Asthma is a chronic lung disease that inflames and narrows the airways. Asthma causes recurring periods of wheezing, chest tightness, shortness of breath, and coughing.1
Impact of coffee and caffeine on asthma
Caffeine is known to be a weak bronchodilator, meaning that it dilates, or widens the bronchioles and bronchus slightly, therefore easing the symptoms of asthma mildly. Caffeine also reduces respiratory muscle fatigue, reducing muscle load on the inspiratory muscles, which will slightly ease the effects of asthma. As well as these benefits of caffeine, it is chemically similar to theophylline (also known as 1,3-dimethylxanthine), which is a drug used in asthma treatment; usually the preventative inhaler.
One trial of 20 people studied the effects of drinking caffeine on exhaled nitric oxide levels.2 Nitric oxide is produced throughout the body, including the lungs, to fight inflammation and relax constricted muscles. High levels of nitric oxide in the exhaled breath can mean that the airways are inflamed; a sign of asthma.3 The trial showed no difference between the participants who drank caffeinated coffee, and those who had a decaffeinated placebo.
However, 7 randomized trials involving a total of 75 adults with mild to moderate asthma were carried out, in which one group of patients were given oral caffeine, and the other group were given a placebo, or decaffeinated coffee. 6 of the 7 trials involved 55 people and showed that, in comparison with the placebo, caffeine (even at a low dose of less than 5mg/kg body weight) appeared to improve lung function for up to 4 hours after consumption.
The conclusion of these tests was that although caffeine does not appear to have an effect on nitric oxide levels (although more testing may be needed as the sample size was small), caffeine does appear to improve lung function for up to 4 hours in people with asthma. As a result, people with asthma may need to avoid consuming caffeine for at least 4 hours before a lung function or asthma test, as the caffeine may cause misinterpretation or incorrect results.4