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

Abstract

Objective

Coffee intake has been inversely associated with asthma in adults. We examined the relation between urinary levels of caffeine or caffeine metabolites and asthma, lung function, and fractional exhaled nitric oxide (FeNO) in adults.

Methods

Cross-sectional study of 2,832 adults aged 18-79 years in the US National Health and Nutrition Examination Survey (NHANES). Multivariable logistic or linear regression was used for the analysis of urinary levels of caffeine or each of its three major metabolites (paraxanthine, theobromine, and theophylline) and current asthma, lung function, and FeNO.

Results

Subjects with urinary paraxanthine levels in the fourth quartile (Q4) had 53% lower odds of current asthma than those whose urinary paraxanthine levels were in the first quartile (Q1; 95% confidence = 0.22 to 1.00). Among never and former smokers, subjects with urinary theophylline levels above Q1 had 49% lower odds of current asthma than those whose urinary theophylline level was in Q1 (95% CI = 0.31 to 0.85). Among subjects without current asthma, each log₁₀-unit increment in paraxanthine level was associated with a 0.83% increment in percent predicted (%pred) FEV₁ and a 1.27% increment in %pred FVC, while each log₁₀-unit in theophylline was associated with a 1.24% increment in %pred FVC. Neither urinary caffeine nor any urinary caffeine metabolite was associated with bronchodilator response or FeNO.

Conclusions

Our findings suggest that two caffeine metabolites (theophylline and paraxanthine) may contribute to the previously reported inverse association between coffee intake and asthma in adults.

Declaration of interest

Dr. Celedón has received inhaled steroids from Merck in order to provide medications free of cost to participants in an NIH-funded study, unrelated to the current work. The other authors report no conflicts of interest.

Additional information

Funding

Dr. Celedón’s contribution was supported by grants HL117191, HL152475, and MD011764 from the U.S. National Institutes of Health. Dr. Han’s contribution was supported by grant MD011764. Dr. Forno’s contribution was supported by HL 149693.