Another Benefit of Magnesium?

Summarized by Robert W. Griffith, MD
March 24, 2005

Introduction

Recently we reported a study showing that magnesium in the diet may help prevent type 2 diabetes (see first link below). Now there's news that magnesium may also reduce the risk of colon cancer. Maybe it's time we paid more attention to this mineral; it's known to have a crucial role in cell reproduction. Researchers in Sweden examined dietary information from a large group of women attending a mammography clinic, and published their findings in the Journal of the American Medical Association.

What was done

The participants were part of the Swedish Mammography Cohort, which was established in 1987-1990. All women between 40 and 75 living in two counties in central Sweden were mailed a questionnaire about their diet, along with information on their weight, height, and educational level. Over 66,500 women replied, representing three-quarters of the available population. A second questionnaire was sent 10 years later, which included additional questions about a family history of colon cancer, smoking habits, physical activity, and multivitamin or aspirin intake.

Specific contents of the diet were calculated based on the reported food frequency questionnaires. Women with a previously reported cancer were excluded. This left over 61,000 women who were followed-up until a diagnosis of colorectal cancer, death, or June 2004 occurred. Diagnoses of cancer were confirmed through the Swedish Cancer Registry System.

The women were classified into five groups (called quintiles), according to the level of magnesium they consumed. This allowed comparison of the frequency of colorectal cancer in the groups with different amounts of dietary magnesium.

What the study showed

The average age of the women was 54, and their average body mass index (BMI) was 24.7 (i.e. normal). The average length of follow-up was 14.8 years.

The established quintiles were daily magnesium intakes of below 209, 209-224, 225-237, 238-254, and 255 mg or above. In general, women in the higher magnesium quintiles had a lower calorie intake, less saturated fat, more fiber, and consumed more calcium, zinc, beta-carotene, folate, and vitamin B6, compared to the lowest-magnesium quintile.

There were 805 women diagnosed with colorectal cancer during the study period - 547 colon cancers, 252 rectal cancers, and 6 with both types.

Adjustments were made for age, BMI, educational level, calorie intake, saturated fat, fiber, and the other factors mentioned above. This allowed the true 'relative risk' or likelihood of colorectal cancer to be calculated for the 4 higher quintiles, compared to the lowest magnesium-intake quintile.

The risk of colorectal cancer was directly related to the magnesium intake - the higher the intake, the lower the risk. Those women in the highest magnesium intake quintile were only 60% as likely to develop colorectal cancer as those in the lowest magnesium intake quintile. The findings were similar for both colon cancers and rectal cancers.

What these results mean

This is the first large study to demonstrate an association between magnesium intake and colorectal cancer in humans. It shows that a high magnesium intake can almost cut the risk of colorectal cancer in half, compared with a low magnesium diet. And remember that the foods that provide magnesium include fruits and vegetables, whole grain foods, and beans - all things that are good for you in other ways, as well. If you follow a sensible diet, there's no need for any magnesium supplements.

Source

• Magnesium intake in relation to risk of colorectal cancer in women. SC. Larsson, L. Bergkvist, A. Wolk, JAMA, 2005, vol. 293, pp. 86--89

Related Links
Eat More Magnesium to Avoid Diabetes?
University of Pittsburgh: Magnesium
Nutrition in the Elderly