The association between dietary intake of iodine and kidney stones: A study of the National Health and Nutrition Examination Survey 2007-2018.

It is still not clear what the relationship is between dietary iodine intake and kidney stones. The purpose of this study was to examine the link between iodine intake and kidney stone risk in people aged 20 to 60 years. Data from the National Health and Nutrition Examination Survey (2007-2018) were analyzed, including 9443 participants aged 20 to 60 years. Urinary iodine concentration (UIC) was used to assess iodine status. Based on urinary iodine concentration quartiles, participants were classified into 4 groups (Q1: <67.7 μg/L, Q2: 67.7-121.2 μg/L, Q3: 121.2-215.5 μg/L, Q4: ≥215.5 μg/L). Multiple logistic regression analysis adjusted for covariates was employed to investigate the link between urinary iodine concentration and kidney stones. We used trend analysis and restricted cubic spline (RCS) curves to analyze the linear correlation. Within the study population, kidney stones had a prevalence of 7.60% (718 cases). The average level of urinary iodine concentration was 262.69 μg/L. The multivariable analysis showed that Q2 (urinary iodine concentration: 67.7-121.2 μg/L) had a notably higher risk of kidney stones compared to Q1 (urinary iodine concentration: <67.7 μg/L; model 3: OR = 1.47, 95% CI: 1.05-2.06), while Q3 (urinary iodine concentration: 121.2-215.5 μg/L) and Q4 (urinary iodine concentration: ≥215.5 μg/L) showed no statistically significant associations. Trend analysis indicated no linear relationship between urinary iodine concentration and kidney stone risk (P > .05). The restricted cubic spline curves indicated a nonlinear trend, and the inflection point corresponded to a UIC of 134.9 μg/L. Sensitivity analysis further confirmed the reliability of the conclusion. Our findings suggest that a urine iodine level ranging from 67.7 to 121.2 μg/L may be associated with kidney stones, and the association appears nonlinear. Further investigations are warranted to clarify the causal relationships and mechanisms underlying iodine and nephrolithiasis.