Epidemiological and experimental studies have suggested that dietary
salt may play a role in airway responsiveness. We have previously shown that a
low salt diet improves and a high
salt diet exacerbates post-exercise pulmonary function in individuals with
exercise-induced asthma. The aim of this study was to determine the influence of both elevated and restricted
salt diets on pulmonary function during exercise in individuals with
exercise-induced asthma. Nine men and six women participated in this double-blind, crossover study. The participants entered the study on their normal
salt diet and were placed on either a low or high
salt diet for 2 weeks. Each diet was randomized, with a 1 week washout period between diets before crossing over to the alternative diet for 2 weeks. The participants underwent treadmill testing at 85% of their age-predicted heart rate on the normal
salt diet and at the end of each treatment period. Pulmonary function was assessed during exercise by arterial saturation (ear oximetry) and indirect calorimetry. Twenty-four hour urine collections confirmed compliance with the diets. Arterial saturation was reduced on the high and improved on the
low salt diet at higher exercise intensities. Tidal volume and frequency selection during exercise varied with the diets, with a higher tidal volume and lower frequency on the high
salt diet, but a lower tidal volume and higher frequency on the
low salt diet. This suggested greater airway resistance during the high
salt diet. In conclusion, the
low salt diet improved and the high
salt diet exacerbated pulmonary function during exercise in individuals with
exercise-induced asthma. The mechanism of action remains unclear.