Urinary caffeine and caffeine metabolites and lung function in a nationwide study of U.S. adults

Abstract

<b>Background:</b> Coffee contains caffeine and xanthines with similar properties to theophylline, a mild bronchodilator that was used for asthma treatment. Whether caffeine or caffeine metabolites lead to improvements in lung function is largely unknown. <b>Objective:</b> To examine urinary levels of caffeine and caffeine metabolites, asthma, and lung function in adults. <b>Methods:</b> Cross-sectional study of 2,832 adults aged 18-80 years in the US National Health&nbsp;and Nutrition Examination Survey (NHANES). Multivariable logistic or linear regression&nbsp;was used to examine the relation between urinary caffeine and three major caffeine metabolites (paraxanthine, theobromine, and theophylline) and asthma or lung function measures. <b>Results:</b> Urinary paraxanthine levels in the fourth quartile (Q4) were significantly associated with 53% lower odds of asthma (95% CI= 0.23 to 0.98). Among adults without asthma, each increment in the interquartile range (IQR) of paraxanthine were associated with 0.69% and 1.06% increment in percent predicted (%pred) FEV1 and FVC, while each increment in the IQR of theophylline was associated with 0.94% increment in %pred FVC. Among adults with asthma, each increment in the IQR of urinary of caffeine, paraxanthine, or theophylline were associated with 2.32% to 3.17% decreased %pred FEV1/FVC. <b>Conclusions:</b> Among adults in NHANES, a high urinary paraxanthine was associated with lower odds of asthma, and higher urinary levels of paraxanthine or theophylline were associated with increased FEV1 and FVC in adults without asthma. On the other hand, higher urinary levels of caffeine, paraxanthine, or theophylline were associated with decreased FEV1/FVC in adults with asthma.