Caffeine is a naturally occurring compound. The German analytical chemist Friedrich Ferdinand Runge (1795–1867) discovered caffeine in 1819, apparently at the urging of Gœthe, who had encouraged Runge to study and analyze coffee.
We now know that caffeine is naturally present in foods such as coffee beans, tea leaves, cacao beans (used to make chocolate), kola nuts, guarana, and maté. Caffeine is also frequently added to beverage products, such as carbonated soft drinks and drinks marketed as energy drinks. It is also available in pill form, either alone (NoDoz, Vivarin), or as an additive, to aspirin for example, as in Anacin and Excedrin.
Research studies of the effect of caffeine in humans confirm that caffeine is a bronchodilator. It improves pulmonary function, and although it is a weak bronchodilator, it clearly has beneficial effects on direct measurements of lung function, such as the vital capacity, the FEV1, and expiratory flows.
Studies of the human metabolism of caffeine reveal that ingested caffeine is metabolized by the body and transformed into three separate compounds. Caffeine metabolites are paraxanthine, theobromine, and theophylline. Theophylline is a well-known bronchodilator, used in pill form for decades in the treatment of several lung ailments, including asthma, chronic obstructive bronchitis, and emphysema. The effects of orally administered caffeine are maximal at about 2 hours after ingestion and wear off after approximately 6 hours.
Incidentally, if you are undergoing pulmonary function testing as part of an evaluation of possible asthma, you should avoid caffeine for at least 4 hours prior to lung testing. So, to get back to the question about caffeine being good for people with asthma—if you enjoy caffeinated beverages, know that the caffeine they contain will, if taken in high enough doses, provide bronchodi-latation and possibly modestly improve your lung function. Sounds good to me!