Causes of different goiter rates with the same iodine deficiency among the pastoral and agricultural populations of Tibet: a geographical comparison.

BACKGROUND: The residents of both the agricultural and pastoral areas of Tibet share the same iodine deficiency and iodine nutrition, but the rate of thyroid goiter was significantly higher in the agricultural areas than in the pastoral areas. This project sought to determine why the populations in the iodine-deficient pastoral areas show a lower rate of thyroid goiter. METHODS: Food frequency questionnaires (FFQs) and 24 h history recalls were adopted to investigate the dietary patterns of the residents of the agricultural and pastoral areas. Meat and milk samples were collected to measure their inorganic iodine, total iodine and thyroid hormone contents using ICP-MS, AsIII-Ce4+ catalytic spectrophotometry and the Siemens' chemiluminescence method, respectively. The intake of protein, and the microelements, selenium and iron, was calculated according to their content in the food. RESULTS: The per capita daily intake of meat, dairy, and cereal in the pastoral areas was 116.7, 216.7, and 433.3 g, respectively, which are significantly higher than those in the agricultural areas (50.0, 72.2, and 375.0 g, respectively) (p < 0.05). The content of thyroid hormone in dried beef and milk in the pastoral areas was 62.6 and 13.5 µg/kg, respectively, which was significantly higher than those in the agricultural areas (25.1 and 4.1 µg/kg, respectively) (p < 0.05). The daily intake of thyroid hormone, protein and microelements, selenium and iron from foods by the residents of the pastoral areas were 10.5 µg, 99.6 g, 30.0 µg and 15.8 mg respectively, which was significantly higher than those in the agricultural areas (1.79 µg, 56.5 g, 23.8 µg and 13.2 mg, respectively) (p < 0.05). CONCLUSIONS: The significantly high intake of the food-borne thyroid hormone by the residents of the pastoral area could be the main reason the residents in the pastoral areas show a lower rate of thyroid goiter than those in the agricultural area. Moreover, the relatively high intake of protein and trace elements, selenium and iron by residents in the pastoral area could be another important factor for reducing the goiter rates.

An iodine balance study to explore the recommended nutrient intake of iodine in Chinese young adults.

Data on average iodine requirements for the Chinese population are limited following implementation of long-term universal salt iodisation. We explored the minimum iodine requirements of young adults in China using a balance experiment and the 'iodine overflow' hypothesis proposed by our team. Sixty healthy young adults were enrolled to consume a sequential experimental diet containing low, medium and high levels of iodine (about 20, 40 and 60 µg/d, respectively). Each dose was consumed for 4 d, and daily iodine intake, excretion and retention were assessed. All participants were in negative iodine balance throughout the study. Iodine intake, excretion and retention differed among the three iodine levels (P < 0·01 for all groups). The zero-iodine balance derived from a random effect model indicated a mean iodine intake of 102 µg/d, but poor correlation coefficients between observed and predicted iodine excretion (r 0·538 for µg/d data) and retention (r 0·304 for µg/d data). As iodine intake increased from medium to high, all of the increased iodine was excreted ('overflow') through urine and faeces by males, and 89·5 % was excreted by females. Although the high iodine level (63·4 µg/d) might be adequate in males, the corresponding level of 61·6 µg/d in females did not meet optimal requirements. Our findings indicate that a daily iodine intake of approximately half the current recommended nutrient intake (120 µg/d) may satisfy the minimum iodine requirements of young male adults in China, while a similar level is insufficient for females based on the 'iodine overflow' hypothesis.

Evaluation of median urinary iodine concentration cut-off for defining iodine deficiency in pregnant women after a long term USI in China.

