Dietary chloride as a possible determinant of the severity of exercise-induced asthma

Dietary sodium chloride (NaCl) has been shown to alter the severity of exer cise-induced asthma, but it is not known if the sodium and chloride ions ha ve independent effects in this regard. The hypothesis tested in the present study was that both a low sodium, low chloride diet and a high sodium. low chloride diet would improve post-exercise pulmonary function in subjects w ith exercise-induced asthma (EIA) compared to a normal NaCl diet (NSD); but that neither of these diets would have an effect on post-exercise pulmonar y function in control (non-EIA) subjects. Eight subjects who suffered from EIA and eight subjects who did not (control) took part in a double-blind cr ossover study. Pre- and post-exercise pulmonary function was assessed after 2 weeks on a NSD, a low NaCl diet (LSD, low sodium, low chloride) or a sod ium bicarbonate diet (NaHCO3 diet, high sodium, low chloride). A 1 week was hout period occurred between diets. Altering dietary sodium or chloride had no effect on pre-exercise (baseline) pulmonary function in either group or on post-exercise pulmonary function in control subjects. However, both the LSD and the NaHCO3 diet lessened the deterioration in post-exercise pulmon ary function in EIA subjects. Comparing results from pre- to postexercise, forced expiratory volume in 1 s (FEV1) at 15 min post-exercise differed sig nificantly (P < 0.05) between diets [mean (SEM) 7 (4)% on the LSD, 14 (4)% on the NaHCO3 diet, and 19 (2)% on the NSD]. Similar patterns were observed for forced vital capacity (FVC), forced expiratory flow rate at 25%-75% FV C and peak expiratory flow rate. The NaHCO3 diet lessened the deterioration of post-exercise pulmonary function, but not to the extent of LSD. These d ata suggest that both sodium and chloride contribute to the worsening of EI A symptoms seen after consuming a normal or high NaCl diet.