Summary: Exercise-induced asthma (EIA), also known as exercise-induced bronchoconstriction (EIB), is a narrowing of the airways with increased airway resistance resulting in decreased pulmonary function post exercise. Sixteen subjects volunteered for this study, eight with clinically diagnosed EIA and 8 without. The study was conducted as a randomized double-blind crossover trial over 5 weeks. The first 2 weeks the subjects were randomly placed on a high salt diet (HSD) or low salt diet (LSD), followed by a one week "wash out" period on their normal diet (NSD), followed by another two weeks on the alternative diet. A 24-hour urine collection was collected at the end of each period. The exercise test protocol was a standard graded protocol of incremental increasing workloads. The test lasted approximately 10mins and consisted of running on a treadmill at 85-90% of age-predicted maximum heart rate. Pulmonary function was tested pre-exercise and at 1, 5, 10 and 15 min post exercise. Findings: Both groups, EIA and control subjects, had similar pre-exercise pulmonary function values. EIA subjects had decreased FVC, FEV1, and PEFR post-exercise on all diets at all post-exercise times. The type of diet was shown to influence the range of decrements in the pulmonary function values. The largest decrements were recorded while on the HSD with the numbers improving slightly on a NSD and a little more on the LSD. Salt loading regardless of the type, either sodium chloride or sodium citrate, worsened symptoms of asthma and increased the use of inhaled steroids. The higher the salt intake, the greater the severity of the asthma. Restricting salt intake did not normalize the symptoms of EIA though. Implications: Asthmatics should carefully monitor their salt intake in order to help control they symptoms and severity of their asthma.
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