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.
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
Optimal doses of black tea or its constituents are not known.
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.
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Last reviewed December 2015 by EBSCO CAM Review Board Last Updated: 12/15/2015