A cross-sectional comparison study on the iodine nutritional status between rural and urban residents in Zhejiang Province, China

OBJECTIVES: To evaluate the difference of iodine nutritional status between rural and urban residents under the universal salt iodisation policy. SETTING: A multistage cluster sampling technique was employed in the present cross-sectional study. In total, 3300 rural and 3300 urban households were selected where the investigation was conducted. PARTICIPANTS: A total of 8553 rural and 8909 urban residents participated in this provincial survey. PRIMARY AND SECONDARY OUTCOME MEASURES: Spot urine samples were collected and the iodine concentration in urine was determined by the modified acid-digestion method. RESULTS: The median urinary iodine concentration of rural residents was 170.1 μg/L, which was higher than that of urban residents with 153.5 μg/L. For school-aged children, middle-aged people and older people, the median urinary iodine concentration of rural residents was 191.2, 160.2 and 154.0 μg/L, respectively, which was higher than that of urban residents with 166.2, 153.8 and 129.5 μg/L, respectively. Risk factors for urinary concentration of rural residents were age (OR=0.99), terrain (OR=0.83), usual intake of pickled products (OR=1.45) and non-iodised salt intake (OR=0.39), while those for urban residents were age (OR=0.99), terrain (OR=0.83), usual intake of aquatic products (OR=1.24) and non-iodised salt intake (OR=0.27) compared with iodised table salt intake. CONCLUSIONS: The median urinary iodine concentration of rural residents was higher than that of urban residents although they were both falls in optimal iodine status as recommended by WHO/UNICEF/International Council for the Control of Iodine Deficiency Disorders. Iodised salt intake is the major factor which influences the iodine nutritional status mostly for rural and urban residents. The ongoing monitoring of population iodine status remains crucially important.