Urinary biomarkers for assessing dietary exposure to caffeine.

The feasibility of using metabolites specific to caffeine as urinary biomarkers to be employed in the estimation of dietary caffeine intake is reported. The influence of inter-individual differences in the metabolism of caffeine and the effect of volunteer phenotype on the interpretation of potential biomarkers has been investigated using urinary caffeine metabolite data. This method of phenotype determination accurately reflected the rate constant for the cytochrome P4501A2 (CYP1A2)-catalysed 3-demethylation of caffeine in vivo. Three studies with up to 20 human volunteers demonstrated that a 24-h urine collection after a caffeine dose allows quantification of the metabolites excreted; that the ratios of selected metabolites used to classify the volunteers into fast, intermediate or slow caffeine metabolizers by CYP1A2 phenotype gave a similar result (2:7:3, slow:intermediate:fast) to that found in the general population (1:7:2); and that three metabolites, 1,7-dimethylxanthine, 1,7-dimethyluric acid and 1-methylxanthine, could be studied further as potential biomarkers for caffeine dietary intake.