At least three cohort studies have been published relating to the possible role of magnesium in reducing risk of colorectal cancer in women.
The first was prospective study from Sweden and reported in JAMA in which researchers found a reduced occurrence of colorectal cancer in women who had a higher dietary intake of magnesium (1).
Hanging on the coat-tails of the Swedish study, U.S. researchers assessed magnesium status of a cohort in Iowa women and found the similar results of reduced risk (2).
The latest was from the Netherlands, which found a few differences from the first two, indicating that there was no significant trend of lowering risk of colorectal cancer except in populations of overweight subjects (3).
According to the latest study, the method by which magnesium has a protective effect is thought to be through decrease of insulin resistance (3). However, as suggested by the U.S. researchers, more observational studies are necessary and, perhaps, clinical trials to assess whether or not the results can be attributed to magnesium or other factors in relation to a high-magnesium diet (2).
Could fiber in green leafy vegetables be a variable? I imagine so.
1. Larsson SC, Bergkvist L, Wolk A. Magnesium intake in relation to risk of colorectal cancer in women. JAMA 2005;293:86-9.
2. Folsom AR, Hong CP. Magnesium intake and reduced risk of colon cancer in a prospective study of women. Am J Epidemiol 2006;163:232-5.
3. van den Brandt PA, Smits KM, Goldbohm RA, Weijenberg MP. Magnesium intake and colorectal cancer risk in the Netherlands Cohort Study. Br J Cancer 2007;96:510-3.