Iodine Nutrition and the Prevalence of Thyroid Disease after Salt Iodization: A Cross-Sectional Survey in Shanghai, a Coastal Area in China

Abstract

BackgroundBoth insufficient and excess iodine may produce thyroid disease. After salt iodization in China, the median urine iodine concentration (UIC) of children aged 8–10 years appeared adequate. However, it is unknown whether dietary changes due to rapid economic development in Shanghai have affected whole population iodine nutrition.ObjectiveTo assess dietary iodine intake, UIC and the prevalence of thyroid disease in the general population of Shanghai.DesignA cross-sectional survey was conducted with general participants aged 5–69 years (n = 7,904) plus pregnant and lactating women (n = 380 each) selected by stratified multistage sampling. The iodine concentrations in their salt, drinking water and urine were measured. Daily iodine intake was estimated using the total diet study approach. Serum thyroid hormone concentrations and thyroid-related antibodies were measured and thyroid ultrasonography was performed.ResultsThe median iodine concentration in salt was 29.5 mg/kg, and 12.8 µg/L in drinking water. Iodized salt, used by 95.3% of participants, contributed 63.5% of total dietary iodine. Estimated daily iodine intake was 225.96 µg. The median UIC of general participants was 146.7 µg/L; UIC <100 µg/L (iodine insufficiency) was seen in 28.6%; UIC >300 µg/L (iodine excess) in 10.1%. Pregnant women had a median UIC of 135.9 µg/L, with UIC <150 µg/L in 55.4%. Thyroid nodules and subclinical hypothyroidism were found in 27.44% and 9.17%, respectively.ConclusionsAccording to published criteria, the current dietary iodine intake in Shanghai was generally sufficient and safe, but insufficient in pregnant women. Thyroid nodules and subclinical hypothyroidism were the commonest thyroid diseases identified.

Reference intervals of thyroid hormones in a previously iodine-deficient but presently more than adequate area of Western China: a population-based survey

“…The intra-and interassay coefficients of variation (CV) were lower than 4.8% for the TSH values ranging from 0.008 to 150 mIU/L. The FT 4 , FT 3 , T 3 , T 4 , TPO-Ab and Tg-Ab mones. China initiated the program of Universal Salt Iodization (USI) in 1996, and most areas of the country have become iodine sufficient since the year of 2000 [5].…”

“…The corresponding normal levels of serum TSH, FT 4 , FT 3 , T 4 , T 3 , TPO-Ab and Tg-Ab provided by the manufacturers were 0.55-4.78 mIU/L, 11.5-22.7 pmol/L, 3.5-6.5 pmol/L, 58.1-140.6 mmol/L, 0.92-2.79 mmol/L, 0-60 U/mL and 0-60 U/mL, respectively.…”

“…The serum samples were stored at -80ºC until the measurement for TSH, FT 4 , FT 3 , T 3 , T 4 , TPO-Ab and Tg-Ab levels. All serum samples were measured by using electrochemiluminescence immunoassays (ADVIA Centaur ® XP, Siemens Healthcare Diagnostics Inc., Tarrytown, NY).…”

“…The association of iodine intake with the occurrence of thyroid disease is U-shaped [4]. Either iodine deficiency or iodine more than adequacy has great impact on determination of the RIs of thyroid hor-September 2013.…”

Moderate iodine deficiency among pregnant women in Hong Kong: revisit the problem after two decades

“…28 Nonetheless dietary iodine intake remains insufficient among pregnant women in Shanghai, Zhejiang, and other coastal cities where iodine is considered sufficient for the general population. 29,30 A national survey from the Mainland reported that the median UIC levels of pregnant and lactating women were 123-224 μg/L and 109-224 μg/L, respectively; median UIC was higher among those in inland cities, because of a higher iodine level in the salt and greater household coverage. 31 In contrast, the progress in tackling iodine insufficiency in Hong Kong has been far from satisfactory.…”