Dietary salt reduction or exclusion for allergic asthma

Abstract

Background: There is a wide geographical variation in asthma prevalence and one explanation may be in dietary salt consumption.

Objectives: To assess the effect of dietary sodium reduction in patients with asthma.

Search strategy: A search was conducted using the Cochrane Airways Group asthma register. Bibliographies of included randomised controlled trials (RCTs) were searched for additional studies. Authors of identified RCTs were contacted for other studies.

Selection criteria: All studies were to be RCTs that involved dietary salt reduction or increased salt intake in patients with asthma. Studies of other allergic conditions such as hay fever, allergic rhinitis and eczema were considered patients with asthma were separately identified.

Data collection and analysis: Study quality was assessed and data extracted by two reviewers. All data analysis was conducted using the Cochrane Collaboration software (RevMan 4.1.1).

Main results: Fifty-six abstracts were identified and 15 studies were reviewed in full text. Five fulfilled the inclusion criteria. Nine were excluded. One was published in duplicate. Complete agreement was reached between the reviewers on inclusion or exclusion of all studies. All studies were small and of short duration. Data from only three could be pooled. Low sodium diet was associated with a significantly lower urine sodium excretion than normal or high salt diets. There were no significant differences in any asthma outcome between low salt and normal or high salt diets, but FEV1 was slightly higher with low salt compared to normal, WMD 0.09 L (95% confidence interval (CI) -0.26, 0.44 L, n=88), as was daily PEFR, WMD 11 l/min (95% CI -81, 103 l/min, n=78). With low compared to high salt, FEV1 was slightly higher WMD 0.22 L (95% CI -0.14, 0.59 L, n=88), as was daily PEFR, WMD 14 l/min (95% CI -41, 68 l/min, n=78). Bronchodilator use was slightly lower, WMD 0.7 puffs/day (95% CI -1.8, 0.5 puffs/day, n=62).

Reviewer's conclusions: Based on currently available evidence it is not possible to conclude whether dietary salt reduction has any place in the treatment or management of asthma.