Your morning cup o' joe could be more than just a quick pick-me-up. In an article in the Cochrane Database of Systematic Reviews, British scientists reviewed the evidence on asthma and caffeine. They found that caffeine slightly improves airway function in people with asthma. The effect lasts for at least two hours after a moderate amount of caffeine—about the amount in two to three cups of coffee.
It turns out that the caffeine in coffee is a weak bronchodilator—that is, it is modestly effective in opening your airways. Caffeine also may mildly fight fatigue in your breathing muscles.
The improvement is small, however. Scientists still don't know whether it's substantial enough to help you feel noticeably better. But they do know that coffee is no substitute for your asthma medication.
Drinking a lot of coffee has a downside, too. Some people with asthma also have gastroesophageal reflux disease (GERD), and caffeine can make that condition worse.
Even if you don't have GERD, excessive caffeine may cause anxiety, trouble sleeping, upset stomach, shakiness, and rapid heartbeat. Limit yourself to no more than two to three cups of coffee per day.