Relationship of household cooking salt and eating out on iodine status of pregnant women in environmental iodine-deficient coastal areas of China

Iodine Status of Infants and Toddlers under 2 Years of Age and Its Association with Feeding Behaviors and Maternal Iodine Status in Shanghai: A Quantile Regression Analysis

It is crucial to provide adequate iodine nutrition to infants and toddlers for proper thyroid function and subsequent brain development. Infants are particularly vulnerable to iodine deficiency during the transition from a milk-based diet (breast milk and/or infant formula) to solid food. This study examines the current iodine levels of children during their first two years of life and investigates the association between these levels and feeding behaviors and the iodine status of their mothers in Shanghai, a city located in eastern China. A hospital-based cohort study was conducted to enroll mother-child pairs, where the child is aged 6-23 months, who visited community health service centers in the 16 districts of Shanghai, China. Data on socio-demographic factors and feeding behavior data were collected from the participants. The urinary iodine concentration (UIC) in both the young children and their mothers were analyzed. A total of 2282 mother-child pairs were included in this analysis. The median (p25-p75) UIC for lactating women, weaning women, and children were 121.3 μg/L (68.1-206.4 μg/L), 123.4 μg/L (58.4-227.2 μg/L), and 152.1 μg/L (75.8-268.3 μg/L), respectively. The UIC in children was found to be higher than that in their mothers (p < 0.001). Children who consumed less than 500 mL per day of formula milk in the last week had lower UICs compared with those who consumed 500 mL per day or more (p = 0.026). Furthermore, the children's UIC was positively correlated with the maternal UIC (rs = 0.285, p < 0.001). Multiple quantile regression analysis revealed a statistically significant positive association between maternal UIC and children's UIC between the 0.1 and 0.9 quantiles (all p < 0.001). We found that the iodine status of infants and toddlers, as well as of mothers, was sufficient. However, a large minority of children and mothers may be at risk of iodine deficiency. Furthermore, no associations between children's UIC and feeding behaviors were observed. Moreover, there was a positive correlation between the UIC of young children and their mothers.

Iodine Excess May Lead to Low Exam Score in Children Aged 8-10 Years

Recent research has shown that iodine excess may damage children's intelligence. Years of monitoring results in Shanghai show the iodine status has approached the upper limit of the appropriate range for children aged 8-10 years, indicating a risk of iodine excess. We used multi-stage random sampling to select children. Sixteen districts of Shanghai were divided into five units based on geographic location, and one primary school was randomly selected from each unit. In each selected school, about 40 children aged 8-10 years were randomly recruited to measure their urinary iodine concentration (UIC), household salt iodine concentration (SIC), the score of the final unified exam of the last semester, and school canteen salt iodine concentration. The median UIC of 3213 children aged 8-10 years in Shanghai was 195.4 (122.0, 285.8) µg/L and exceeded 200 µg/L in 48.8% of the population. Household and school canteen iodized salt coverage rates were 60.3% and 82.5% respectively, and mean household and school canteen SICs were 21.51 ± 9.30 mg/kg and 25.29 ± 3.40 mg/kg respectively. By correcting for potential confounding factors, logistic regression demonstrated that compared to the adequate iodine status group, students in the slight iodine excess group were less likely to get "A" (score > 90) in math, Chinese, and English exams (Math: OR = 0.775, 95% CI = 0.660-0.911, P = 0.002; Chinese: OR = 0.707, 95% CI = 0.543-0.842, P < 0.001; English: OR = 0.720, 95% CI = 0.610-0.849, P < 0.001). In Shanghai, the iodine status of 8-10-year-old children is approaching the upper limit of the adequate range. Iodine excess in Shanghai may lead to low exam scores for students.

Serum iodine concentration and its associations with thyroid function and dietary iodine in pregnant women in the southeast coast of China: a cross-sectional study

Background

Iodine deficiency is a major public health problem in pregnant women. Serum iodine (SI) may represent a useful biomarker for iodine nutrition evaluation. We aimed to assess the relationship between serum iodine concentration (SIC) and urinary iodine concentration (UIC), dietary iodine, thyroid function, and thyroid diseases in pregnant women in the southeast coast of China, and to provide a normal reference range of SIC for pregnant women.

Methods

A multistage random sampling method was used to select the study population. We collected urine and blood samples from pregnant women and determined UIC and SIC as well as thyroid function using Arsenic-Cerium Catalytic Spectrophotometry, inductively coupled plasma mass spectrometry, and Beckman Coulter Access2 chemiluminescent immunoanalyzer and kit, respectively, and administered a questionnaire on dietary iodine intake in pregnant women.

