Magnesium, Sudden Cardiac Death Risk

Bonnie and Steve - In January 2007, we made an impassioned plea for our readers to spread the word about the connection between magnesium and thirty-something's dropping dead from sudden cardiac death (article here). We were rebuked for the strong wording of the piece. Almost four years later, a study in this month's American Heart Journal supports our call to action. While the subject group was a bit older (45-64), this should be a wake up call, especially for those who are very active physically, to supplement with magnesium. Along with vitamin D, magnesium is the most deficient nutrient in Americans. Simply put, for maintaining good magnesium levels, diet is not going to cut it.

American Heart Journal Study Summary
Researchers hypothesized that serum magnesium (Mg) is associated with increased risk of sudden cardiac death (SCD). The Atherosclerosis Risk in Communities Study assessed risk factors and levels of serum Mg in a cohort of 14,232 45- to 64-year-old subjects in 1987–1989. After an average of 12 years of follow-up, we observed 264 cases of SCD.

Individuals in the highest quartile of serum Mg were at significantly lower risk of SCD in all models. This association persisted after adjustment for potential confounding variables, with an almost 40% reduced risk of SCD in quartile 4 versus 1 of serum Mg observed in the fully adjusted model.

The study suggests that low levels of serum Mg may be an important predictor of SCD. Further research into the effectiveness of Mg supplementation for those considered to be at high risk for SCD is warranted.

Details

Sudden cardiac death (SCD) is a major public health problem comprising more than half of all cardiovascular disease (CVD) deaths in the United States.

Magnesium (Mg), a micronutrient and common cation in the human body, is a natural calcium (Ca) antagonist and modulates vasomotor tone, blood pressure, and peripheral blood flow. Although virtually all Mg is stored in cells, low levels of serum Mg are usually predictive of low levels of total body Mg as well. Previous epidemiologic studies have reported that serum and dietary Mg is associated inversely with CVD risk factors such as hypertension, type 2 diabetes mellitus, and the metabolic syndrome, in addition to CHD. Additional evidence from ecologic, clinical, and autopsy studies has shown higher Mg to be potentially protective against SCD; but no prospective studies have reported the association of Mg levels with incidence of SCD in the general population. In addition to its role in the regulation of blood pressure and maintenance of vascular smooth muscle tone, Mg deficiencies are known to cause ventricular arrhythmias, the most common precursors to SCD. Serum Mg levels are modified by intake of dietary Mg, Ca, and potassium (K), in addition to alcohol intake and physical exercise.

The main finding from this analysis was a significantly reduced risk of SCD in the highest quartile compared with the lowest quartile of serum Mg in a prospective cohort with >173,000 person-years of follow-up. This association persisted after adjustment for the major predictors of SCD and potential confounders (or mediators) of the Mg-SCD relationship, including hypertension, diabetes, serum K, heart rate–adjusted QT interval, and use of diuretics. The association was monotonic, with a declining risk of SCD with each quartile of higher serum Mg. This association did not differ by race, sex, prevalent CHD, use of diuretics, serum K level, or heart rate–adjusted QT interval. Despite these strong findings for serum Mg, we observed no association between dietary Mg and risk of SCD. This is not surprising given previous reports from this cohort showing no association of dietary Mg with either incident hypertension or CHD, despite associations of these outcomes with serum Mg.

Individuals who maintained serum Mg levels higher than the median value at 2 visits 3 years apart had the lowest risk of SCD. Nevertheless, a limitation of our study was an inability to assess levels of serum Mg just before an event. It could be that a sudden drop in Mg is important. However, measurement just before SCD is not possible in a prospective study. Serial measurements of serum Mg over many years would improve our ability to understand the impact of short-term transient changes in serum Mg on the risk of SCD.