Background: Caffeine has a variety of pharmacological effects. It is chemically related to the drug theophylline which is used to treat asthma. Accordingly, interest has been expressed in its potential role as an asthma treatment. A number of studies have explored the effects of caffeine in asthma, this is the first review to systematically examine and summarise the evidence.
Objectives: Caffeine is a weak bronchodilator and it also reduces respiratory muscle fatigue. It has been suggested that caffeine may reduce asthma symptoms. The objective of this review was to assess the effects of caffeine on lung function and identify whether there is a need to control for caffeine consumption prior to lung function testing.
Search strategy: We searched the Cochrane Airways Group trials register and the reference lists of articles. We also contacted study authors.
Selection criteria: Randomised trials of oral caffeine compared to placebo in adults with asthma.
Data collection and analysis: Trial quality assessment and data extraction were done independently by two reviewers.
Main results: Six trials involving a total of 55 people were included. The studies were all of cross-over design and of high quality. In comparison with placebo, caffeine appears to improve lung function for up to two hours after consumption. Forced expiratory volume in one minute showed a small improvement up to two hours after caffeine use (standardised mean difference -0.73, 95% confidence interval -1.20 to -0.25). Mid-expiratory flow rates also showed a small improvement with caffeine and this was sustained up to four hours. An updated search in June 2001 did not identify any further studies.
Reviewer's conclusions: Caffeine appears to improve airways function modestly in people with asthma for up to four hours. People may need to avoid caffeine for at least four hours prior to lung function testing.