Salt and asthma
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Asthma
There is evidence that bronchial reactivity in people with asthma is linked with salt intake. A recent review of epidemiological and intervention studies demonstrated that reducing salt intake may help to reduce the severity of an asthma attack and other breathing problems (1). In particular, a randomised double-blind cross-over study found that adopting a low-salt diet for two weeks reduced asthmatics airway hyper-responsiveness (severity of an asthma attack) in men (2) and another randomised double-blind cross-over study of modest salt restrictions for five weeks in men found that this was associated with improved lung function, reduced asthmatic symptoms and medication use and less severe asthmatic attacks (3). The review further reported that an increased dietary intake of sodium may increase the severity of the disease in those people with asthma.
Other epidemiological evidence suggests that the severity of asthma may relate to salt intake in different countries (4) and a more recent study illustrates the mechanism whereby a higher salt intake exacerbates asthma (5).
It seems therefore that, while salt is not a direct cause of asthma, a high salt intake can act as a major aggravating factor.
References
(1) Mickleborough, T.D., & Fogarty, A. (2006). Dietary sodium intake and asthma: an epidemiological and clinical review, International Journal of Clinical Practice, 60, 12, 1616-1624.
(2) Burney P.G., Neild, J.E., Twort C.H. et al, Effect of changing dietary sodium on the airway response to histamine, Thorax, 1989, 44: 36-41.
(3) Carey O J, Locke C, Cookson J B. Effect of alterations of dietary sodium on the severity of asthma in men. Thorax. 1993;48:714-8.
(4) Burney P. A diet rich in sodium may potentiate asthma. Epidemiologic evidence for a new hypothesis. Chest. 1987;91:143S-148S.
(5) Mickleborough T D, Lindley M R, Ray S. Dietary salt, airway inflammation, and diffusion capacity in exercise-induced asthma. Med Sci Sports Exerc . 2005;37:904-14.