A relatively high intake of magnesium appears to protect against bowel cancer. This finding gives insight into how diet accounts for about one third of our risk of cancer.
Ellen Kampman, professor of Nutrition and Cancer, studied a large group of bowel patients in collaboration with some London counterparts. The results were published at the beginning of August on the website of the American Journal of Clinical Nutrition.
Among the participants who consumed relatively large amounts of magnesium, pre-cancerous symptoms were detected less frequently during the study. It appears that the risk goes down by about 10 percent for every additional 100 milligrams of magnesium consumed. In order to check their own results, the team analysed afresh all the old data from comparable epidemiological studies. Their conclusions were supported by these data. It is striking that the link is only significant among the over 55 age group and the overweight. Kampman: 'I don't have a good explanation of that yet.'
The result has no consequences for nutritional guidelines because indirectly the standard advice already covers an adequate intake of magnesium. 'We already tell people they should eat more dairy produce, vegetables and high-fibre products to prevent bowel cancer', says Kampman. 'There is a lot of magnesium in those foods too and that message will not change now. I still would not recommend magnesium supplements because it is not clear what effect a high intake of magnesium would have.' RR
The subjects of this study were about 1450 people undergoing a colonoscopy because of bowel complaints. The participants filled in a questionnaire with 178 foodstuffs and said how often they ate them. Using average magnesium contents for these foods, the researchers calculated the magnesium levels these eating habits gave them. Then the researchers compared the group that was free of polyps with those found to have a (benign) tumour. These data were corrected for factors such as smoking habits, diabetes, BMI and physical exercise.
There were already indications that magnesium had an influence on the development of bowel cancer but the evidence was never conclusive. 'After this study I have a very strong hunch that there is a link', says Kampman. 'It was certainly unexpected that we mainly saw a link with advanced adenomas. We thought we were more likely to see something in the early stages. Kampman speculates that magnesium does not play a role in the formation of benign polyps, but precisely in the progression to becoming more serious tumours. 'You have to reckon on 20 to 30 percent of people over 50 having polyps. Luckily they do not all go on growing.' The question remains which ones do and which ones do not.