That zippy little Mg

Low serum magnesium is associated with
higher risk of stroke in patients with blocked arteries.
But are supplements the answer?

By Maria Turner

Low serum magnesium (Mg) levels are associated with an increased risk of adverse neurological events, including ischemic stroke and carotid revascularization, in patients with advanced atherosclerosis, according to a study published in the January issue of Stroke.

Mg is a natural calcium antagonist that is thought to play an important role in the vascular system. Serum Mg levels are indicative of levels of intracellular free Mg, the physiologically active form of the element, and are therefore used for assessing Mg disorders. Previous studies have shown depressed serum Mg levels in patients with vascular disease and the Atherosclerosis Risk in Communities Study demonstrated an inverse relationship between serum Mg and carotid atherosclerosis in healthy adults.

The Stroke study involved 323 patients, 197 men and 126 women with a median age of 68 who had been admitted to hospital with symptomatic peripheral artery disease (PAD) (atherosclerosis affecting the extremities) and intermittent claudication (leg pain, most often in the calves, resulting from blocked arteries in the leg). The patients were followed for an average of 20 months for occurrence of ischemic stroke, stenting and carotid endarterectomy (surgical removal of deposits in the walls of the carotid artery).

After adjusting for comorbidities and other cardiac risk factors such as diabetes mellitus, smoking, history of myocardial infarction and stroke, and use of diuretics and statins, researchers found that patients in the lowest third for serum Mg levels showed a threefold increase in risk of neurological events compared to patients in the middle and highest thirds. There was no association between serum Mg levels and coronary events or all-cause mortality.

The study authors admitted that there are several limitations to the study, including a lack of data on the dietary intake of Mg of the study population and on other drugs that may influence serum Mg levels, such as biophosphonates and nonsteroidal anti-inflammatory drugs.

With regard to the first point, there are a plethora of studies that suggest that diets high in Mg do protect against stroke, particularly in hypertensive men. On the other hand, a 1993 Austrian study indicated that Mg supplements did not influence serum Mg.

The team also pointed out that the combined study endpoint of any ischemic stroke and carotid revascularization may include different pathophysiological entities, although the majority of the events were due to macrovascular diseases such as coronary disease, cerebrovascular disease, and peripheral vascular disease. They suggested that further studies on larger patient populations need to be done to confirm their findings and to distinguish between the different entities of neurological events.

Despite the limitations of the study, researchers concluded: "Low serum Mg levels (<0.76mmol/L) are a risk factor for neurological events in patients with symptomatic PAD, favouring Mg substitution therapy in those patients with advanced atherosclerosis." They noted, however, that the data on the potential benefits of oral Mg substitution is controversial.