Lelo A, Miners J O, Robson R, Birkett D J
Clin Pharmacol Ther. 1986 Jan;39(1):54-9. doi: 10.1038/clpt.1986.10.
The caffeine content of all tea or coffee beverages consumed by 17 healthy adults over 24 hours was measured. Plasma caffeine, theophylline, theobromine, and paraxanthine concentrations were determined over the same 24 hours. The average caffeine content per drink was 60.4 +/- 21.8 mg for instant coffee (14-fold range), 80.1 +/- 19.2 mg for brewed coffee (2.8-fold range), and 28.8 +/- 13.7 mg for tea (5.5-fold range). The number of drinks of coffee and tea consumed was a poor index of actual caffeine intake (r2 = 0.42). Caffeine intake correlated poorly with the 24-hour average caffeine concentration (r2 = 0.41), but there was a very good correlation between a single plasma caffeine concentration measured at 5 PM and the 24-hour average concentration (r2 = 0.94). The same was true for paraxanthine (r2 = 0.86). Paraxanthine accounted for 67.3% of the total dimethylxanthines in plasma, while theobromine and theophylline accounted for 24.4% and 8.3%, respectively. Mean caffeine clearance was 1.2 +/- 0.3 ml/min/kg. Plasma caffeine concentration before the first drink in the morning correlated very poorly with caffeine clearance (r2 = 0.07), even when adjusted for caffeine intake (r2 = 0.21).
测量了17名健康成年人在24小时内饮用的所有茶或咖啡饮品中的咖啡因含量。在相同的24小时内测定血浆中的咖啡因、茶碱、可可碱和副黄嘌呤浓度。速溶咖啡每杯的平均咖啡因含量为60.4±21.8毫克（范围为14倍），煮制咖啡为80.1±19.2毫克（范围为2.8倍），茶为28.8±13.7毫克（范围为5.5倍）。咖啡和茶的饮用量并不能很好地反映实际咖啡因摄入量（r2 = 0.42）。咖啡因摄入量与24小时平均咖啡因浓度的相关性较差（r2 = 0.41），但下午5点测得的单次血浆咖啡因浓度与24小时平均浓度之间存在非常好的相关性（r2 = 0.94）。副黄嘌呤的情况也是如此（r2 = 0.86）。副黄嘌呤占血浆中总二甲基黄嘌呤的67.3%，而可可碱和茶碱分别占24.4%和8.3%。平均咖啡因清除率为1.2±0.3毫升/分钟/千克。即使在根据咖啡因摄入量进行调整后（r2 = 0.21），早晨第一杯饮品前的血浆咖啡因浓度与咖啡因清除率的相关性仍很差（r2 = 0.07）。
