MINNEAPOLIS, MINNESOTA. Sudden cardiac death (SCD) accounts for over half of all deaths from cardiovascular disease in the United States. As the name implies, SCD happens without warning and mostly occurs among people without known cardiovascular disease. However, hypertension, diabetes, obesity, and a family history of myocardial infarction (heart attack) are known to increase the risk of SCD. Now a group of researchers from four American and one Japanese university reports that a high serum magnesium level substantially reduces the risk of SCD.

Their study involved 7,887 women and 6,345 men between the ages of 45 and 64 years when enrolled in the study during the period 1987 � 1989. The baseline examination included a measurement of serum magnesium level (normal range of 1.3 � 2.1 mEq/L or 0.7 � 1.05 mmol/L). During a 12-year follow-up period (173,000 person-years), 264 cases (0.15%/year) of SCD were observed. Among participants with serum magnesium level at 1.5 mEq/L or less (lowest quartile) the incidence was 2.41 events/1000 person-years, while among those with a serum level at 1.75 mEq/L or higher (highest quartile) the incidence was 0.98/1000 person-years. In other words, the incidence of SCD was 55% lower among participants in the highest quartile of serum magnesium level. The risk reduction dropped to 38% after adjusting for numerous variables that could possibly affect the correlation (cholesterol level, QT interval, serum potassium level, physical activity, smoking status, alcohol intake, education level, age, diabetes, hypertension and use of diuretics).

The researchers make several other interesting observations:

• There was no correlation between dietary magnesium intake as measured by a food frequency questionnaire and SCD.

• A higher magnesium levels was associated with a 5% increase in LDL cholesterol, a 3% increase in HDL cholesterol, and an 18% drop in triglycerides.

• A lower magnesium level was associated with smoking, high systolic blood pressure, hypertension, diabetes, lower education level, and being female or African-American.

• Using non-potassium-sparing diuretics for hypertension increases the risk of SCD.

• Diuretics, while being useful in reducing blood pressure, also lead to excessive magnesium loss through urinary excretion.

The researchers conclude that if the association between low serum magnesium levels and risk of SCD is confirmed in other studies, then clinical trials evaluating the impact of magnesium supplementation on SCD should be considered.

Peacock, JM, et al. Serum magnesium and risk of sudden cardiac death in the Atherosclerosis Risk in Communities (ARIC) Study. American Heart Journal, Vol. 160, No. 3, September 2010, pp. 464-70