significant statistical difference (x2 =57.7,P ＜ 0.05).After withdrawing iodized salt,Children's MUIC also decreased significantly across gender and age (boys:558.5,351.6 μg/L,U =960,P ＜ 0.05; girls:522.9,355.5 μg/L,U =698,P ＜ 0.05; 8 years old:536.0,295.5 μg/L,U =529.5,P ＜ 0.01; 9 years old:386.2,323.2 μg/L,U =753.5,P ＜ 0.01; 10 years old:525.5,368.8 μg/L,U =521.5,P ＜ 0.05).The children's MUIC correlated positively with the median water iodine contert (MWIC) in the villages where they lived (r =0.951,P ＜ 0.01).Analyzed by linear regression,approximately 89％ of the variability in MUIC was associated with variability in MWIC.Conclusions Withdrawing iodized salt could only correct the iodine excess caused by consuming iodized salt in the population living in the areas with MWIC below 100 μg/L.In the areas with water iodine above 100 μg/L,intervention should be focused on seeking water with proper iodine content.