Stavric B, Klassen R, Watkinson B, Karpinski K, Stapley R, Fried P
Food Research Division, Bureau of Chemical Safety, Ottawa, Ontario, Canada.
Food Chem Toxicol. 1988 Feb;26(2):111-8. doi: 10.1016/0278-6915(88)90107-x.
Five surveys, using a previously developed high-performance liquid chromatography procedure to measure caffeine concentrations, indicated great variations in the concentrations of caffeine in tea and coffee. In the study of beverages prepared at home, data on caffeine concentrations in 58 samples of tea and coffee, volumes of cups, and numbers of cups consumed/day, indicated that the range of caffeine intakes for the women participating was 49-1022 mg/day. There were considerable day-to-day variations in caffeine contents in coffee samples from some commercial coffee shops. When 17 samples of five national brands of instant coffee were made into beverages in the laboratory, variations in caffeine concentrations between lots were small but between brands were significant. A considerable range of caffeine concentrations was also found when 12 samples of coffee prepared at work by different individuals using the same jar of instant coffee were analysed. Analysis of tea samples prepared in the laboratory indicated that steeping time had an important influence on resulting caffeine and theobromine concentrations. People preparing their own beverages were found to drink more liquid than the volume offered commerically. The mean caffeine 'contents' of home-made coffee and of coffee prepared by individuals at work were 79.4 and 81.7 mg/cup respectively, indicating a mean intake of approximately 80 mg caffeine/cup. When this amount (80 mg/cup) was used to estimate daily intakes of caffeine from coffee, on the basis of the number of reported cups/day, and the values obtained were compared with the amounts actually consumed by individuals, the potential for misrepresentation of individual consumption became obvious. For example, for subjects consuming three cups of coffee, only 25% would have been correctly categorized in the expected range for the daily intake of caffeine, 39% would have been overestimated and 36% underestimated for the amount of caffeine consumed. These variations in caffeine concentrations and in the volume of coffee consumed have frequently been ignored in examinations of the possible relationship between coffee consumption and various health problems, and this could perhaps partly explain some conflicting results seen in epidemiological studies.
五项调查采用先前开发的高效液相色谱法来测量咖啡因浓度，结果表明茶和咖啡中的咖啡因浓度存在很大差异。在对家庭自制饮品的研究中，关于58份茶和咖啡样本中的咖啡因浓度、杯子容量以及每天饮用杯数的数据表明，参与研究的女性咖啡因摄入量范围为49 - 1022毫克/天。一些商业咖啡店的咖啡样本中，咖啡因含量存在相当大的每日波动。当在实验室将五个国产品牌速溶咖啡的17个样本制成饮品时，批次间咖啡因浓度的差异较小，但品牌间差异显著。对不同人使用同一罐速溶咖啡在工作场所冲泡的12份咖啡样本进行分析时，也发现了相当大的咖啡因浓度范围。实验室对茶样本的分析表明，浸泡时间对最终的咖啡因和可可碱浓度有重要影响。发现自制饮品的人饮用的液体量比商业提供的量更多。自制咖啡和个人在工作场所冲泡的咖啡的平均咖啡因“含量”分别为79.4毫克/杯和81.7毫克/杯，这表明平均摄入量约为80毫克咖啡因/杯。当以这个量（80毫克/杯）根据报告的每日杯数来估算咖啡的每日咖啡因摄入量，并将所得值与个人实际摄入量进行比较时，个人摄入量被误判的可能性就变得明显了。例如，对于饮用三杯咖啡的受试者，只有25%的人会被正确归类到预期的每日咖啡因摄入量范围内，39%的人摄入量被高估，36%的人摄入量被低估。在研究咖啡消费与各种健康问题之间可能存在的关系时，咖啡因浓度和咖啡饮用量的这些差异常常被忽视，这或许可以部分解释流行病学研究中出现的一些相互矛盾的结果。