Results

There was a significant negative correlation between SI and thyroid-stimulating hormone (TSH) (r = -0.141) and a significant positive correlation between SI and free triiodothyronine (FT3) (r = 0.106), free thyroxine (FT4) (r = 0.236), triiodothyronine (TT3) (r = 0.229), total thyroxine (TT4) (r = 0.433), and dietary iodine intake (r = 0.068). There was a significant difference in SI levels of pregnancy between the second (78.13 μg/L) and third trimester (75.37 μg/L) (p = 0.018). SI levels between inadequate intake (74.58 μg/L) and appropriate intake (77.92 μg/L) groups were statistically different (p = 0.036). Low SIC was a risk factor for the development of hypothyroxinemia (adjusted OR = 3.14, 95% confidence interval: 1.75-5.66). The reference range for SIC in normal pregnant women is 45.03-112.44 μg/L.

Conclusion

SI may be a composite indicator of iodine nutritional status and thyroid function.

A Cross-Sectional Survey of Iodized Salt Usage in Dining Establishments - 13 PLADs, China, 2021-2022

What is already known about this topic?

The National Iodine Deficiency Disease Surveillance system is exclusively focused on monitoring cooking salt used within households. Currently, there is a lack of nationally representative data on the use of iodized salt in dining establishments.

What is added by this report?

This study evaluated 7,889 salt samples obtained from dining establishments located in 13 provincial-level administrative divisions across China. The findings indicated that coverage rate of iodized salt (CRIS) and the consumption rate of adequately iodized salt (CRAIS) were found to be 95.2% and 90.2%, respectively. Further, 880 samples were classified as iodized salt and 804 as adequately iodized salt. In coastal areas, the CRIS and CRAIS showed a significant decrease to 77.1% and 70.5%, respectively, when compared to the inland regions (P<0.01).

What are the implications for public health practices?

The data compiled could potentially fill the void in the national data concerning the use of iodized salt in dining establishments throughout China. It is of the utmost importance to increase the awareness of restaurant operators, particularly those located in coastal areas, about the benefits of iodine supplementation. Moreover, they should be encouraged to use adequately iodized salt.

Association of maternal thyroid dysfunction and autoimmunity with adverse birth outcomes

This study aimed to explore the relationship between thyroid function and autoimmunity and adverse birth outcomes. Serum levels of thyroid function were detected by electrochemiluminescence assay. Urine iodine concentration was detected using the acid digestion method. We used multiple linear regression to assess the correlation between thyroid function indicators and birth weight according to trimester stratification and binary logistic regression to evaluate the correlation between thyroid dysfunction and adverse birth outcomes. Reference ranges for trimester-specific thyroid hormones were established in our 2564 pregnant women cohort with mild iodine deficiency. The higher the maternal thyroid-stimulating hormone in the first trimester (B = 0.09, P = 0.048) and total triiodothyronine (TT3) in the third trimester (B = 0.16, P < 0.001) of TPOAbnegative women, the higher the birth weight Z-score, whereas in the second trimester, free-thyroxine of mothers with TPOAb negative was lower (B = -0.10, P = 0.026) and the birth weight Z-score was higher. Pregnant women with overt and subclinical hyperthyroidism had a higher risk of preterm births than euthyroid women (11.9% vs 4.5%; odds ratio (OR): 2.84; P = 0.009). Women with higher TT3 had a higher risk of preterm (17.0% vs 4.5%; OR: 4.19; P < 0.001) and LGA (34.0% vs 11.1%; OR: 3.70; P < 0.001) births than euthyroid women. In conclusion, thyroid function during pregnancy could affect birth weight and birth outcome.

Iodine in household cooking salt no longer plays a crucial role in iodine status of residents in Tianjin, China

PURPOSE

The contribution of household cooking salt to population iodine status is decreasing in China, the applicability of the coverage rate of iodized salt (IS), proportion of adequately iodized salt (AIS), and salt iodine concentration (SIC) of household cooking salt used for iodine status assessment of residents requires further investigation.

METHODS

Through the IDD control project, 16,445 children and 4848 pregnant women were recruited from Tianjin, China and the relationship between the coverage rate of IS, proportion of AIS, SIC, and population iodine status was analyzed. Additionally, through the thyroid health survey project, 856 children with IS or noniodized salt were recruited. The effects of different household cooking salts on individual iodine status and thyroid health were analyzed.

RESULTS

After adjusting for confounding factors, no relationship was found between the coverage rate of IS, proportion of AIS, SIC of household cooking salt, and iodine status of children and pregnant women (all P > 0.05). No differences in levels of thyroid function and structural indicators were found in children with different household cooking salts (all P > 0.05). Additionally, no relationship was found between noniodized salt exposure and goiter, overt hyperthyroidism, overt hypothyroidism, thyroid nodules, antibody single positivity, or subclinical hypothyroidism (all P > 0.05).

CONCLUSION

Iodine in household cooking salt no longer plays a crucial role in iodine status in Tianjin, China. Other indicators must be identified as beneficial supplements for precise iodine status evaluation not only in Tianjin but also in other large cities in China.