Dietary salt intake as a potential modifier of airway responsiveness in bronchial asthma

While pharmacologic treatment of chronic asthma is usually highly effective, medications often have significant side-effects or exhibit tachyphylaxis. Alternative and/or complementary treatments that reduce dependence on pharmacologic medications are of interest in reducing the severity of asthma. This review analyzes the literature that has evaluated dietary salt intake as a potential modifier of the severity of asthma and airway responsiveness. High dietary intakes of salt, greater than 9 g/d, are common in Western civilizations, as is asthma. The question is whether reducing dietary salt intake potentially would improve pulmonary function and airway responsiveness in individuals with asthma. This review details the existing studies in this regard and includes the studies that have evaluated dietary salt on the severity of exercise-induced asthma (exercise-induced bronchoconstriction [E1B]). From a critical analysis of the existing literature, the data that support a role for dietary salt reduction for reducing severity of asthma and airway responsiveness in individuals with asthma is considered encouraging but not clinically convincing. The existing studies have suffered from a variety of experimental and population limitations. In contrast, the data from studies that have altered dietary salt and evaluated severity of EIB in nonatopic individuals is much more convincing. In each study so far, lowering dietary salt has reduced the severity of EIB to subclinical levels. Correspondingly, the supplementing of diets to higher than normal salt intake increased EIB significantly. This review concludes that the data are sufficient to warrant a clinical trial that is properly controlled and randomized to further investigate the influence of dietary salt intake on pulmonary function, airway responsiveness, symptoms, quality of life, and medication requirements in asthma and EIB.