To evaluate putatively beneficial effects of coffee on human health, intervention studies are conducted. To correlate possible short term effects of consumption, the subjects need to run through washout periods prior to the coffee intervention to serve as their own control. The coffee constituents trigonelline and iV-methylpyridinium (NMP) were identified as compounds contributing most to the dissimilarities between the urine of coffee drinkers and non-coffee drinkers. Application of a developed stable isotope dilution assay in a coffee intervention study revealed significantly higher values of trigonelline and NMP (normalized to creatinine) in coffee drinker urine for up to 48 h and 72 h, respectively, when compared to non-coffee drinkers, proposing these two compounds as indicators for coffee consumption. Further investigations demonstrated, that trigonelline and NMP can be detected in human salivary fluid for ～16 h. According to acquired food data, roast coffee appears to be the predominating source for trigonelline and NMP in human diet.
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