Estimated change in prevalence of abnormal thyroid-stimulating hormone levels in China according to the application of the kit-recommended or NACB standard reference interval

Iodine status and its association with prevalence of thyroid diseases in adults from Jiangxi Province, China

BACKGROUND

Iodine is an essential element for the biosynthesis of thyroid-stimulating hormone (TSH). Both excessive and deficient iodine are major risk factors for thyroid diseases, including thyroid dysfunction, thyroid nodules, and thyroid autoimmunity (TAI). This study aimed to elucidate the relationship between iodine status and the prevalence of thyroid diseases through a national cross-sectional epidemiological survey in Jiangxi province (China).

METHODS

This population-based, cross-sectional study enrolled 2636 Chinese local inhabitants who aged over 18 years old from April to August in 2015. Physical examination was performed and biochemical indices, urinary iodine concentration (UIC), and TSH level were measured. The Chi-square test, nonparametric test, and 4 multivariate logistic regression models adjusted for risk factors were applied to analysis. Spearman correlation coefficients were calculated to investigate the relationship between iodine intake level and the prevalence of thyroid diseases.

RESULTS

The median UIC was 176.4 μg/L, and a significant difference was found in median UIC between men (182.45 μg/L) and women (169.25 μg/L) (P = 0.03). Among these study subjects, 14.4%, 44.5%, 26.1%, and 15.0% had deficient, adequate, more than adequate, and excessive iodine concentrations, respectively. The prevalence rates of hyperthyroidism, subclinical hyperthyroidism, hypothyroidism, subclinical hypothyroidism, thyroid nodules, and TAI were 0.91%, 0.57%, 0.34% and 7.89%, 9.45%, and 12.7%, respectively. Significant differences were found in iodine status, waist circumstance, systolic blood pressure (SBP), diastolic blood pressure (DBP), total cholesterol (TC), TSH, thyroid nodules, and TAI between men and women (P < 0.05). Compared with those with adequate UIC, subjects with excessive UIC had higher prevalence rates of thyroid dysfunction (odds ratio (OR) = 1.74, 95% confidence interval (CI): 1.40-2.54) and thyroid nodules (OR = 3.33, 95%CI 1.32-8.42). In addition, subjects with deficient and excessive UIC were at the higher risk of TAI compared with those with adequate UIC (OR = 1.68, 95%CI: 1.19-2.60; OR = 1.52, 95%CI: 1.04-2.96, respectively). UIC was positively correlated with the prevalence rates of thyroid nodules (r = -0.44, P < 0.01) and TAI (r = -0.055, P < 0.01). On the contrary, UIC was negatively correlated with the risk of thyroid dysfunction (r = -0.24, P > 0.05).

CONCLUSION

Adult inhabitants from Jiangxi province in the TIDE study were in the adequate iodine status. Excessive iodine status was noted as a risk factor for thyroid dysfunction and thyroid nodules. In addition, both iodine deficiency and excessive iodine were risk factors for TAI.

Effect of the transition from more than adequate iodine to adequate iodine on national changes in the prevalence of thyroid disorders: repeat national cross-sectional surveys in China

OBJECTIVE

Longitudinal studies have investigated the effects of changing iodine status on thyroid disorders, but the effect of a transition from more than adequate iodine to adequate iodine on national changes in prevalence adjusted for changing risk factors remains unclear.

DESIGN

Two repeat nationwide surveys were conducted from 2009-2010 to 2015-2017 to assess changes in thyroid disorder prevalence and iodine status in China.

METHODS

A multistage stratified random sampling method was used to obtain a nationally representative sample of urban adults aged 18 and older in mainland China in 2009 (n = 14 925) and 2015 (n = 12 553). Changes in thyroid disorder prevalence, urinary iodine concentration (UIC), and thyroid-stimulating hormone (TSH) levels were assessed. Logistic regression models were used to examine changes in prevalence over time.

RESULTS

The median UIC decreased significantly from 219.7 to 175.9 μg/L (P < 0.0001). The weighted prevalence of overt hyperthyroidism, subclinical hyperthyroidism, Graves' disease, and goitre decreased between 2009 and 2015 in the overall population (P < 0.05 for all). Despite no significant changes in subclinical hyperthyroidism or hypothyroidism or anti-thyroid peroxidase or anti-thyroglobulin antibody positivity prevalence, a significant increase in thyroid nodule prevalence (P < 0.0001) was found in the overall population. The 2.5th TSH percentile increased by 0.15 mIU/L (95% CI: 0.01 to 0.30 mIU/L, P = 0.04) from 2009 to 2015.

CONCLUSIONS

With the iodine status transition from more than adequate to adequate, thyroid disorder (except for thyroid nodules) prevalence remained stable or even decreased after adjusting for confounding factors among adults in mainland China between 2009 and 2015. Additional studies are needed to explore the reasons for the increased thyroid nodule prevalence.

Low Iodine Intake May Decrease Women's Fecundity: A Population-Based Cross-Sectional Study

Salt iodization is one of the most cost-effective strategies to eliminate iodine deficiency disorders (IDD). However, China’s dismantling of salt monopoly has reduced the availability of iodized salt in the susceptible population in pregnancy, which might cause IDD and have adverse health effects on both themselves and their offspring. The aim of our study was therefore to explore the association between IDD and women’s reproductive health. This is a population-based cross-sectional study conducted in 2018 in Zhejiang Province, China. A total of 1653 pregnant women participated in this study. Median urinary iodine concentration (UIC) in the population was used to assess iodine intake. Cox regression analyses were used to estimate the association between iodine intake and time to pregnancy, which was indicated with fecundability ratio (FR) and 95% confidence interval (CI). The percentage of participants with iodine deficiency who had been waiting longer than 13 months to get pregnant (20%; median UIC 119.6 μg/L) was significantly higher than those with iodine sufficiency (14%; median UIC 147.1 μg/L). A significant decrease in fecundity was observed in participants with iodine deficiency (FR, 0.820; 95% CI, 0.725−0.929) than those with iodine sufficiency. These findings indicate the importance of ongoing monitoring of iodine nutrition in women of reproductive age. Keeping a safe and optimal level of iodine nutrition during pregnancy should be emphasized.