High levels of magnesium in the diet may lower a woman's risk of developing colon cancer. The findings from the study of U.S. women support the results of an earlier study of Swedish women. Still, the authors note that a clinical trial is needed to confirm that the benefit is due to magnesium intake rather than some related factor.

As reported in the American Journal of Epidemiology, Dr. Aaron R. Folsom and Dr. Ching-Ping Hong, from the University of Minnesota in Minneapolis, used food frequency questionnaires to assess magnesium intake in 35,196 Iowa women, between 55 and 69 years of age at baseline, who were followed for colorectal cancer from 1986 through 2002.

During follow-up, 1,112 women developed colorectal cancer, the report indicates. There was a nonsignificant trend toward decreased colorectal cancer risk as magnesium intake increased.

Further analysis showed that high magnesium intake offered no apparent protection against rectal cancer, but did significantly decrease the risk of colon cancer. Women in the highest quintile of intake were 23 percent less likely to develop colon cancer than their peers in the lowest quintile of magnesium intake.

In contrast, the Swedish study found that high magnesium intake was inversely associated with the risks of both colon and rectal cancer. The reasons for this difference are unclear, the authors note.

Magnesium has been hypothesized to cut the risk of colon cancer by reducing oxidative stress, improving insulin sensitivity, or through mechanisms that reduce proliferation of cells in the colon, the authors note.

SOURCE: American Journal of Epidemiology, February 2006.