A recent prospective study among Swedish women suggested an inverse association of dietary magnesium intake with incidence of colorectal cancer. The authors assessed this association in a cohort of 35,196 Iowa women initially free of cancer and aged 55–69 years in 1986. Intakes of magnesium and other nutrients were assessed by food frequency questionnaire at baseline. Over 17 years of follow-up through 2002, 1,112 women developed colorectal cancer.
After adjustment for age, energy, other nutrients, and risk factors for colorectal cancer, the hazard ratios of colorectal cancer across quintiles of magnesium intake were 1.00, 0.96, 0.83, 0.87, and 0.80 (95% confidence interval: 0.62, 1.03; ptrend = 0.06). The association was largely absent for rectal cancer but, for colon cancer, the hazard ratios were 1.00, 1.00, 0.88, 0.85, and 0.77 (95% confidence interval: 0.58, 1.03; ptrend = 0.04). These findings offer further evidence that a diet high in magnesium may reduce the occurrence of colon cancer among women. If replicated by other observational studies, a clinical trial would be needed to determine whether it is magnesium, specifically, and not other aspects of the contributing foods, that may offer benefit.