Serum and Hair Nickel Levels and Breast Cancer: Systematic Review and Meta-Analysis

Several studies have investigated the relationship between serum and hair nickel (Ni) concentration and breast cancer, but the results were inconsistent. Thus, we conducted a systematic review and meta-analysis to evaluate the association between serum and hair nickel levels and breast cancer. Nine studies determining the serum nickel levels and six studies evaluating the hair nickel levels were identified in a systematic search of PubMed, China Knowledge Resource Integrated Database, Wanfang, and China Biomedical Literature Service System databases. Based on a random-effects model, standard mean differences (SMD) and the corresponding 95% confidence intervals (CI) were pooled to compare the nickel levels between different groups. Compared with healthy controls, the serum nickel levels in breast cancer were significantly higher (SMD (95% CI) 1.76 (0.82, 2.70)), as well as in those post-treated cases (SMD (95% CI) 2.56 (1.18, 3.94)). For breast cancer cases, the treatment made no significant decrease in serum nickel levels (SMD (95% CI) −0.29 (−1.17, 0.59)). In hair, the nickel levels in breast cancer were slightly higher than in controls, but not significant (SMD (95% CI) 0.16 (−1.08, 1.40)). In conclusion, high serum nickel levels were associated with breast cancer, and nickel exposure might be a risk factor for breast cancer.