Caffeine is found in coffee, tea, cola drinks and cocoa. Caffeine is a drug that is very similar to theophylline. Theophylline is a bronchodilator drug that is taken to open up the airways in the lungs and therefore relieve the symptoms of asthma, such as wheezing, coughing and breathlessness. Scientists are interested in finding out whether caffeine has the same effect on the lungs as theophylline.
There are two major reasons why it is important to know if caffeine is a bronchodilator. The first is because it may be beneficial for asthmatics to take caffeine in order to relieve the symptoms of asthma. The second is because consuming caffeine may affect the results of important tests that determine how bad someone's asthma is.
If caffeine acts as a bronchodilator and widens the airways, then a patient who has consumed caffeine before taking the test would show a better result in a lung function test than they would have if they had not consumed any caffeine. The potential problem with this is that if the test results are better than expected doctors may prescribe a lower dose or a weaker drug than is really necessary, which can lead to problems with asthma management.
This review carefully examines all the available high-quality clinical trials on caffeine in asthma. This review was conducted to discover if people should avoid consuming caffeine before taking lung function tests.
This review found that even small amounts of caffeine can improve lung function for up to four hours. Therefore caffeine can affect the result of a lung function test (e.g. spirometry) and so caffeine should be avoided before taking a lung function test if possible, and previous caffeine consumption should be recorded.
It is not known if taking caffeine leads to improvements in symptoms. It may be that in order to improve the symptoms of asthma, caffeine is needed in such large amounts that the drug's adverse effects would become a problem, so more research is needed.
Another clinical trial looked at the effect of caffeine on exhaled nitric oxide levels and found that there is no significant effect, so it appears unlikely that patients would need to avoid caffeine before taking this type of test. However, this is the result of just a single study so more research is needed to clarify this.