title: Urinary caffeine after coffee consumption and heat dehydration.
abstract: This study evaluated the effect of heat-induced dehydration on urinary caffeine excretion after the consumption of a strong coffee solution. Following ingestion of coffee (caffeine 4.9+/-0.1 [SE] mg/kg, 3-4 cups), ten healthy males were intermittently exposed to heat in a sauna until they had lost 2.9 % of lean mass. On a separate occasion, they consumed the same amount of coffee but remained quiet and euhydrated (control). Urine flow was reduced 7-fold in dehydration. At these low excretion rates (< 30 ml/h), caffeine concentration was negatively correlated with flow. Peak urinary caffeine (Cmax) was 7.6 +/- 0.4 (SE) microg/ml in dehydration and 7.1 +/- 0.2 microg/ml in the control (p > 0.05). Compared with the control, dehydration delayed Cmax by 1 hour, maintained higher saliva caffeine concentration (6.1 vs 5.2 microg/ml, p < 0.05) and a lower saliva paraxanthine/caffeine ratio (p < 0.001). The 24h-recovery of caffeine in urine was reduced (1.2 vs 2.8% of dose, p < 0.001), however at least 2.6% of dose were lost in sweat. These results suggest that the rise in circulating caffeine due to delayed metabolic clearance was partly opposed by a sizeable elimination in sweat. Therefore, heat dehydration did not lead to higher concentration of caffeine in urine after coffee ingestion.
authors.affiliation: Nestlé Research Centre, Nestec Ltd, Lausanne, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Chambaz
authors.forename: I
authors.initials: I
authors.lastname: Meirim
authors.forename: J
authors.initials: J
authors.lastname: Décombaz
mesh_terms: D000328:Adult; D002110:Caffeine / Q000008:administration & dosage / Q000378:metabolism / Q000652:urine*; D016022:Case-Control Studies; D002851:Chromatography, High Pressure Liquid; D003069:Coffee; D003681:Dehydration / Q000503:physiopathology*; D006358:Hot Temperature; D006801:Humans; D008297:Male; D012463:Saliva / Q000737:chemistry; D018709:Statistics, Nonparametric; D029002:Steam Bath; D013542:Sweat / Q000737:chemistry
chemical_list: D003069:Coffee; D002110:Caffeine