Objectives: The association between dietary magnesium intake and the risk of colorectal cancer has been examined by many prospective studies, but remains controversial because of inconsistent results. We aimed to carry out a meta-analysis to investigate this.
Materials and methods: We assessed this association with categorical and dose–response meta-analysis of data from prospective cohort studies. Relevant studies were identified by searching MEDLINE, EMBASE, and OVID for studies published before 9 June 2012, with no restrictions. Relative risks (RRs) and 95% confidence intervals (CIs) for the highest versus lowest and dose–response association were estimated using random-effects models. Heterogeneity and publication bias was investigated, and subgroup, sensitivity, and meta-regression analyses were carried out.
Results: The analysis included 333 510 participants with 7435 colorectal cancers from seven prospective cohort studies. The summary RR for the highest versus the lowest intake of dietary magnesium was 0.81 (95% CI: 0.70–0.92) for colorectal cancer, 0.76 (95% CI: 0.64–0.88) for colon cancer, and 0.82 (95% CI: 0.58–1.06) for rectal cancer. For men and women, the pooled RR was 0.76 (95% CI: 0.51–1.01) and 0.81 (95% CI: 0.68–0.94), respectively. Significant inverse associations of colorectal cancer and dietary magnesium emerged in nonlinear models (p nonlinearity=0.03). The greatest risk reduction was observed when dietary magnesium intake increased from very low levels.
Conclusion: Dietary magnesium intake has a statistically significant nonlinear inverse association with the risk of colorectal cancer. The greatest reduction for magnesium intake is 200–270 mg/day. Whether the association is causal or because of confounding warrants further investigation.