Does a low sodium diet improve asthma control? A randomized controlled trial.
BACKGROUND
Observational studies and initial randomized trials have indicated that a low sodium diet may improve asthma control.


OBJECTIVE
We tested the hypothesis that a low sodium diet would improve asthma control over a 6-week period.


METHODS
Participants with a physician diagnosis of asthma and measurable bronchial reactivity to methacholine entered a randomized double-blind placebo-controlled trial. All adopted a low sodium diet and were randomized to receive either 80 mmol/day of oral sodium supplements (normal sodium intake) or matched placebo (low sodium intake) for 6 weeks. The primary outcome was change in bronchial reactivity to methacholine; secondary outcomes were change in lung function, morning and evening peak expiratory flow, asthma symptoms score, daily bronchodilator use, Juniper Standardized Asthma Quality of Life Questionnaire score, and atopy.


RESULTS
A total of 220 individuals entered the study, of whom 199 completed the protocol. In the low sodium-intake group, mean daily urinary sodium excretion decreased by 20 mmol (SD, 64 mmol) and in the normal-sodium-intake group increased by 28 mmol (SD, 74 mmol). There were no differences between the two groups in the primary or secondary outcome measures; the mean difference in bronchial reactivity between the low- and normal-intake groups was -0.03 doubling doses of methacholine (95% confidence interval, -0.60 to 0.53).


CONCLUSIONS
The use of a low sodium diet as an adjunctive therapy to normal treatment has no additional therapeutic benefit in adults with asthma and bronchial reactivity to methacholine.
Pogson
Zara E K
ZE
Division of Epidemiology and Public Health, University of Nottingham, Clinical Sciences Building, Nottingham City Hospital, Nottingham, NG5 1PB, UK. zara.hoare@nottingham.ac.uk
Antoniak
Marilyn D
MD
Pacey
Sarah J
SJ
Lewis
Sarah A
SA
Britton
John R
JR
Fogarty
Andrew W
AW
D000293:Adolescent; D000328:Adult; D000368:Aged; D001249:Asthma / Q000517:prevention & control*; D001985:Bronchial Provocation Tests; D004039:Diet, Sodium-Restricted; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis