Benefits
Cholesterol Levels
In a 12-week trial, a theaflavin-enriched green tea extract lowered LDL cholesterol by 16.4% in adults with raised cholesterol on a low-fat diet. A later 11-week trial found that neither purified theaflavins nor a similar theaflavin and catechin blend lowered total or LDL cholesterol versus placebo. Pooled black tea trials show an LDL drop of about 5 mg/dL at most, so the results are mixed.
Antioxidant Activity
Theaflavins are studied as antioxidants mainly in laboratory and animal research. The only human antioxidant data come from a 12-week trial of three cups of black tea a day, in which a blood antioxidant-capacity marker (FRAP) rose. That tea contained many polyphenols besides theaflavins, and the marker is a laboratory measure rather than a health outcome.
Cholesterol Absorption (Laboratory and Animal Research)
A review of laboratory and animal research reports that theaflavins block the formation of the micelles that carry cholesterol in the gut, which would reduce cholesterol absorption. Human trials of theaflavin products have not shown consistent cholesterol lowering, so this effect is not confirmed in people.
Inflammation Pathways (Laboratory and Animal Research)
A review of laboratory and animal research reports that theaflavins inhibit inflammation as part of how they improved insulin sensitivity in animals. No human trial cited here measured inflammation after theaflavins, so this effect has not been shown in people.
Mechanism of action
Cholesterol Absorption Reduction
In laboratory and animal research, theaflavins block the formation of micelles, the tiny particles that carry cholesterol in the gut, which would reduce cholesterol absorption. Human trials of theaflavin products have not shown consistent cholesterol lowering.
Antioxidant Signaling (Animal Research)
A review of animal research reports that theaflavins switch on Nrf2 signaling, a cell pathway that controls antioxidant defenses, in work on atherosclerosis. In people, the only antioxidant data come from one black tea trial in which a blood antioxidant marker rose.
Other Metabolic Pathways (Animal Research)
In laboratory and animal studies, theaflavins inhibited pancreatic lipase, an enzyme that digests fat, activated AMPK, an energy-sensing enzyme, and changed the gut microbiota. These findings have not been confirmed in people.
Clinical trials
Double-blind, randomized, placebo-controlled, parallel-group trial in outpatient clinics of 6 urban hospitals in China: a daily capsule of theaflavin-enriched green tea extract (375 mg, with 75 mg theaflavins, 150 mg catechins and 150 mg other tea polyphenols) or placebo for 12 weeks, alongside a low-fat diet. The extract's supplier, Nashai Biotech, sponsored the study, and two authors were company officers. (Maron et al. 2003, Arch Intern Med)
240 men and women aged 18 or older with mild to moderate high cholesterol, on a low-fat diet; all were Asian, and 220 completed the trial.
In the tea extract group, total cholesterol fell 11.3% and LDL cholesterol 16.4% from baseline (both P=0.01); HDL cholesterol and triglycerides did not change significantly, and the placebo group showed no significant changes. No significant adverse events were seen. The extract also contained catechins and other polyphenols, so the effect cannot be credited to theaflavins alone.
Systematic review and meta-analysis of randomized controlled trials of regular black tea drinking and serum cholesterol, searched in PubMed, Scopus and the Cochrane Library following PRISMA. (Zhao et al. 2015, Clin Nutr)
10 trials with 411 participants in total.
Black tea lowered LDL cholesterol by 4.64 mg/dL (95% CI -8.99 to -0.30, p=0.036) with no significant heterogeneity. Total cholesterol (-2.04 mg/dL) and HDL cholesterol did not change significantly. The LDL drop was larger in people at higher cardiovascular risk. The tea was a whole-tea blend, not purified theaflavins.
Randomized, double-blind, placebo-controlled, parallel trial. One daily capsule of purified black tea theaflavins (77.5 mg), theaflavins plus catechins (75 mg theaflavins, 150 mg catechins, 195 mg other polyphenols) or placebo (cellulose) for 11 weeks. The lead author was from Unilever Research and Development. (Trautwein et al. 2010, Eur J Nutr)
102 adults (67 men, 35 women) with mildly to moderately raised total and LDL cholesterol.
Total and LDL cholesterol did not differ among the three groups at 4, 8 or 11 weeks (p=0.1187 and p=0.1063). Cholesterol fell slightly over time, but this happened in the theaflavin and placebo groups alike. The authors concluded that neither theaflavins alone nor the theaflavin and catechin blend lowered LDL cholesterol at these doses.
Meta-analysis of 15 randomized controlled trials of black tea and blood cholesterol, using fixed-effects and random-effects models plus meta-regression for polyphenol dose. (Wang et al. 2014, PLoS One)
Healthy adults and patients with coronary artery disease across 15 randomized trials.
Black tea did not significantly lower total cholesterol or change HDL cholesterol. In healthy participants LDL fell by 5.57 mg/dL in the fixed-effects model (p=0.005) but not significantly in the random-effects model (-4.56 mg/dL, p=0.12). LDL did not change in patients with coronary artery disease, and no dose effect of black tea polyphenols was found. The authors concluded black tea might not benefit cholesterol.