Environmental exposure to cadmium and risk of thyroid cancer from National Industrial Complexes: a population-based cohort study

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BackgroundCadmium is known to act as a thyroid disruptor and carcinogen in human. Recent evidence suggests cadmium may play a role in thyroid cancer because of its estrogenic activity, but the role of cadmium as a human thyroid carcinogen is still unclear. Our aim was to investigate the association between urinary cadmium and primary thyroid cancer in a prospective design and the modifying effect of hypertension on this association. Methods This study was conducted to collect and analyze the pollutant data comprehensively collected from eight National Industrial Complexes areas including Ulsan, Pohang, Gwangyang, Yeosu, Chungju, Gangneung, Cheongju and Daesan from 2003 to 2010. We included 4195 participants aged over 19 years with measured urinary cadmium for analysis. Urine samples collected at enrollment into the cohort were analyzed for cadmium and creatinine. Incident thyroid cancer patients were identified in the Korea Central Cancer Registry. We estimated incidence rate ratios (IRRs) for thyroid cancer in Cox proportional hazards models with random effects, using follow-up time as time scale and calculated 95% confidence intervals (CIs). In addition, we conducted stratified analysis by hypertension. Results Higher urinary cadmium was associated with increased risk for thyroid cancer (HRTertile 3 vs Tertile 1 1.44, 95% CI = 1.03 to 5.14, P trend < 0.001; HR2.7-fold increase 1.47, 95% CI = 1.02 to 2.11 per mg/g). After stratification by hypertension, there was a positive association between urine cadmium and thyroid cancer in participants with hypertension (HR = 5.37, 95% CI = 1.13 to 25.64 per mg/g) but not in participants without hypertension (p for interaction 0.03). Conclusion This prospective study showed positive association between urinary concentration of cadmium and risk for development of thyroid cancer. The results also show that hypertensive patients are particularly vulnerable to the effects of cadmium exposure.