BACKGROUND: The WHO/UNICEF/ICCIDD define iodine deficiency during pregnancy as median urinary iodine concentration (MUIC) ≤ 150 µg/L. China implemented universal salt iodization (USI) in 1995, and recent surveillance showed nationwide elimination of iodine deficiency disorders (IDD). Data from 2014 showed that the MUIC in 19,500 pregnant women was 154.6 µg/L and 145 µg/L in 9000 pregnant women in 2015. However, symptoms of iodine deficiency were absent. Our study sought to evaluate whether MUIC below 150 µg/L affects thyroid function of Chinese pregnant women and their newborns in Chinese context. METHODS: We screened 103 women with normal thyroid function and MUIC lower than 150 µg/L during week 6 of pregnancy at Peking Union Medical College Hospital. Patient demographics and dietary salt intake were recorded. Subjects were followed at 12, 24, and 32 gestational weeks. At each visit, a 3-day dietary record, drinking water samples, and edible salt samples were collected and analyzed for total dietary iodine intake. Additionally, 24-h urine iodine and creatinine were measured. Blood tests assessed thyroid function in both mothers and newborns. RESULTS: Of 103 pregnant women enrolled, 79 completed all follow-up visits. Most subjects maintained normal thyroid function throughout pregnancy. However, 19 had thyroid dysfunction based on thyroid stimulating hormone and free thyroxine levels. The median serum iodine was 71 µg/L (95% CI: 44, 109). The median thyroglobulin was < 13 µg/L. values above this level indicate iodine deficiency in pregnant women. The median dietary iodine intake during pregnancy, derived from the 3-day record and measures of water and salt, was 231.17 µg/d. Assuming 90% urinary iodine excretion (UIE), 200.11 µg/d UIE means the 222.34 µg iodine loss per day, suggesting that subjects had a positive iodine balance throughout pregnancy. All neonatal blood samples showed TSH levels lower than 10 mIU/L, indicating normal thyroid function. No significant difference was found among gestational weeks for urinary iodine, and the MUIC in subjects who completed 3 follow-up visits was 107.41 µg/L. CONCLUSION: Twenty years after implementing USI, expectant Chinese mothers with MUIC of 107.4 µg/L, less than the WHO's 150 µg/L benchmark, maintained thyroid function in both themselves and their newborn babies.

Analysis of potassium iodate reduction in tissue homogenates using high performance liquid chromatography-inductively coupled plasma-mass spectrometry.

Potassium iodate (KIO3) and potassium iodide (KI) are the major salt iodization agents used worldwide. Unlike iodide (I(-)), iodate (IO3(-)) should be reduced to I(-) before it can be effectively used by the thyroid. In this study, we developed a new method for analyzing IO3(-) and I(-) in tissue homogenates using high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC-ICP-MS). We further applied the method to demonstrate the KIO3 reduction process by tissues in vitro. The effects of KIO3 on the total antioxidative activity (TAA) and reduced nicotinamide adenine dinucleotide phosphate (NADPH) were also investigated here. Finally, we found that IO3(-) can be reduced to I(-) by tissue homogenates and IO3(-) irreversibly decreases the antioxidant capability of tissues. Our studies suggest that KIO3 might have a big effect on the redox balance of tissue and would further result in oxidative stress of organisms.

Is the current iodine content in edible salt appropriate for eliminating iodine deficiency in China.

OBJECTIVE: This study was designed to measure the urinary iodine excretion of volunteers who daily consumed iodized salt and to evaluate whether the current iodine content in salt is appropriate. A field trial study was then conducted to determine how the salt iodization content should be adjusted, either to prevent iodine deficiency or to avoid excess consumption. METHODS: A total of 1,099 volunteers from 399 households from urban and rural regions were selected. The levels of salt iodine and urinary iodine were measured prior to the field trial. All the households were randomly divided into four groups according to different salt iodine concentrations: group A, 6+/-2 mg/kg; group B, 15+/-2 mg/kg, group C, 24+/-2 mg/kg; and group D, 34+/-2 mg/kg. The urinary iodine levels of households were determined over five consecutive days, starting on the 27th day after the intervention. RESULTS: Before the intervention, the median urinary iodine excretions for urban and rural residents are 294 microg/L and 509 microg/L, respectively. By contrast, urinary iodine excretion in all groups significantly declined after the intervention. The median excretions of urinary iodine on the 28th day after the intervention for all groups were 97.2 microg/L, 199 microg/L, 249 microg/L and 331 microg/L for urban residents, and 101 microg/L, 193 microg/L, 246 microg/L and 308 microg/L for their rural counterparts, respectively. CONCLUSIONS: The trial exhibits a tendency of slightly excessive iodine intake among the households under the currently recommended standard.

[A pilot study on the feasibility of simplified scheme of national iodized salt monitoring program].

OBJECTIVE: To draft out the simplified scheme of iodized salt monitoring program to compare with the current scheme, and to study its feasibility. METHODS: 8 counties from 4 provinces were selected at different coverage rate of iodized salt. Conduct the monitoring program using the current scheme and the simplified scheme, then compare the results. RESULTS: The monitoring results of the current scheme showed the coverage rate of iodized salt and adequate iodized salt were 88.1% and 84.8% and the data of the simplified scheme were 85.2% and 79.8% respectively. Five counties reached above 90% of both the coverage rates of iodized salt and adequate iodized salt and the results showed no significant difference between the two schemes. The rates of other three counties were low, and the difference was significant between Dulan and Linxia counties. To the whole samples, the difference was also significant. CONCLUSION: The simplified scheme could be applied to those that the coverage rate of iodized salt was quite high or the non-iodized salt was well-distrbuted. However, for those areas with low coverage rate, it might not be suitable. As for the whole nation, it might not be popularized due to the gap of coverage rate between western and eastern areas.