Burney 1989.

Methods	Randomised placebo‐controlled cross‐over study. .
Participants	36 participants (14 men, 22 women) with moderately severe asthma were included in the study. Age range 18 to 53 years. 9 current smokers, 10 ex‐smokers and 17 never smoked. 35 subjects on inhaled bronchodilators and 12 using inhaled steroids.
Interventions	After one week run‐in, subjects were put on a low sodium diet and asked to take either slow sodium tablets (80 mmol/day) or placebo. After a 2‐week period the subjects were crossed over (no wash‐out period). Study measurements were performed after the run‐in period, 2 weeks after first intervention and 2 weeks after the secondary intervention. Exclusion criteria: none stated in the paper.
Outcomes	FEV1, FVC, PD20, PD10, skin prick tests and blood pressure.
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	No information given in paper.
Allocation concealment (selection bias)	Unclear risk	Described as randomised; no other information available.
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Described as blinded; no other information available.
Incomplete outcome data (attrition bias) All outcomes	High risk	5 subjects were excluded but not included in the analysis.
Selective reporting (reporting bias)	Unclear risk	Not clear from the information presented.
Other bias	Unclear risk	The significant results are only present in men and has no calculation of power described. There was no wash‐out period.