Association between urinary iodine concentration and the risk of papillary thyroid cancer by sex and age: a case-control study.

Previous studies on dietary iodine intake and the risk of papillary thyroid cancer (PTC) have demonstrated inconsistent results. We aimed to evaluate the association between urinary iodine concentration (UIC), a surrogate biomarker for dietary iodine intake, and the risk of thyroid cancer stratified by sex and age in an iodine-sufficient area. A hospital-based case-control study was conducted in Seoul, South Korea. A total of 492 cases of newly diagnosed PTC and 595 controls were included. Compared with the lowest quartile of creatine-adjusted UIC (< 159.3 μg/gCr), the highest quartile (≥ 1037.3 μg/gCr) showed an increased risk of PTC (odds ratio [OR] 1.49, 95% confidence interval [CI] 1.04-2.13), especially in those who were < 45 years old (p = 0.01) compared with those who were ≥ 45 years old (p = 0.48). For those who were < 45 years old, a positive association between creatinine-adjusted UIC and the risk of PTC was observed in both men (q4 vs. q1, OR 4.27, 95% CI 1.14-18.08) and women (OR 1.97, 95% CI 1.04-3.78). For those who were ≥ 45 years old, no association was found in any sex. Creatinine-adjusted UIC was positively associated with the risk of PTC, especially in those who were younger than 45 years for both men and women.