Caffeine is a natural chemical found in such items as tea leaves and coffee beans. Caffeine research has received intensive attention from scientists and food/beverage industries.
In a report of the safety of dietary caffeine in 1981, the American Medical Association Council on Science suggested that “moderate tea or coffee drinkers probably need have no concern for their health relative to their caffeine consumption provided other life-style habits (diet, alcohol consumption) are moderate, as well.” 
Moreover, the Harvard School of Public Health (HSPH) suggests that moderate caffeine consumption may have some beneficial healthy effects, as found in some scientific studies , including potential effects against type 2 diabetes , reduction risk of coronary heart disease , etc. According to the HSPH’s healthy beverage guidelines, up to three or four cups of coffee or tea per day appear to be fine for healthy adults .
Similarly, in 2008, the International Food Information Council Foundation (IFIC Foundation) provided a comprehensive update on the research on caffeine and health in a report titled “Caffeine & Health: Clarifying the Controversies.” The IFIC suggests in the report, “For the healthy adult population, moderatecaffeine consumption of 300 mg per day is safe and can even have beneficial health implications as a part of a healthful diet and physically active lifestyle” . The report discussed potential benefits of moderate caffeine consumption on mental and physical performance, and its potential to reduce risks of Diabetes, Parkinson’s, and other diseases. In particular, both IFIC  and HSPH  resources point out that pregnant women, children, older individuals, and people with a history of heart disease should be careful with their caffeine intake and consult with a doctor.
Caffeine and Tea
All teas contain caffeine unless they are intentionally decaffeinated during processing. According to the USDA National Nutrient Database (2010, Release 23), a cup of black tea contains about half as much caffeine as a cup of coffee (47mg caffeine in tea vs. 95mg in coffee per 8oz cup) . The HSPH’s caffeine comparison  determined that the caffeine amount in three cups of generic brewed coffee equals the caffeine amount in seven cups of tea. Click here to see more caffeine comparisons from Harvard School of Public Health.
Black tea generally has more caffeine than teas that are less or non-oxidized. Thus, green, white, and oolong teas have less caffeine than black tea. Additionally, caffeine content may vary based on brewing time, the amount of tea, and whether the tea is loose or in teabags, etc. . The longer the steeping time and the more amount of loose tea leaves, the more caffeine in tea.
Health&Tea — Caffeine Level of our Teas
Milligram of caffeine per 8 fl. oz cup brewed with 2.5 grams of tea. Analysis conducted by a third party independent lab.
Linus Pauling Institute summarized the caffeine content from several tea studies and offers general information about caffeine content, as shown in the table below . It further notes that the caffeine content of oolong teas is comparable to green teas . White teas are often grouped together with green, though some white teas might have slightly higher caffeine levels because their young tea leaves and buds have higher caffeine content .
Summarized by Linus Pauling Institute, Oregon State University
- Caffeine Labeling, Council on Scientific Affairs, Division of Personal and Public Health Policy, American Medical Association, JAMA. 1984;252(6):803-806, [Excerpt]
- Coffee: The Good News, Harvard School of Public Health, http://www.hsph.harvard.edu/multimedia/flash/2010/coffee/benefits.html(May 2011).
- Huxley, R., Lee, C.M., Barzi, F., Timmermeister, L., Czernichow, S., Perkovic, V., Grobbee, D.E., Batty, D., Woodward, M., 2009, Coffee, decaffeinated coffee, and tea consumption in relation to incident type 2 diabetes mellitus: a systematic review with meta-analysis, Arch Intern Med.2009 Dec 14;169(22):2053-63, [Abstract]
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- Healthy Beverage Guidelines, Harvard School of Public Health, http://www.hsph.harvard.edu/nutritionsource/healthy-drinks/healthy-drinks-full-story/, (May 2011)
- IFIC Review, Caffeine and Health: Clarifying The Controversies, 2008, [Pdf], (May 2011)
- Van Dam, R., The Nutrition Source, Ask the Expert: Coffee and Health, http://www.hsph.harvard.edu/nutritionsource/questions/coffee/(May 2011)
- USDA National Nutrient Database for Standard Reference, Release 23. 2010, http://www.nal.usda.gov/fnic/foodcomp/search/(May 2011).
- Caffeine Comparisons, Harvard School of Public Health, [Link] (May 2011).
- Tea Summary, Micronutrient Research for Optimum Health, Linus Pauling Institue, Oregon State Univeristy, http://lpi.oregonstate.edu/infocenter/phytochemicals/tea/ (May 2011).
- Lin JK, Lin CL, Liang YC, Lin-Shiau SY, Juan IM. Survey of catechins, gallic acid, and methylxanthines in green, oolong, pu-erh, and black teas. J Agric Food Chem. 1998;46(9):3635-3642. [Abstract]
- Santana-Rios, G., Orner, G.A., Amantana, A., Provost, C., Wu, S.Y., Dashwood RH. Potent antimutagenic activity of white tea in comparison with green tea in the Salmonella assay. Mutat Res. 2001;495(1-2):61-74. [Abstract]