USUAL DIETARY SALT INTAKE AND ASTHMA IN CHILDREN - A CASE-CONTROL STUDY

Background - A decline in host resistance due to an alteration in diet - primarily of salt - was recently put forward as a possible explanat ion for rising rates of asthma. Methods - A case-control study was cod ucted in participants in a prevalence survey which included 187 childr en with asthma (defined by prior diagnosis and/or a decline in forced expiratory volume in one second (FEV(1)) of greater than or equal to 1 0% after exercise) and 145 age and sex matched controls. Subjects were selected from 989 children aged 5-13 years attending 18 elementary sc hools on the island of Montreal. Usual dietary salt intake was estimat ed from a food frequency questionnaire administered to the mother, and a salt intake score was used to group the children into quartiles fro m I (lowest) to IV (highest salt intake). Bronchial hyperresponsivenes s to methacholine was assessed by Yan's method. Cases and controls wer e combined in one group to examine the relationship of salt intake to bronchial hyperresponsiveness to methacholine. Methacholine responsive ness was expressed as a dose-response slope and ranks of dose-response slopes were used in the analysis. Results - After accounting for impo rtant confounding variables, there was no association between asthma a nd salt intake, while methacholine dose-response slope ranks increased with increasing salt intake and methacholine responsiveness was great er in the highest quartile than in the lowest quartile of salt intake. The median dose-response slopes in % fall in FEV(1) per mu mol methac holine for quartiles I, II, III, and IV were 5.4, 5.9, 7.7, and 8.7. C onclusions - No association was found between asthma or exercise-induc ed bronchospasm and dietary salt intake. Bronchial hyperresponsiveness to methacholine did, however, appear to increase with greater salt in take, but the relevance of this association to asthma is unclear.