Assessing the impact of drinking water iodine concentrations on the iodine intake of Chinese pregnant women living in areas with restricted iodized salt supply

PURPOSE

The supply of non-iodized salt and the water improvement project have been conducted to reduce the iodine concentration in drinking water in areas with elevated water iodine. We aimed to assess the impact of water iodine concentration (WIC) on the iodine intake of pregnant women in areas with restricted iodized salt supply, and determine the cutoff values of WIC in areas with non-iodized salt supply.

METHODS

Overall, 534 pregnant women who attended routine antenatal outpatient visits in Zibo Maternal and Child Health Hospital in Gaoqing County were recruited. The 24-h urine iodine excretion (UIE) in 534 samples and the iodine concentration in 534 drinking water samples were estimated. Urinary iodine excretion, daily iodine intake, and daily iodine intake from drinking water (WII) were calculated. The relationship between WIC and daily iodine take was analyzed.

RESULTS

The median WIC, spot urine iodine concentration (UIC), and 24-h UIE were 17 (6, 226) μg/L, 145 (88, 267) μg/L, and 190 (110, 390) μg/day, respectively. A significant positive correlation was found between WIC and UIE (R² = 0.265, p < 0.001) and UIC (R² = 0.261, p < 0.001). The contribution rate of WII to total iodine intake increased from 3.0% in the group with WIC of < 10 μg/L to 45.7% in the group with WIC of 50-99 μg/L.

CONCLUSION

The iodine content in drinking water is the major iodine source in pregnant women living in high-water iodine areas where iodized salt supply is restricted. The contribution rate of daily iodine intake from drinking water increases with the increase in water iodine concentration.

Reproducible and reliable general semiquantitative food frequency questionnaire for evaluating iodine intake in Chinese children

Iodine deficiency is a global issue that is correlated with a variety of diseases and can affect individuals of all ages. We hypothesized that a general, semiquantitative food frequency questionnaire (FFQ) could be a valuable tool to evaluate iodine intake in children. Study participants comprised 687 healthy children between the ages of 7 and 13 years. The FFQ was developed to assess habitual iodine intake over a 6-month period (FFQ1). A 3-day estimated food diary (3DEFD) and the habitual daily iodine intake, calculated from 2-repeated 24-hour urine iodine excretion, tested the intermethod relative validity of the FFQ. There were 92 children who also repeated the FFQ (FFQ2) 3 weeks later to assess for FFQ reproducibility. Iodine intake estimated by FFQ1 + water was significantly higher than that indicated by the 3DEFD + water (204 μg/d vs 156 μg/d, P < .001), whereas there were no differences between habitual daily iodine intake and FFQ1 + water (185 μg/d vs 204 μg/d, P = .223). The interclass correlation coefficients of iodine intake estimated by the FFQ1 and FFQ2 were 0.72 (P < .001). The FFQ1 + water was moderately correlated with the 3DEFD + water (Spearman correlation coefficient = 0.57, P < .001) as well as habitual daily iodine intake (SCC = 0.34, P < .001). The subjects classified into the same or adjacent quartiles ranged from 32% to 93%. The κ value α was 0.46 for FFQ1 and FFQ2 (P < .001) 0.27 for FFQ1 + water and 3DEFD + water (P < .001), and 0.09 for FFQ1 + water and habitual daily iodine intake (P < .001). The results showed this FFQ is a reliable and reproducible tool in evaluating iodine intake in Chinese children.