Dietary salt reduction or exclusion for allergic asthma.

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. The most recent search was carried out in February 2004.

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).

MAIN RESULTS

Six RCTs were included in this review. All studies were small size and of short duration. Data from only four studies 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, however the confidence intervals were wide. FEV(1) with low salt compared to normal diet showed a WMD 0.09 L with a 95% confidence interval (95%CI) -0.19 L to 0.38 L, and compared to a high salt diet WMD 0.18 L; 95%CI -0.11 L to 0.48 L. Daily PEFR was also non-significantly higher with low salt diet compared to normal (WMD 19.52 L/min; 95% CI -21.22 to 60.25) and high salt diet (WMD 7.57 L/min; 95% CI -37.52 to 52.67). Reliever bronchodilator with the low salt diet when compared to both the normal and high salt diets showed WMD -0.07 puffs/day; 95%CI -0.94 to 0.81 & WMD -0.65 puffs/day; 95%CI -1.75 to 0.45, respectively.

REVIEWERS' 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. The results of this review do indicate an improvement in pulmonary function with low salt diet, however further large scales trials are required before any firm conclusions can be reach.