The effect of caffeinated coffee on airway response to methacholine and exhaled nitric oxide

SummaryBackgroundThe bronchoprotective effect of caffeine on histamine challenge testing (HCT) has been studied with equivocal results. Current guidelines for bronchoprovocation testing recommend exclusion of caffeine the day of testing. The effects of caffeine on methacholine challenge testing (MCT), now more commonly performed than histamine challenge, are unknown.MethodsSixteen well-controlled asthmatics with a forced expiratory volume in 1 s (FEV1) > 65% predicted and methacholine provocation concentration causing a 20% fall in FEV1 (PC20) ≤ 16 mg/ml participated in a randomized single-blind crossover study. The two treatments included 16 ounces of caffeinated and decaffeinated coffee given on two separate days. The fraction of exhaled nitric oxide (eNO) and FEV1 were measured before and 1 h after each treatment. One hour post treatment blood was drawn for serum caffeine level and the MCT was done.ResultsFourteen subjects completed the study; there were no adverse events. No significant bronchodilation was seen between the mean FEV1 values before and after the caffeinated treatment (3.31 ± 0.75 L and 3.36 ± 0.74 L, respectively). No significant bronchoprotection was seen between the caffeinated and decaffeinated treatment's geometric mean PC20 values (1.35 mg/ml and 1.36 mg/ml, respectively). Mean eNO values before and after caffeinated treatment were not significantly different (31.2 ± 19.6 ppb and 31.5 ± 20.4 ppb).ConclusionThe amount of caffeine in a normal dietary serving of a 16oz cup of coffee is not enough to cause significant bronchoprotection, bronchodilation, or decrease eNO values. Registered at http://clinicaltrials.gov: NCT01057875.