Effects of long-term excessive iodine intake on blood lipids in Chinese adults: a cross-sectional study

Objective: The aim of this study was to evaluate the effects of long-term excessive iodine intake on blood lipids in adults. Methods: Three counties from Dezhou city and Liaocheng city in the Shandong province of China were selected as survey locations. Three to five villages were selected from each county and then categorized by the iodine concentration detected in the groundwater into Low (<10 µg/L), Medium (10–150 µg/L), High (150–300 µg/L), and Excessive (>300 µg/L) groups. A self-reported questionnaire was completed by each subject to provide demographic characteristics. Body height, weight, and blood pressure were recorded by trained staff. Blood lipids were measured. Results: A total of 2156 subjects were recruited for the final analysis. The serum triglyceride (TRIG) was significantly higher in the Excessive group than in the other three groups (P< 0.05). Total cholesterol (TCHOL) and low-density lipoprotein-cholesterol (LDL-C) showed downward trends with the increases in the water iodine concentration. A statistical significance of the crude correlation coefficient was detected between the water iodine concentration and the TRIG, TCHOL, or LDL-C (P< 0.05). A significant correlation was also noted between the water iodine concentration and TCHOL or LDL-C after adjustment for covariates. High iodine concentration was a significant protective factor for TCHOL and LDL-C in adults, whereas elevated BMI and advancing age were risk factors for both variables. Conclusion: An association was identified between iodine excess and low TCHOL or LDL-C. In areas with excessive iodine, iodine intake should be considered in studies examining the factors that influence blood lipids.