Large epidemiological studies suggest a relationship between magnesium and blood pressure. However, the fact that foods high in magnesium (see Sources) are frequently high in potassium and dietary fiber has made it difficult to evaluate independent effects of magnesium on abnormally high blood pressure (‘hypertension’).
A prospective cohort study of more than 30,000 male health professionals found an association between lower dietary fiber, potassium, and magnesium intakes, and a higher risk of developing hypertension over a four-year period (6). In a similar study of more than 40,000 female registered nurses, higher dietary fiber and dietary magnesium intakes were each associated with lower systolic and diastolic blood pressures in those who did not develop hypertension over the four-year study period, but neither dietary fiber nor magnesium was related to the risk of developing hypertension (7).
The Atherosclerosis Risk in Communities (ARIC) study examined dietary magnesium intake, magnesium blood levels, and risk of developing hypertension in 7,731 men and women over a six-year period (8). The risk of developing hypertension in both men and women decreased as blood serum magnesium levels increased, but the trend was only statistically significant in women.
Although the investigators found no association between dietary magnesium and the incidence of hypertension, they suggested that low blood magnesium levels may play a modest role in the development of hypertension.
Cardiovascular disease
A number of studies have found decreased mortality from cardiovascular diseases in populations who routinely consume ‘hard’ (‘alkaline’) water, generally high in magnesium, calcium and fluoride; this makes the heart-protective effects of hard water difficult to attribute to magnesium alone (9).
One large prospective study with almost 14,000 men and women found a significant trend for increasing blood serum magnesium levels to be associated with decreased risk of coronary heart disease in women but not in men (10). However, the risk of coronary heart disease in the group with the lowest intake of dietary magnesium intake was not significantly higher than the risk in men or women with the highest intake.
Additionally, a large prospective study in over 35,000 women reported that dietary magnesium, assessed by food frequency questionnaire, was not associated with risk for various cardiovascular diseases (e.g. stroke, myocardial infarction, and coronary heart disease) (11).
Presently, the relationship between dietary magnesium intake and the risk of cardiovascular disease remains unclear.