In contrast to the results of small clinical trials, asthma patients who follow a low-sodium diet as an adjunct to normal treatment do not have any related improvement in their symptoms, according to a new report published in the July 15 issue of the American Journal of Respiratory and Critical Care Medicine.

Zara E.K. Pogson, of the University of Nottingham in Nottingham, U.K., and colleagues conducted a study of 199 asthma patients who began a low-sodium diet and were randomized to either 80 mmol/day of oral sodium supplements (representing normal sodium intake), or placebo for six weeks.

The outcomes included bronchial reactivity to methacholine, change in lung function, morning and evening peak expiratory flow, asthma symptoms score and daily bronchodilator use. The investigators found that results were similar for both groups.

"Our pragmatic randomized controlled trial of the role of a low-sodium diet on asthma control did not show any evidence of a therapeutic benefit, despite a differential in 24-hour urinary excretion of 50 mmol between the intervention and control group at the end of the intervention in those who completed the study," the authors write. "We cannot exclude the possibility that a low-sodium diet may improve asthma control in those who either consume higher baseline levels of dietary sodium or can achieve a greater decrease in dietary sodium intake than we observed."

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