Analysis of iodine nutrition of people and serum thyroid hormone levels of women of childbearing age in pasturing areas of Tibet in 2009

Objective To explore the iodine nutrition level of people, prevalence of iodine deficiency disorders and the thyroid function of women of childbearing age in pasturing areas of Tibet. Methods Thirty families were selected respectively in pastoral Dangxiong county and agricultural Qushui county of Lhasa in 2009,drinking water and edible salt samples were collected to test iodine content; at least 50 people from each crowd of the following populations including children aged 8 - 10, women of childbearing age of 18 - 49 old and male adults aged 18 - 60 were randomly sampled and to measure their urinary iodine content and for thyroid palpation. Direct titrimetric method was used to test salt iodine(GB/T 13025.7-1999); As3+-Ce4+ oxidation reduction process to test water iodine (GB/T 5750.1-2006); As3+-Ce4+ catalytic spectrophotometry using ammonium persulfate digestion to test urine iodine(WS/T 107-2006), and goiter examination was based on "Diagnostic and Classificatory Criteria of Endemic Goiter" (WS 276-2007). Results The median of water iodine was 1.3 μg/L in pasturing area and 0.7 μg/L in agricultural areas, there was no statistical significant difference between them(Z =- 1.809, P ＞ 0.05).There was no iodized salt used in pastoral people, but iodized salt coverage rate was 90.0％(27/30) in agricultural residents. The median of urinary iodine among people of pasturing areas was 50.2 μg/L, lower than that of agricultural areas( 193.2 μg/L, Z =- 10.48, P ＜ 0.01 ). However, the goiter rate in pasturing area[1.0％(1/100)]was significantly lower than that of agricultural areas[18.0％(18/100) , x2 =16.8, P ＜ 0.01]. Serum level of FT4 and TT4 in pastoral population[(14.0 ± 2.0)pmol/L, (85.6 ± 17.5)nmol/L] was significantly lower than that of agricultural areas[(16.2 ± 6.3)pmol/L, (95.4 ± 21.1)nmoL/L, t =- 2.06, - 2.20, all P ＜ 0.05]. The thyroid dysfunction rate[5.9％ (2/34)]and subclinical hypothyroidism rate[2.9％ (1/34)]in pastoral population was significantly lower than that of agricultural areas[25.5％(12/47), 21.3％(10/47), x2 =5.328, 5.651, all P ＜ 0.05]. Conclusions Pastoral areas of iodine intake is significantly lower than the agricultural areas, urinary iodine levels reflect a serious iodine deficiency in pastoral people, but the blood biochemical and urinary iodine and goiter rate does not match,and shows hidden iodine hunger, which does not constitute a goiter epidemic. Key words: Iodine;  Deficiency diseases;  Urine;  Thyroid hormones