Benefits of Magnesium
Monday 7 December 1998
Summary: A large 9 year study in the U.S. has suggested that a low magnesium level may be a risk factor for atherosclerosis, i.e. cholesterol damaged arteries and perhaps for abnormal blood clots too.
Norman Swan: Now I don't want to confuse you, but there's some interesting news about another element in our diet, another micronutrient, magnesium.
There have been suspicions around that magnesium might be essential for good heart function. In fact there's a controversy over whether magnesium should be given to people with acute heart attacks, but that's not what this story's about.
A large, nine year study of nearly 14,000 middle aged adults has suggested that a low magnesium level may be a risk factor for atherosclerosis, cholesterol damaged arteries, and perhaps for abnormal blood clots too.
One of the researchers is Dr Fred Brancati, who's at Johns Hopkins University in Baltimore.
Fred Brancati: We looked at two aspects of magnesium in the study. We looked at sero magnesium which doctors can get off of fairly routine blood tests, and we also looked at dietary magnesium intake, and part of the problem is that people with lower sero magnesiums, tend to be less healthy in a few different ways. For example people with diabetes tend to have lower magnesiums to start with. People who have high blood pressure and are on medications that induce frequent urination to lower the blood pressure, diuretic therapy, they tend to have lower seromagnesium levels, so part of the trick here -
Norman Swan: - is to separate cause from effect.
Fred Brancati: Exactly, and that's what we did and what we found was as we hypothesised, the risk of heart attacks over the subsequent five to seven years was indeed lower in the individuals who had higher serum magnesium.
Norman Swan: By how much?
Fred Brancati: By 45% lower in the women with the higher serum magnesiums, compared to their counterparts with the lower serum magnesiums.
Norman Swan: What about men?
Fred Brancati: Not as impressive, about 15% lower.
Norman Swan: But interestingly, you didn't really find a very strong association with magnesium intake, with the amount of magnesium people were eating in their diet.
Fred Brancati: Yes, and you know we got exactly the same sort of pattern in a parallel study we did looking at serum in dietary magnesium as predictors of the risk of adult onset diabetes, the same story where serum magnesium was associated but dietary magnesium not associated.
Norman Swan: You had a high serum magnesium, you had a lower risk of adult onset diabetes?
Fred Brancati: Exactly. Same sort of pattern. If anything, a little more impressive because we found the same sort of pattern in men and women, statistically significant. It was another piece of the puzzle for us, because one of the hypothesised connections between low magnesium and the risk of coronary heart disease, is that low magnesium might lead to the development of diabetes and resistance to the effects of insulin which may indicate a cascade of physiologic events leading to things like high blood pressure and abnormal cholesterol levels which could in turn lead to atherosclerosis, blockage of the arteries, and then ultimately to a heart attack. So that was one of the intermediate pieces of the puzzle we were trying to put together, and we got fairly consistent results.
But one bothersome fact you mention is this difference in the relationship between serum magnesium and risk versus dietary magnesium and risk. And there are a couple of possible explanations for that. One is purely methodologic, it's a lot easier to measure sero magnesium precisely with a blood test than it is to measure dietary magnesium intake over a period of a year or so, using even the most detailed questionnaires. So we think there's a lot more measurement error when we assess dietary magnesium.
Norman Swan: Which foods are you talking about here?
Fred Brancati: Fresh fruits and vegetables are high in magnesium. Some nuts are particularly high, green vegetables especially, soy beans and whole grains.
Norman Swan: What's the message then, from the study? Does it mean we go out and buy magnesium supplements, eat more fruit and vegetables which we knew already, or what?
Fred Brancati: Well the notion of eating more fruits and vegetables, right, we knew that already and we didn't need a study of magnesium to tell us to do that. I think one implication of the study is that we hope it spurs our scientific colleagues to look into this further.
Norman Swan: Is there evidence yet to say recommend to an Aboriginal community with a high risk of diabetes that they go on magnesium supplements?
Fred Brancati: Well now the supplement question is an interesting one. The quick answer is No, those data don't exist yet. But one of the possible explanations for this disparity in results between serum magnesium and dietary magnesium is that there are other determinants of serum magnesium of the body's internal set point that tend to override small differences that occur casually in dietary magnesium when it's not being intentionally manipulated. And it opens the door to the notion that well if one could overwhelm the internal set point by taking supplements, or by eating a diet that is specifically designed to be very high in magnesium, that might very well do the trick. In fact with regards to diabetes and glucose tolerance there are short term studies done on individuals who are hospitalised for a period of a week or two, that demonstrate very consistently that intravenous infusions of magnesiums or very high magnesium diets taken over a short run will improve the body's sensitivity to insulin and do provide a basis for that hypothesis, but the question of whether long term supplementation would be of benefit is an interesting and important one in an area where we're currently trying to mount randomised control trials to prove or disprove it.
Norman Swan: So perhaps wait a while before chewing the magnesium.
Dr Fred Brancati is Associate Professor of Medicine and Epidemiology at Johns Hopkins University in Baltimore.
Will have to give the biomagnesium a go.
