Relationship between internal metal exposure and thyroid cancer incidence: a case-control study simultaneously validated by BKMR and WQS models.

The global incidence of thyroid cancer is increasing, attracting great attention. Heavy metals affect human health and cause different diseases through various mechanisms. Several studies have identified heavy metals as risk factors for thyroid cancer and examined the association between heavy metals and the development of thyroid cancer. However, the mixed effects of multiple heavy metals on thyroid cancer are still unknown. In this study, twelve heavy metals including iron (Fe), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), selenium (Se), strontium (Sr), cadmium (Cd), cesium (Cs), palladium (Ba), mercury (Hg), and lead (Pb), in urine from thyroid cancer patients and healthy adults, were measured. The results revealed that the levels of Fe, Ni, and Cu were significantly higher in the case group than in the control group. Weighted quantile sum (WQS) and Bayesian kernel-machine regression (BKMR) analyses consistently showed that heavy metal mixtures in urine were positively associated with the risk of thyroid cancer, with metals such as Fe and Ni being the main contributors. Further epidemiological surveys are needed in the future to investigate the effects of individual or multiple heavy metals on thyroid disease.