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Black Tea

Alternate Names/Related terms

  • Theanine

Black and green tea are made from the same plant, but black tea has been allowed to oxidize, altering its constituents. While green tea is high in catechins (especially epigallocatechin gallate, or EGCG), black tea contains relatively high levels of theaflavins, theanine, and thearubigens. Although green tea is more commonly presented as a healthful beverage, traditional black tea too might have health-promoting properties. However, there is no reliable evidence as yet for any of its proposed health benefits.

What Is Black Tea Used for Today?

According to some but not all observational studies , high consumption of black tea is associated with reduced risk of heart disease and heart disease death. 1-3

Unfortunately, observational studies are notoriously unreliable for proving the efficacy of a treatment. Some additional support comes from animal studies that hint black tea may help prevent atherosclerosis , the primary cause of heart disease. 4 However, only double-blind , placebo-controlled studies can actually prove a treatment effective, and few have been conducted on black tea. (For information about why such studies are essential, see Why Does This Database Rely on Double-blind Studies? ) One double-blind, placebo-controlled study found that black tea modestly improves cholesterol profile, but it enrolled too few participants (a total of 15) to provide trustworthy results. 5 Another study, about twice as large, failed to find benefit. 18

A much larger study (more than 200 participants) evaluated a form of green tea enriched with black tea theaflavin. 6 In this substantial 3-month study, use of the tea product resulted in significant reductions in LDL ("bad") cholesterol as compared to placebo. However, these results might not apply to black tea itself.

Theanine, a component of black tea, has been advocated as a sports supplement . Physical activity causes elevation of the stress hormone cortisol, which could, in theory, interfere with the benefits of exercise by slowing muscle growth. One study widely reported by tea advocates tested a mixture of theanine and several other herbs and supplements ( Magnolia officinalis , Epimedium koreanum , beta-sitosterol , and phosphatidylserine ). 7 The results appeared to indicate that use of this combination could decrease the cortisol response to exercise, and on this basis, theanine and the combination supplement are widely marketed as an aid to body building. However, this study suffers from a number of limitations. Perhaps the most important of these limitations is that presumably the body releases cortisol during exercise for a reason, and preventing this response may not, in fact, produce health benefits. In addition, the study was not designed to look for particular benefits, such as improved muscle development.

Other preliminary evidence from small trials suggests that the consumption of theanine in black tea may reduce the body's response to stress in general (physical or psychological), 15,16 lead to a more relaxed mental state, 21 and help reduce blood pressure . 19,24

Black tea might also help prevent cancer , though evidence from observational studies is thoroughly inconsistent. 8-12 Weak observational study evidence additionally hints at benefits for osteoporosis . 13

Though black tea has shown blood-sugar-lowering effects in healthy people, 20 one study failed to find that a combined extract of black and green tea could help control blood sugar levels in people with type 2 diabetes . 17

Suntheanine, a supplement that contains L-theanine, showed some promise in improving sleep quality in boys with attention deficit hyperactivity disorder (ADHD). 23


Optimal doses of black tea or its constituents are not known.

Safety Issues

As an extraordinarily widely consumed beverage, black tea is presumed to have a high safety factor. Its side effects would be expected to be similar to those of coffee—heartburn, gastritis, insomnia, anxiety, and heart arrhythmias (benign palpitations or more serious disturbances of heart rhythm). 14 All drug interactions that can occur with caffeine would be expected to occur with black tea.

Interactions You Should Know About

If you are taking:

  • MAO inhibitors : The caffeine in black tea could cause dangerous drug interactions.
  • Stimulant drugs such as Ritalin: The stimulant effects of black tea might be amplified.
  • Drugs to prevent heart arrhythmias or to treat insomnia , heartburn , ulcers , or anxiety : Black tea might interfere with their action.
  • Folic acid : Black tea may decrease the absorption of folic acid into the blood stream. 22

Revision Information

  • 1

    Hakim IA, Alsaif MA, Alduwaihy M, et al. Tea consumption and the prevalence of coronary heart disease in Saudi adults: results from a Saudi national study. Prev Med . 2002;36:64-70.

  • 2

    Vinson JA. Black and green tea and heart disease: a review. Biofactors . 2001;13:127-132.

  • 3

    Sesso HD, Paffenbarger RS Jr, Oguma Y, et al. Lack of association between tea and cardiovascular disease in college alumni. Int J Epidemiol . 2003;32:527-533.

