Null Results in Brief Total Magnesium Intake and Colorectal Cancer Incidence in Women

Magnesium is an essential ion that has an important role in regulating cell cycles and maintaining genomic stability (1). Administration of supplemental magnesium in animals with experimentally induced colon cancer resulted in fewer colon tumors and smaller cryptal cells of the colon (2), suggesting an inhibitory role of magnesium in colon cancer cell proliferation. The mechanism by which magnesium prevents the growth of colon tumors was later found to be due to the inhibition of c-myc oncogene expression in the colon cancer cells (3) and the potentially reduced toxic effects of bile acids on colonic epithelial cells (4). At the intracellular level, magnesium also effectively modulates insulin activity (5, 6). Magnesium deficiency is often seen among patients with insulin resistance and type 2 diabetes (5, 6), which have also been linked to an increase in colorectal cancer incidence (7-9). Observational studies of the association between magnesium intake and colorectal cancer incidence are very sparse. A case-control study found that magnesium level in drinking water was not associated with death from cancers of the colon (10) and rectum (11). On the basis of a dietary questionnaire, however, two recent prospective studies observed an inverse association between total magnesium intake and incident colorectal cancer (12, 13), although one study reported that the inverse association was only limited to colon cancer (13). Because more data are needed to confirm the association, we prospectively evaluated the association between total magnesium intake and colorectal cancer incidence in middle-aged and older women in the Women’s Health Study.