Summary of findings 1. Summary of findings: β‐carotene compared with placebo for chronic pulmonary infection in cystic fibrosis.

β‐carotene compared with placebo for chronic pulmonary infection in cystic fibrosis
Patient or population: children and adults with cystic fibrosis Settings: outpatients Intervention: oral β‐carotene supplementation Comparison: placebo
Outcomes	Illustrative comparative risks* (95% CI)		Relative effect (95% CI)	No of participants (trials)	Quality of the evidence (GRADE)	Comments
	Assumed risk	Corresponding risk
	Placebo	β‐carotene
Pulmonary exacerbations Days of antibiotic use Follow‐up: 3 months	The mean number of days of antibiotics was 18.5 days in the control group.	The mean number of days of antibiotics in the intervention group was 8 days lower (18.8 days lower to 2.78 days higher).	MD ‐8.00 (‐18.78 to 2.78)	24 (1)	⊕⊕⊝⊝ lowa,b	The authors of this paper defined pulmonary exacerbations by the number of days of antibiotics. Pulmonary exacerbations were less frequent in the intervention group but this was not statistically significant (P = 0.15).
Respiratory function absolute FEV1 % predicted Follow‐up: 3 months	The mean FEV1 % predicted was 80.9% in the control group.	The mean FEV1 % predicted in the intervention group was 10.9% lower (32.2% lower to 10.4% higher).	MD ‐10.90 (‐32.23 to 10.43)	24 (1)	⊕⊕⊝⊝ lowa,b	The results favour the placebo for effect on FEV1 but this was not significant (P = 0.32).
Adverse events Follow‐up: 6 months	See comments.			24 (1)	⊕⊕⊝⊝ lowa,b	There were no adverse events reported during the trial. Some participants reported better tanning after exposure to sunlight. No further data were provided for adverse events.
Need for antibiotics see pulmonary exacerbations	See comments.					This outcome was reported by the authors as their definition of pulmonary exacerbations. The number of days of antibiotics was less in the β‐carotene group but not significantly so (P = 0.15).
QoL	This outcome was not measured.
Sputum microbiology	This outcome was not measured.
Inflammatory markers	This outcome was not measured.
*The basis for the assumed risk (e.g. the median control group risk across trials) is provided in footnotes. The corresponding risk (and its 95% CI) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; FEV1: forced expiratory volume in 1 second; MD: mean difference; QoL: quality of life.
GRADE Working Group grades of evidence High quality: further research is very unlikely to change our confidence in the estimate of effect. Moderate quality: further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. Low quality: further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. Very low quality: we are very uncertain about the estimate.

^a Downgraded once due to risk of bias within the included trial, particularly from uncertainty of randomisation method and allocation concealment.
^b Downgraded once due to imprecision. The trial had a small number of participants which is well below the optimal information size and low event rates.