Iodine nutrition and thyroid function in different populations after 20 years of universal salt iodization in iodine deficiency area of Shanxi Province / 中华地方病学杂志

ABSTRACT

Objective To understand the iodine nutritional status and thyroid function of different populations after 20 years of universal salt iodization in iodine deficiency area of Shanxi Province, and to provide data support for scientific iodine supplementation according to local conditions. Methods In 2014, six townships (Chengguan, Dadeng, Dengzhuang, Gucheng, Xiangling and Fencheng townships) in Xiangfen County, Linfen City, Shanxi Province, were selected as the place of investigation. Four hundred school-age children aged 6 - 12 years (school-age children), 400 child-bearing women aged 18 - 44 (child-bearing women), 400 pregnant women, 400 lactating women and their 0 - 6 months breast-feeding infants (breast-feeding infants), and 400 children aged 7 -24 months were selected by two-stage sampling method. Water samples of school-age children's domestic drinking water and salt samples for domestic consumption were collected, and the water iodine and salt iodine were detected by arsenic and cerium catalytic spectrophotometry ( recommended by the National Iodine Deficiency Disorders Reference Laboratory) and "General Test Method in Salt Industry-Determination of Iodine" (GB/T 13025.7-2012). Random urine samples of all subjects were collected, urine iodine was detected by "Method for Determination of Iodine in Urine by As3+-Ce4+ Catalytic Spectrophotometry" ( WS/T 107-2006 ) . Samples of filter paper dried blood spots (DBS) of school-age children, child-bearing women, pregnant women, lactating women and breast-feeding infants were collected, and serum total thyroxine (TT4) and thyroid stimulating hormone (TSH) levels were detected by time-resolved fluorescence immunoassay. Results A total of 290 water samples were collected, and the median of water iodine was 9.37μg/L. A total of 406 salt samples were collected, the median of salt iodine was 25.0 mg/kg, the coverage rate of iodized salt was 98.52％ (400/406), and the consumption rate of qualified iodized salt was 92.61％ (376/406). Urine samples of 389 school-age children, 379 child-bearing women, 363 pregnant women, 365 lactating women, 366 breast-feeding infants, and 366 children aged 7 - 24 months were collected, and the medians of urine iodine were 200.7, 175.0, 186.0, 113.2, 285.8 and 204.8 μg/L, respectively. Among them, school-age children, breast-feeding infants, and children aged 7-24 months were over the appropriate level, while the rest populations were at the iodine appropriate levels. Blood samples of 402 school-age children, 397 child-bearing women, 398 pregnant women, 390 lactating women, and 386 breast-feeding infants were collected, and the medians of TT4 were 127.2, 110.2, 141.7, 95.8 and 139.0 nmol/L, respectively; the medians of TSH were 1.2, 0.9, 0.8, 0.9 and 0.9 mU/L, respectively, and they were all within the reference ranges. The abnormal rates of TT4 (8.46％, 33/390) and TSH (7.95％, 31/390) in lactating women were higher than those in school-age children, child-bearing women, pregnant women and breast-feeding infants [TT4 abnormal rates were 0.25％(1/402), 1.26％ (5/397), 0.50％ (2/398), 1.04％ (4/386), respectively; TSH abnormal rates were 1.24％ (5/402), 1.51％ (6/397), 1.51％ (6/398) and 0.78％ (3/386), respectively, P < 0.05]. The rate of thyroid dysfunction in lactating women (7.95％, 31/390) was higher than those in the rest populations [1.24％ (5/402), 1.51％ (6/397), 1.51％ (6/398), 0.78％ (3/386), P < 0.05]. Conclusions The iodine intake of different populations in the survey area is generally sufficient, and the current salt iodine content standard can meet the iodine nutrition needs of different populations. Lactating women have a high rate of thyroid dysfunction. It is suggested to stick to the strategy of universal salt iodization to prevent iodine deficiency hazards in iodine deficiency areas, and further strengthen the monitoring of iodine nutrition and thyroid function of pregnant women and lactating women.