Magnesium is fourth on the list of the most abundant cations in the body (following calcium, sodium, and potassium), and it is second only to potassium as the most abundant intracellular cation. It is an essential cofactor in more than 300 different enzymatic reactions, including carbohydrate utilization, ATP metabolism, muscle contraction, transmembrane ion transport (calcium, sodium, chloride, potassium), and the synthesis of fat, protein, and nucleic acids. Magnesium also appears to play an important role in lung function. In a large study of adults selected randomly from the general population, Britton et al. found that high dietary magnesium intake was independently associated with better lung function and less asthma and wheezing.
The investigators calculated dietary magnesium intake (by food frequency questionnaire) and evaluated lung function and atopy in 2633 volunteers aged 18 to 70 years. Lung function was measured as one-second forced-expiratory volume (FEV1) and by airway reactivity to inhaled methacholine. Atopy was measured as skin-prick response to three environmental allergens. Subjects described their respiratory symptoms and gave social, medical, occupational, and smoking histories.
Mean magnesium intake was 380 mg/day, although intake varied widely and was significantly lower in females than males. Intake also decreased significantly with increasing age. After adjusting for age, sex, height, and the effects of atopy and smoking, the investigators found that a 100 mg/day higher magnesium intake was associated with a significantly higher FEV1 and a reduction in lung hyperreactivity. Magnesium has several antiasthmatic actions: as a calcium antagonist it relaxes airway smooth muscle (in vitro) and dilates bronchioles (in vivo). It also inhibits cholinergic transmission, increases nitric oxide release, and reduces airway inflammation (by stabilizing mast cells and T- lymphocytes). The investigators concluded, “Low magnesium intake may therefore be involved in the etiology of asthma and chronic obstructive airways disease.”
Dietary magnesium is obtained from cereals, nuts, green vegetables, and dairy products. However, according to Britton et al., a substantial amount is lost in cooking or in refining foods. Diets high in refined or processed foods are thus likely to be low in magnesium. Magnesium deficiency is surprisingly common. In one study, hypomagnesemia was found in 65% of an intensive care population and 11% of an outpatient population. Magnesium is used pharmacologically in acute myocardial infarction, angina, cardiac arrhythmias, alcohol withdrawal, and pre-eclampsia. It has been used to treat acute asthma, and now it appears that magnesium may also help prevent asthma.