Association of urinary iodine concentration with gestational diabetes mellitus in U.S. women: A NHANES cross-sectional study (2009–2016)

Epidemiological evidence on the association between urinary iodine concentration (UIC) and gestational diabetes mellitus (GDM) remains inconsistent. This study aimed to evaluate the relationship between UIC and GDM in U.S. women. We conducted a cross-sectional analysis using data from 1745 women aged ≥20 years in the 2009 to 2016 the National Health and Nutrition Examination Survey. UIC was measured via inductively coupled plasma dynamic reaction cell mass spectrometry, and GDM status was self-reported. All analyses incorporated the National Health and Nutrition Examination Survey weights, strata, and clusters to ensure national representativeness. Weighted multivariable logistic regression models were used to estimate odds ratios (ORs) and 95% confidence intervals (CIs). Model 1 was unadjusted; Model 2 adjusted for age, race, education, marital status, poverty-income ratio, body mass index, total cholesterol, and HbA1c; Model 3 further adjusted for alcohol intake, smoking, hypertension, hyperlipidemia, and prediabetes. Restricted cubic spline regression was applied to assess nonlinearity. Stratified and sensitivity analyses were performed to examine robustness. In fully adjusted weighted models, higher log-transformed UIC was associated with lower odds of GDM (OR = 0.69; 95% CI: 0.47-1.00). Compared with the lowest UIC quartile (Q1), adjusted ORs (95% CI) for GDM were: Q2: 0.48 (0.23-0.99), Q3: 0.43 (0.19-0.95), and Q4: 0.30 (0.13-0.73). The restricted cubic spline indicated a nonlinear inverse association (P for nonlinear = .009). Stronger inverse associations were observed among women with higher education, alcohol intake, and without hypertension or hyperlipidemia. Sensitivity analyses confirmed the robustness of the results. Higher UIC was independently associated with reduced GDM risk. However, due to the cross-sectional design and use of self-reported GDM, causality cannot be inferred and measurement bias may be present. Prospective studies using clinically validated GDM diagnoses and longitudinal iodine assessments are warranted.