Abstract

Objective:
To assess the epidemiological patterns of thyroid dysfunction across different iodine nutritional statuses in residents of Gansu Province and to elucidate the relationship between iodine intake and the risk of thyroid disorders. Methods: In 2014, participants meeting the inclusion criteria were selected in Gansu Province using a multistage, stratified cluster random sampling method based on age and sex. A ten-year follow-up of the baseline cohort was conducted in 2024. The study comprised four main components: a structured questionnaire, physical examination, biochemical assessment of metabolic parameters, and thyroid ultrasonography. Fasting serum samples were collected to measure concentrations of thyroid-stimulating hormone (TSH), FT3, FT4, thyroid peroxidase antibody (TPOAb), and thyroglobulin antibody (TgAb). Urinary iodine concentration (UIC) was also assessed to evaluate iodine status. The prevalence of thyroid disorders was determined based on laboratory findings. Iodine nutritional status was classified according to urinary iodine concentration, and the association between iodine status and the risk of thyroid disorders was subsequently examined.
Results:
A total of 716 participants from Gansu Province were enrolled, including 72 with iodine deficiency, 473 with adequate iodine intake, and 170 with excessive iodine intake. The distribution of iodine nutritional status in 2014 was 10.07% deficient, 66.15% adequate, and 23.78% excessive, whereas in 2024, the corresponding proportions were 21.82%, 63.92%, and 14.41%, respectively. Over the ten-year period, a statistically significant increase in the proportion of individuals with iodine deficiency and a significant decrease in those with excessive iodine intake were observed (p < 0.001). No significant difference was found in the proportion of individuals with adequate iodine intake between the two survey years (p > 0.05). The prevalence of subclinical hypothyroidism differed significantly across iodine status groups, with rates of 17.95% (95% CI: 17.89–18.01) in the iodine-deficient group, 21.23% (95% CI: 21.19–21.26) in the iodine-sufficient group, and 17.48% (95% CI: 17.40–17.55) in the iodine-excess group (x^2= 8.374, p< 0.05). No statistically significant differences were found in the prevalence of overt hyperthyroidism, subclinical hyperthyroidism, overt hypothyroidism, or thyroglobulin antibody (TgAb) positivity among the different iodine status groups (p > 0.05).
Conclusion:
Over the past decade, there has been a significant improvement in the nutritional status of iodine among residents of Gansu Province. The observed substantial differences in the prevalence of subclinical hypothyroidism across varying iodine intake levels highlight the crucial role of iodine status in the pathogenesis of thyroid disorders.