Epigenetic effects of environmental pollutants may be related to carcinogenesis. This study aimed to explore the association between the global DNA methylation marker: 5-methyl-2-deoxycytidine (5mdC) and renal cell carcinoma (RCC), and further investigated whether plasma folate and vitamin B12 levels and 5mdC modified the association between blood cadmium concentrations and RCC. We recruited 174 RCC patients and 673 non-RCC controls. Blood cadmium concentrations, plasma folate and vitamin B12 levels were measured. The amount of 5mdC in the DNA sample was expressed as percentages of the total cytosine content. An increase of 5mdC (%) and plasma folate and vitamin B12 levels were associated with decreasing odds ratio (OR) of RCC. Although plasma folate levels were not directly associated with 5mdC (%), a combined effect was observed with the odds of low plasma folate levels and low 5mdC (%) were greater among RCC patients compared to controls (OR (95% confidence interval, CI) = 11.86 (5.27–26.65)). Additionally, we observed that the odds of low plasma folate and high blood cadmium levels were greater among RCC patients than in controls (OR (95% CI): 8.15 (1.39–7.13)). This study provides suggestive evidence that plasma folate levels may modify the associations between 5mdC (%) or blood cadmium concentrations and RCC.
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