Sodium intake and exercise-induced asthma.

TIMOTHY D. MICKLEBOROUGH, LOREN CORDAIN, ROBERT W. GOTSHALL, and ALAN TUCKER. A Low Sodium Diet Improves Indices Of Pulmonary Function In Exercise-Induced Asthma. JEPonline, 3(2):46-54, 2000. The purpose of this study was to determine if manipulation of dietary sodium could influence the severity of exercise-induced asthma (EIA). Fifteen clinicallydiagnosed EIA subjects participated in a double-blind, crossover trial. Subjects entered the study on a normal salt diet (NSD), and then were placed either on a low salt diet (LSD) or high salt diet (HSD) for two weeks. Each diet was randomized with a 1-wk washout between diets before crossing over to the alternative diet. Subjects performed a treadmill test to 90% of age-predicted maximum heart rate, and this exercise intensity was sustained for 5 min. Preand post-exercise pulmonary function tests were performed following each treatment period. 24-hr urinary sodium excretions were different (p<0.05) for all three diet periods (NSD=3630 mg/day, LSD=958 mg/day, HSD=8133 mg/day). Contrasting preto post-exercise changes in pulmonary function measurements, all forced expiratory volumes and flows improved on the LSD; FVC (+0.95 L), FEV1 (+0.4 L) and FEF25-75% (+0.83 L/s). The HSD induced reductions in FVC (-0.22 L), FEV1 (-0.37 L) and FEF25-75% (-0.55 L/s). In conclusion, a HSD caused an increase in severity of EIA, whereas a LSD represents a potential beneficial therapy for EIA subjects.