Context: Magnesium is an essential nutrient for humans because it is required for the maintenance of genomic stability. Genetic instability is strongly implicated in cancer risk. However, the associations between dietary magnesium intake and cancer risk has not been evaluated in detail. Objective: The objective of this study was to examine the relationship of dietary magnesium intake and DNA repair capacity (DRC) on lung cancer risk. Methods: We used an ongoing study of 1,676 incident lung cancer patients and 1,676 matched healthy controls to achieve our objective. A modified NCI-Block FFQ and a lifestyle questionnaire were interviewer-administered to each participant. Cellular DRC was assessed by the host-cell reactivation assay that measures nucleotide-excision repair capacity in peripheral blood lymphocytes culture. Multiple logistic regression analysis was used to assess the associations between dietary magnesium and DRC with lung cancer risk. Results: After adjustment for recognized confounding factors, the odds ratios (OR) and 95% confidence intervals (CI) of lung cancer by increasing quartiles of dietary magnesium intake were: 1.0, 1.07 (0.82-1.38), 0.89 (0.67-1.18), 0.67 (0.48-0.94), respectively (P-trend<0.0001). For men, the OR and 95% CI by increasing quartile of magnesium intake were: 1.0, 1.07 (0.74-1.55), 0.74 (0.50-1.09), 0.56 (0.36-0.86), respectively (P-trend=0.01). In women, we did not observe a significant trend. We also found a significant (P<0.001) interaction with magnesium intake and DRC in these multivariate models. In both cases and controls, there was a trend for increasing DRC with increasing quartile of magnesium intake, although the trends were only borderline statistically significant (P=0.09). In stratified analysis, using those with high dietary magnesium and proficient DRC as the referent group, the ORs were: 1.0, 1.37 (1.02-1.83) for high dietary magnesium and suboptimal DRC, 1.55 (1.16-2.06) for low dietary magnesium and proficient DRC, and 2.30 (1.74-3.04) for low dietary magnesium and suboptimal DRC, respectively (P-trend<0.0001). Conclusions: Our results suggest that dietary magnesium intake is inversely associated with risk of lung cancer, and there may be joint effects between magnesium intake and DRC on lung cancer risk. Given the known limitations of case-control studies and dietary assessments, these findings need to be confirmed in future investigations.

[Fifth AACR International Conference on Frontiers in Cancer Prevention Research, Nov 12-15, 2006]