Animal studies have suggested that the mineral could play a role in the prevention of the cancer but there has been little data in humans.
Using a population-based prospective cohort of 61,433 women, researchers at the Karolinska Institute found that women with the highest intakes of the mineral had a 40 per cent lower risk of developing the disease than those with the lowest intakes.
"This population-based prospective study suggests that a high magnesium intake may reduce the occurrence of colorectal cancer in women," conclude Susanna Larsson and colleagues in the 5 January issue of the Journal of the American Medical Association (293, pp86-89).
The findings are significant as researchers have recently identified a deficiency of the mineral in European populations.
Writing in a special supplement on magnesium in the December 2004 issue of the Journal of the American College of Nutrition (vol 23, no 6, 704S-711S), Dr Jean Durlach from the International Society for the Development of Research on Magnesium at the Pierre et Marie Curie University in Paris said that about 20 per cent of the French population consumes less than two-thirds of the RDA for magnesium, with women in particular having low intakes.
Approximately 150,000 people in the US are diagnosed with colorectal cancer each year. The cancer is the second leading cause of cancer death, and the risk of contracting it increases with age.
Calcium has also been shown to lower risk of developing the disease although researchers are still unsure how this benefit is produced.