Association of Urinary Iodine Concentration With Cognitive Function Among Older Adults: NHANES 2011-2014

The purpose of this study is to investigate the relationship between urinary iodine concentrations (UIC) and cognitive function among elderly individuals in certain regions of the United States, addressing a significant gap in the existing literature regarding urinary iodine and cognitive decline in older populations. UIC and cognitive function assessments of participants in the National Health and Nutrition Examination Survey were selected for the 2011-2014 cycle. Cognitive function assessments included: (1) a word learning and recall module from the Coalition to Establish a Registry for Alzheimer's Disease (CERAD); (2) an animal fluency test; and (3) the Digit Symbol Substitution Test (DSST). Based on the average z-scores of three cognitive tests, participants were classified into low cognitive status and normal cognitive status, with those in the lowest 25th percentile of average z-scores categorized as having low cognitive performance. Iodine deficiency (UIC < 100 μg/L) was associated with a significantly reduced risk of cognitive decline compared to the adequate iodine intake group (UIC 100-199 μg/L) (adjusted OR = 0.54, 95% CI: 0.29-0.99; p = 0.046). No significant differences in risk were observed for above requirement (UIC 200-299 μg/L) or excessive iodine intake (UIC ≥ 300 μg/L). This cross-sectional study provides the first evidence linking UIC to cognitive outcomes in older adults. Contrary to expectations, participants with iodine deficiency demonstrated significantly lower risk of cognitive decline compared to those with adequate iodine intake.