Urinary Excretion of Niacin Metabolites in Humans After Coffee Consumption

Scope: Coffee is a major natural source of niacin in the human diet, as it is formed during coffee roasting from the alkaloid trigonelline. The intention of our study was to monitor the urinary excretion of niacin metabolites after coffee consumption under controlled diet. Methods and results: We performed a 4-day human intervention study on the excretion of major niacin metabolites in the urine of volunteers after ingestion of 500 mL regular coffee containing 34.8 mu mol nicotinic acid (NA) and 0.58 mu mol nicotinamide (NAM). In addition to NA and NAM, the metabolites N1-methylnicotinamide (NMNAM), N-1-methyl-2-pyridone-5-carboxamide (2-Py), and nicotinuric acid (NUA) were identified and quantified in the collected urine samples by stable isotope dilution analysis (SIVA) using HPLC-ESI-MS/MS. Rapid urinary excretion was observed for the main metabolites (NA, NAM, NMNAM, and 2-Py), with t(max) values within the first hour after ingestion. NUA appeared in traces even more rapidly. In sum, 972 nmol h(-1) of NA, NAM, NMNAM, and 2-Py were excreted within 12 h after coffee consumption, corresponding to 6% of the ingested NA and NAM. Conclusion: The results indicate regular coffee consumption to be a source of niacin in human diet.