Study on the Relationship Between Serum Iodine and Thyroid Dysfunctions: a Cross-Sectional Study

The relationship between serum iodine (SIC) and thyroid dysfunctions in adults is poorly understood, and this study aimed to explore their relationship. A total of 1320 participants were included in the final analysis. We collected basic demographic information, blood, and spot urine samples to determine serological indices and iodine nutritional status. The median (IQR) of urinary iodine (UIC)/urinary creatinine (UCr), UIC, SIC were 138.1 (91.1, 207.6) mu g/g, 155.8 (94.5, 211.1) mu g/L, and 70.6 (59.8, 83.9) mu g/L, respectively. The 90% reference ranges for UIC/UCr and SIC were 66.5-349.8 mg/g and 49.3-97.1 mu g/L. SIC was positively correlated with UIC and UIC/UCr. The prevalence of overt hypothyroidism and subclinical hypothyroidism in female was significantly higher than that in male (P = 0.02, P = 0.002). In male, subjects above the upper reference value of SIC (97.1 mu g/L) had a higher risk of subclinical hyperthyroidism (OR = 4.46, 95% CI: 1.29, 12.8) and overt hypothyroidism (OR = 5.59, 95% CI: 1.88, 6.42). In female, subjects below the lower reference value of SIC (49.3 mu g/L) had a higher risk of overt hypothyroidism (OR = 2.18, 95% CI: 1.10, 4.06), TgAb positive (OR = 1.97, 95% CI: 1.15, 3.32) and TPOAb positive (OR = 2.48, 95% CI: 1.41, 4.26). In conclusion, serum iodine can be used as an indicator to evaluate iodine nutritional status and thyroid dysfunctions. Higher serum iodine concentration was associated with an increased risk of subclinical hyperthyroidism and overt hypothyroidism in men; lower serum iodine concentration was associated with an increased risk of overt hypothyroidism and positive TgAb and TPOAb in women.