Investigation of the effect of short-term change in dietary magnesium intake in asthma.

Epidemiological evidence suggests that a low dietary intake of magnesium is associated with impaired lung function, bronchial hyperreactivity and wheezing. This study was designed to investigate whether short-term alterations of dietary magnesium intake have an effect on the clinical control of asthma. In a randomized, double-blind, placebo-controlled, cross-over study, 17 asthmatic subjects adhered to a low magnesium diet for two periods of 3 weeks, preceded and separated by a 1 week run-in/wash-out, in which they took either placebo or magnesium (400 mg x day(-1)) tablet supplementation. Forced expiratory volume in one second (FEV1) and the provocative dose of methacholine required to cause a 20% fall in FEV1 from baseline (PD20,FEV1) were measured at the beginning and end of each treatment period, and variation in peak expiratory flow (PEF) rate, bronchodilator use and symptom scores recorded throughout. Asthma symptom scores were significantly lower during the magnesium treatment period, the median (95% confidence interval) difference from placebo being 3.8 (0.5-7.0) symptom points per 7 days (p=0.02). However, there was no significant improvement in FEV1, PD20,FEV1, log amplitude percentage mean PEF variation or bronchodilator use during magnesium supplementation. A high magnesium intake was associated with improvement in symptom scores, though not in objective measures of airflow or airway reactivity, in these stable asthmatic subjects.