Investigation on iodine nutritional status and thyroid goiter prevalence of residents in Tianjin after salt iodination

Objective To investigate iodine nutritional status and thyroid goiter prevalence of residents in Tianjin after salt iodination. Methods From six districts, 31 530 residents and 4 415 pupils aged 7～14 years were selected by stratified cluster sampling. Their urinary iodine and iodine content of salt were measured. Their thyroid size and some children's 131 I thyroid uptake rate were also examined. Results The thyroid goiter prevalence were 1.7%～10.6% (average 5.5%) in residents, 12.3%～32.4% (average 22.7%) in children aged 7～14 years and 13.0%～27.7% (average 19.7%) in 8～10 years groups respectively. The goiter prevalence decreased considerably but slowly after iodized salt supply. In four districts, the median urinary iodine was 287.2 μg/L in residents and was 271.6 μg/L in children aged 8～10 years. The data showed that iodine nutrition of residents was adequate. The iodine content of salt from residents' kitchens was generally over 20 mg/kg and over 60 mg/kg in 9.9%～41.1% of salt samples, hence the high iodine content in iodized salt may become an unfavorable factor to the residents. Children's 131 I uptake rate was lower than before， which indicated that iodine deficiency has no more existed. Conclusions The iodine nutritional status improves ultimately after iodized salt supplementation for three years in Tianjin. Median urinary iodine and iodized salt reach the national standard for eliminating iodine defeciency disease but the goiter rate slowly decreased. The results indicate that iodine deficiency status is under control in Tianjin.