Toenail zinc and risk of prostate cancer in the MCC-Spain case-control study

Background: Some researchers have suggested that zinc (Zn) could reduce the risk of prostate cancer (PC). However, research from observational studies on the relationship between PC risk and biomarkers of Zn exposure shows conflicting results. Objectives: To evaluate the association between toenail Zn and PC, considering tumour extension and aggressiveness, along with a gene-environment approach, exploring the interaction of individual genetic susceptibility to PC in the relationship between toenail Zn and PC. Methods: In MCC-Spain study we invited all incident PC cases diagnosed in the study period (2008-2013) and recruited randomly selected general population controls. In this report we included 913 cases and 1198 controls with toenail Zn determined by inductively coupled plasma mass spectrometry. To measure individual genetic susceptibility, we constructed a polygenic risk score based on known PC-related single nucleotide polymorphisms. The association between toenail Zn and PC was explored with mixed logistic and multinomial regression models. Results: Men with higher toenail Zn had higher risk of PC (OR quartile 4 vs.1: 1.41; 95% CI: 1.07-1.85). This association was slightly higher in high-grade PC [(ISUP <= 2 Relative risk ratio (RRR) quartile 4 vs.1: 1.36; 1.01-1.83) vs. (ISUP3-5 RRR quartile 4 vs.1: 1.64; 1.06-2.54)] and in advanced tumours [(cT1-cT2a RRR quartile 4 vs.1: 1.40; 95% CI: 1.05-1.89) vs. (cT2b-cT4 RRR quartile 4 vs.1: 1.59; 1.00-2.53)]. Men with lower genetic susceptibility to PC were those at higher risk of PC associated with high toenail Zn (OR quartile 4 vs.1: 2.18; 95% CI: 1.08-4.40). Discussion: High toenail Zn levels were related to a higher risk for PC, especially for more aggressive or advanced tumours. This effect was stronger among men with a lower genetic susceptibility to PC.