  • 4

    Vinson JA, Teufel K, Wu N, et al. Green and black teas inhibit atherosclerosis by lipid, antioxidant, and fibrinolytic mechanisms. J Agric Food Chem . 2004;52:3661-3665.

  • 5

    Davies MJ, Judd JT, Baer DJ, et al. Black tea consumption reduces total and LDL cholesterol in mildly hypercholesterolemic adults. J Nutr . 2003;133:3298S-3302S.

  • 6

    Maron DJ, Lu GP, Cai NS, et al. Cholesterol-lowering effect of a theaflavin-enriched green tea extract: a randomized controlled trial. Arch Intern Med . 2003;163:1448-1453.

  • 7

    Kraemer WJ, French DN, Spiering BA, et al. Cortitrol supplementation reduces serum cortisol responses to physical stress. Metabolism . 2005;54:657-668.

  • 8

    Blot WJ, McLaughlin JK, Chow WH, et al. Cancer rates among drinkers of black tea. Crit Rev Food Sci Nutr . 1998;37:739-760.

  • 9

    Hartman TJ, Tangrea JA, Pietinen P, et al. Tea and coffee consumption and risk of colon and rectal cancer in middle-aged Finnish men. Nutr Cancer . 1998;31:41-48.

  • 10

    Mukhtar H, Ahmad N. Tea polyphenols: prevention of cancer and optimizing health. Am J Clin Nutr . 2000;71:1698S-1702S; discussion 1703S-4S.

  • 11

    Wu AH, Yu MC, Tseng CC, et al. Green tea and risk of breast cancer in Asian Americans. Int J Cancer . 2003;106:574-579.

  • 12

    Arab L, Il'yasova D. The epidemiology of tea consumption and colorectal cancer incidence. J Nutr . 2003;133:3310S-3318S.

  • 13

    Hegarty VM, May HM, Khaw KT. Tea drinking and bone mineral density in older women. Am J Clin Nutr . 2000;71:1003-1007.

  • 14

    Cannon ME, Cooke CT, McCarthy JS. Caffeine-induced cardiac arrhythmia: an unrecognised danger of healthfood products. Med J Aust. 2001;174:520-521.

  • 15

    Kimura K, Ozeki M, Juneja LR, et al. L-Theanine reduces psychological and physiological stress responses. Biol Psychol. 2006 Aug 21. [Epub ahead of print]

  • 16

    Kraemer WJ, French DN, Spiering BA, et al. Cortitrol supplementation reduces serum cortisol responses to physical stress. Metabolism . 2005;54:657-668.

  • 17

    Mackenzie T, Leary L, Brooks WB. The effect of an extract of green and black tea on glucose control in adults with type 2 diabetes mellitus: double-blind randomized study. Metabolism. 2007;56:1340-1344.

  • 18

    Mukamal KJ, MacDermott K, Vinson JA, et al. A 6-month randomized pilot study of black tea and cardiovascular risk factors. Am Heart J. 2007;154:724.e1-6.

  • 19

    Rogers PJ, Smith JE, Heatherley SV, et al. Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together. Psychopharmacology (Berl). 2007 Sep 23. [Epub ahead of print]

  • 20

    Bryans JA, Judd PA, Ellis PR. The effect of consuming instant black tea on postprandial plasma glucose and insulin concentrations in healthy humans. J Am Coll Nutr. 2007;26:471-477.

  • 21

    Nobre AC, Rao A, Owen GN. L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pac J Clin Nutr. 2008;17(suppl 1):167-168.

  • 22

    Alemdaroglu NC, Dietz U, Wolffram S, et al. Influence of green and black tea on folic acid pharmacokinetics in healthy volunteers: potential risk of diminished folic acid bioavailability. Biopharm Drug Dispos. 2008 Jun 12.

  • 23

    Lyon MR, Kapoor MP, Juneja LR. The effects of L-theanine (Suntheanine) on objective sleep quality in boys with attention deficit hyperactivity disorder (ADHD): a randomized, double-blind, placebo-controlled clinical trial. Altern Med Rev. 2011;16(4):348-354.

  • 24

    Hodgson JM, Puddey IB, Woodman RJ, et al. Effects of black tea on blood pressure: a randomized controlled trial. Arch Intern Med. 2012;172(2):186-188.