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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 2 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. 3 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. 4 Another study, about twice as large, failed to find benefit. 5 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), 8 lead to a more relaxed mental state, 9 and help reduce blood pressure . 10 Black tea might also help prevent cancer , though evidence from observational studies is thoroughly inconsistent. 11 12 13 14 Weak observational study evidence additionally hints at benefits for osteoporosis . 15 Though black tea has shown blood-sugar-lowering effects in healthy people, 16 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
References
- Hakim IA, Alsaif MA, Alduwaihy M, Al-Rubeaan K, Al-Nuaim AR, Al-Attas OS. Tea consumption and the prevalence of coronary heart disease in Saudi adults: results from a Saudi national study. Prev Med. 36(1):64-70.
- Vinson JA. Black and green tea and heart disease: a review. Biofactors. 13(1-4):127-32.
- Vinson JA, Teufel K, Wu N. Green and black teas inhibit atherosclerosis by lipid, antioxidant, and fibrinolytic mechanisms. J Agric Food Chem. 52(11):3661-5.
- Davies MJ, Judd JT, Baer DJ, Clevidence BA, Paul DR, Edwards AJ, Wiseman SA, Muesing RA, Chen SC. Black tea consumption reduces total and LDL cholesterol in mildly hypercholesterolemic adults. J Nutr. 133(10):3298S-3302S.
- Mukamal KJ, MacDermott K, Vinson JA, Oyama N, Manning WJ, Mittleman MA. A 6-month randomized pilot study of black tea and cardiovascular risk factors. Am Heart J. 154(4):724.e1-6.
- Maron DJ, Lu GP, Cai NS, Wu ZG, Li YH, Chen H, Zhu JQ, Jin XJ, Wouters BC, Zhao J. Cholesterol-lowering effect of a theaflavin-enriched green tea extract: a randomized controlled trial. Arch Intern Med. 163(12):1448-53.
- Kraemer WJ, French DN, Spiering BA, Volek JS, Sharman MJ, Ratamess NA, Judelson DA, Silvestre R, Watson G, Gómez A, Maresh CM. Cortitrol supplementation reduces serum cortisol responses to physical stress. Metabolism. 54(5):657-68.
- Kimura K, Ozeki M, Juneja LR, Ohira H. L-Theanine reduces psychological and physiological stress responses. Biol Psychol. 74(1):39-45.
- Nobre AC, Rao A, Owen GN. L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pac J Clin Nutr. 17 Suppl 1():167-8.
- Rogers PJ, Smith JE, Heatherley SV, Pleydell-Pearce CW. Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together. Psychopharmacology (Berl). 195(4):569-77.
- Blot WJ, McLaughlin JK, Chow WH. Cancer rates among drinkers of black tea. Crit Rev Food Sci Nutr. 37(8):739-60.
- Hartman TJ, Tangrea JA, Pietinen P, Malila N, Virtanen M, Taylor PR, Albanes D. Tea and coffee consumption and risk of colon and rectal cancer in middle-aged Finnish men. Nutr Cancer. 31(1):41-8.
- Mukhtar H, Ahmad N. Tea polyphenols: prevention of cancer and optimizing health. Am J Clin Nutr. 71(6 Suppl):1698S-702S; discussion 1703S-4S.
- Wu AH, Yu MC, Tseng CC, Hankin J, Pike MC. Green tea and risk of breast cancer in Asian Americans. Int J Cancer. 106(4):574-9.
- Hegarty VM, May HM, Khaw KT. Tea drinking and bone mineral density in older women. Am J Clin Nutr. 71(4):1003-7.
- 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. 26(5):471-7.
- 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. 56(10):1340-4.
