Table 3.

Multivariable analysis of urinary caffeine or caffeine metabolites and lung function measures by asthma diagnosis.

	All participants (n = 2,430)	Without current asthma (n = 2,241)	With current asthma (n = 189)
Lung function measures		β (95% confidence interval), P-value
Caffeine
% predicted FEV₁	0.06 (−0.83, 0.96), 0.89	0.22 (−0.58, 1.02), 0.58	−0.55 (−4.19, 3.09), 0.76
% predicted FVC	0.59 (−0.24, 1.41), 0.16	0.61 (−0.23, 1.45), 0.15	0.84 (−2.08, 3.75), 0.56
% predicted FEV₁/FVC	−0.54 (−1.29, 0.21), 0.15	−0.39 (−1.08, 0.31), 0.26	−1.52 (−3.38, 0.34), 0.11
Paraxanthine
% predicted FEV₁	0.52 (−0.20, 1.43), 0.13	0.83 (0.02, 1.65), 0.04	−1.08 (−5.56, 3.40), 0.63
% predicted FVC	1.21 (0.41, 2.02), <0.01	1.27 (0.40, 2.13), <0.01	0.81 (−2.75, 4.38), 0.65
% predicted FEV₁/FVC	−0.58 (−1.32, 0.16), 0.12	−0.41 (−1.10, 0.28), 0.24	−1.98 (−4.37, 0.42), 0.10
Theobromine
% predicted FEV₁	0.04 (−1.09, 1.17), 0.94	0.11 (−1.16, 1.38), 0.86	−1.33 (−7.16, 4.50), 0.65
% predicted FVC	0.35 (−0.62 , 1.32), 0.47	0.26 (−0.90, 1.42), 0.65	1.04 (−3.06, 5.14), 0.61
% predicted FEV₁/FVC	−0.32 (−1.01, 0.37), 0.35	−0.16 (−0.75, 0.43), 0.58	−2.50 (−5.78, 0.78), 0.13
Theophylline
% predicted FEV₁	0.46 (−0.50, 1.43), 0.34	0.70 (−0.20, 1.61), 0.12	−0.30 (−4.06, 3.46), 0.87
% predicted FVC	1.24 (0.31, 2.18), 0.01	1.24 (0.27, 2.21), 0.01	2.20 (−0.68, 5.10), 0.13
% predicted FEV₁/FVC	−0.77 (−1.64, 0.10), 0.08	−0.53 (−1.37, 0.31), 0.21	−2.40 (−4.48, −0.33), 0.02

Urinary levels of caffeine or its metabolites were first divided by the urinary creatinine level and then log10-transformed.

All models adjusted for annual household income, body mass index, serum cotinine, pack-years of cigarette smoking, use of oral or inhaled steroids in the past 2 days, time of the day when the samples were collected, and (in all participants) asthma diagnosis.