Copper and Melanoma Risk: Results from NHANES 2007–2018 and Mendelian Randomization Analyses

Copper is an essential trace element obtained from food. There is a paucity of observational or prospective studies that have investigated the relationship between copper and melanoma risk. Copper serves as a cofactor for pivotal enzymes involved in mitochondrial respiration, antioxidant defense, and neurotransmitter synthesis. Undoubtedly, copper plays an indispensable role in the initiation and progression of tumors, particularly melanoma; however, further investigations are warranted to elucidate the underlying mechanisms linking copper and melanoma risk. Given the availability of dietary copper and serum copper data in the NHANES database, we conducted an investigation into the association between dietary copper intake and serum copper levels with melanoma risk. We enrolled 26,401 individuals with dietary copper data in the 2007–2018 NHANES database. To mitigate confounding variables, a propensity score matching (PSM) was performed. To assess the association between dietary copper intake and melanoma risk, we employed a multivariate logistic regression analysis before and after PSM. The restricted cubic spline analysis was utilized to determine whether there is a non-linear relationship between dietary copper intake and melanoma risk, with subgroup analysis conducted to determine beneficiaries. Then, those with blood copper data from the enrolled population with dietary copper intake were screened out, and subsequently, multivariate logistic regression models were subsequently constructed to investigate the association between serum copper levels and melanoma risk after PSM. Mendelian analysis was further utilized to validate the results of the NHANES database using serum copper as the exposure factor and melanoma as the outcome variable. The study found that melanoma risk was associated with dietary copper intake before and after PSM, demonstrated by multiple logistic regression. The relationship between dietary copper intake and melanoma risk was non-linear, with a reduced risk observed above approximately 2.5 mg/day, as shown by the RCS. The evidence suggests that an increased intake of copper is linked to a decreased risk of melanoma. To clarify the mechanism behind the increased risk of melanoma due to higher dietary copper intake, we analyzed the population data from the NHANES database on serum copper and dietary copper intake. Our results indicated that there is no causal relationship between serum copper and melanoma risk. Mendelian randomization analysis of multi-database data sources confirmed the conclusion of the NHANES database analysis. Dietary copper is a protective factor against melanoma, and serum copper or blood copper is not associated with melanoma risk. This suggests that serum or blood copper is not responsible for the protective effect of dietary copper intake on melanoma risk, and the mechanisms need to be further investigated.