The association between deficient manganese levels and breast cancer: a meta-analysis

There are conflicting reports on the correlation between manganese (Mn) levels and breast cancer. The purpose of the present study is to clarify the association between Mn levels and breast cancer using a meta-analysis approach. We searched articles indexed in Pubmed and the Chinese Journal Full-text Database (CJFD) published as of August 2014 that met our predefined criteria. Eleven eligible studies involving 1302 subjects were identified. Overall, pooled analysis indicated that subjects with breast cancer had lower Mn levels than the healthy controls (SMD = -1.51, 95% CI = [-2.47, -0.56]). Further subgroup analysis found a similar pattern in China (SMD = -1.32, 95% CI = [-2.33, -0.32]) and Korea (SMD = -4.08, 95% CI = [-4.63, -3.54]), but not in Turkey (SMD = -0.96, 95% CI = [-3.19, 1.27]). Further subgroup analysis also found a similar pattern in different sample specimens (serum: SMD = -1.24, 95% CI = [-2.31, -0.16]; hair: SMD = -1.99, 95% CI = [-3.91, -0.06]) and different types of Mn measurement (inductively coupled plasma-atomic absorption spectrometry (ICP-AAS): SMD = -1.14, 95% CI = [-2.24, -0.04]; graphite furnace atomic absorption spectroscopy (GFAAS): SMD = -1.94, 95% CI = [-2.38, -1.49]; inductively coupled plasma-atomic emission spectrometry (ICP-AES): SMD = -3.77, 95% CI = [-4.70, -2.85]). No evidence of publication bias was observed. In conclusion, this meta-analysis supports a significant association between deficient Mn levels and breast cancer. However, the subgroup analysis found that there was contradiction regarding races and geography, like China and Turkey. Thus this finding needs further confirmation by trans-regional multicenter, long-term observation in a cohort design to obtain better understanding of causal relationships between Mn levels and breast cancer, through measuring Mn at baseline to investigate whether the highest Mn category versus lowest was associated with breast cancer risk.