A study called "The effect of caffeine in people with asthma" examined the theoretical bronchodilator effect of caffeine on subjects suffering from a mild or moderate form of asthma.
There have been seven studies, with a total of 75 people, and have foreseen the use of the spirometry technique.
Six studies involving 55 subjects show that, compared to placebo, moderate caffeine dosages (5mg / kg body weight) also seem to improve lung function up to two hours after consumption.
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The parameter of "Forced Expiratory Volume in the first second" (FEV1) showed an improvement (albeit modest, 5% FEV1) that persevered up to two hours after ingestion of caffeine.
On the other hand, in two other studies, following the intake of caffeine, the average differences in FEV1 were 12-18%. There was also a small improvement in the "Mid-Expiratory Flow", which was maintained for around four hours.
A final study, on the other hand, involved 20 subjects and examined the effect of normal and decaffeinated coffee on nitric oxide (NO) levels. Nitric oxide is a chemical mediator (produced by the enzyme nitric oxide synthase starting from the amino acid arginine) which, among the various functions, "potentially" also plays the role of bronchial dilator.
There was no significant effect.
Ultimately, in asthmatic subjects, caffeine seems to slightly favor the function of the airways for a maximum of four hours. This means that, in the assessment exams, people should avoid using foods or drinks containing caffeine, as this could cause an error in the interpretation of the spirometric parameters.
On the other hand, drinking coffee containing caffeine before estimating nitric oxide concentrations does not seem to influence the results of the test in any way, even if to confirm this result it is necessary to carry out further investigations of an experimental nature.