Black Tea (Camellia sinensis, Theanine)
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.
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.
Some additional support comes from animal studies that hint black tea may help prevent atherosclerosis, the primary cause of heart disease. 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.
A much larger study (over 200 participants) evaluated a form of green tea enriched with black tea theaflavin. 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 reported by tea advocates tested a mixture of theanine and several other herbs and supplements (Magnolia officinalis, Epimedium koreanum, beta-sitosterol, and phosphatidylserine).
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 evidence from small trials suggests that theanine may reduce the body's response to stress in general (physical or psychological).
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.
Dosage
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 arrythmias (benign palpitations or more serious disturbances of heart rhythm). All drug interactions that can occur with caffeine would be expected to occur with black tea.
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