Characteristics of Salivary Iodine Concentration in Elderly Residents of High-iodine Areas.

Salivary iodine is considered a potential indicator for assessing iodine nutrition status. However, there is currently a lack of research data on the characteristics of salivary iodine concentration (SIC) in the elderly population. To evaluate the characteristics of SIC and assess its efficacy in diagnosing thyroid disorders among the elderly population, a cross-sectional study was conducted in a high-iodine area. Spot urine, 24-h urine, saliva, drinking, and cooking water samples were collected from the elderly participants. Iodine concentrations were measured in all these samples. Fasting venous blood samples were obtained to assess thyroid function. The study included 1387 elderly individuals from urban (n = 707) and rural (n = 680) areas. Rural residents showed significantly higher median concentration of cooking water iodine (CWIC) and SIC compared to urban residents (P < 0.001). The median SIC in rural elderly was 2733.3 μg/L versus 860.4 μg/L in urban elderly. SIC demonstrated a significant positive correlation with age (P < 0.001). Multiple linear regression analysis revealed significant positive associations between SIC and drinking water iodine concentration (β = 0.341, 95% CI 0.312-0.370), CWIC (β = 0.393, 95% CI 0.356-0.431), thyroid dysfunction (β = 0.107, 95% CI 0.050-0.164), and goiter (β = 0.236, 95% CI 0.129-0.342). Logistic regression showed that higher SIC levels were associated with increased risk of thyroid dysfunction, with odds ratios ranging from 1.649 to 1.994 for ascending SIC categories. The elderly residents in high-iodine areas, particularly in rural settings, exhibit elevated salivary iodine concentrations that increase with age. These high-iodine levels are significantly associated with an increased risk of thyroid dysfunction.