Magnesium levels don't predict heart risk

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NEW YORK: The hope that a simple blood test could help doctors identify patients likely to develop high blood pressure or heart disease is dashed by the findings of a new study published in the American Heart Association's American Heart Journal.

After analyzing data from more than 3,500 healthy people followed for as long as 20 years, a team of researchers concluded there is no association between blood magnesium levels and the probability of developing high blood pressure or heart disease in the future.

Researchers are always looking for good markers to identify people at risk of disease that might be forestalled with early intervention.

Magnesium is known to be important to the proper functioning of cells, and animal studies have found low blood levels of magnesium seem to raise blood pressure while higher magnesium intake wards off hardening of the arteries.

Because magnesium deficiency is common among women, the elderly and minorities and previous research in both animals and people has yielded mixed results, Dr. Thomas Wang at Massachusetts General Hospital in Boston, and colleagues looked for patterns in data gathered through the Framingham Heart Study.

In a population of 3,531 study participants who were healthy at the beginning of the study, 22 percent (551 cases) developed high blood pressure after 8 years, and 16 percent (554 cases) had a cardiovascular event such as heart attack or stroke within 20 years.

After analyzing the participants' blood magnesium levels at the beginning of the study and health outcomes after 8 and 20 years, the researchers concluded that within the normal range of blood magnesium in healthy people, there was no link between lower magnesium levels and future high blood pressure, heart disease, or death from any cause.

Because the study population was generally healthy, with blood magnesium levels in a fairly normal range between 1.15 and 2.46 milligrams per deciliter, the investigators caution that they could not assess the effects of extreme magnesium deficiency or abnormally high levels.

The finding "doesn't rule out importance of magnesium and doesn't say magnesium supplementation wouldn't be helpful, but it probably argues against routine checking of magnesium levels at least for the purpose of trying to find something you can intervene on to improve cardiovascular risks," Wang said.

Blood magnesium is just one of 20 or more measurements in an extended laboratory blood test that can run more than $100. Eliminating one element might not save much money, but knowing that it may not be as useful as once thought could influence a doctor's decision about which blood test to order - an "extended" version or a smaller "basic" test.

"As physicians consider how best to utilize resources especially to improve prevention, it probably is useful to know what are more informative and less informative blood tests," Wang said.

Wang is quick to point out that these study results do not address the value of measuring magnesium levels in hospitalized patients with heart disease.

"There is experimental and clinical data to suggest that low magnesium levels make a patient more susceptible to irregular heart rhythms, thus there's a reason to check magnesium levels in hospitalized patients after a heart attack," he said.

But for the population as a whole, "there is not a clear signal that routinely checking magnesium for the purpose of preventing cardiovascular disease is warranted," he said.