Does drinking green tea protect your heart?

Green tea leaves contain several types of catechins, but epigallocatechin gallate (EGCG) is the most abundant. In laboratory studies, catechins act as antioxidants by scavenging free radicals, chelating redox-active metal ions, and inducing the body's own antioxidant enzymes¹. Beyond antioxidant activity, they influence inflammation, blood vessel tone, and fat metabolism in cell and animal experiments^1,6.

Cardiovascular protection

A large prospective study in Japan following 40,530 adults found that green tea consumption was inversely associated with death from cardiovascular disease and from all causes. In women, those who drank five or more cups a day had a hazard ratio of 0.69 (95% CI 0.53-0.90) for cardiovascular mortality compared with those who drank less than one cup, and the strongest association was with stroke mortality². The proposed mechanisms include regulation of vascular tone through endothelial nitric oxide, antioxidant and lipid-lowering effects, and suppression of platelet adhesion¹.

Metabolic and weight management

Reviews list body-weight control among the possible benefits of green tea⁴, and a 2007 review concluded that regular intake of about 5-6 or more cups a day, or a green tea product supplying 200-300 mg of EGCG, was associated with cardiovascular and metabolic benefits in epidemiological and intervention studies⁶. The same review stressed that proving a benefit for disease prevention or treatment would require long-term, multi-center trials of one precisely defined green tea product⁶.

Cancer prevention research

Early research on green tea and EGCG focused on cancer, with encouraging data from cell, animal, and human studies⁶, and one review suggests green tea may contribute to a lower risk of some forms of cancer⁴. But the strongest human data are not clear-cut: in the Ohsaki cohort, green tea consumption was not associated with lower cancer mortality, even though it was associated with lower cardiovascular and all-cause mortality².

Improving catechin absorption

Green tea catechins are unstable under digestive conditions: in a simulated gastric and intestinal digestion, less than 20% of total catechins, and less than 10% of EGCG and EGC, survived. Adding 30 mg of vitamin C (ascorbic acid) to 250 mL of tea raised the recovery of EGCG to 54% and of EGC to 74%, and citrus juices (orange, grapefruit, lemon, and lime) gave even higher recoveries of EGCG, 56-76%⁵. In rats, a green tea formulated with ascorbic acid and sucrose produced roughly three times the blood exposure to EGCG of plain tea⁷. Whether the same happens in people has not been shown.

Cardiovascular outcomes

The most cited epidemiological evidence comes from the Ohsaki National Health Insurance Cohort Study (n = 40,530; adults aged 40-79 without a history of stroke, coronary heart disease, or cancer). Kuriyama et al. (2006) followed participants for up to 11 years for all-cause mortality and up to 7 years for cause-specific mortality². Over 11 years 4,209 participants died; over the 7-year cause-specific follow-up, 892 died of cardiovascular disease and 1,134 of cancer. Green tea consumption was inversely associated with all-cause and cardiovascular mortality. In men, the hazard ratio of all-cause mortality was 0.88 (95% CI 0.79-0.98) for five or more cups a day compared with less than one cup; in women it was 0.77 (0.67-0.89). The inverse association with cardiovascular mortality was stronger than that with all-cause mortality and stronger in women (hazard ratio 0.69, 95% CI 0.53-0.90, for five or more cups a day). Among types of cardiovascular death, the strongest inverse association was for stroke. Hazard ratios for cancer mortality were not significantly different from 1.00 in any green tea category.

Babu and Liu (2008) reviewed the mechanistic evidence for green tea catechins and vascular health and described several routes by which catechins protect blood vessels¹. They scavenge free radicals and chelate redox-active metals; they inhibit key enzymes of lipid biosynthesis and reduce intestinal lipid absorption, which improves blood lipids; they regulate vascular tone by activating endothelial nitric oxide; they suppress vascular inflammation by inhibiting NF-kB-mediated production of cytokines and adhesion molecules; they inhibit proliferation of vascular smooth muscle cells; and they suppress platelet adhesion, thereby inhibiting thrombogenesis. The review concludes that catechins may be novel plant-derived small molecules for preventing and treating cardiovascular disease, but the evidence it describes combines epidemiological, clinical, and experimental studies.

Wolfram (2007) reviewed the research on green tea and EGCG for cardiovascular and metabolic health⁶. Dose-response relationships in several epidemiological studies indicated that pronounced cardiovascular and metabolic benefits could be obtained by regular consumption of 5-6 or more cups of green tea per day, and intervention studies using similar amounts of green tea (200-300 mg of EGCG) supported its usefulness for maintaining cardiovascular and metabolic health. The review called for several multi-center, long-term clinical studies of one precisely defined green tea product to prove effectiveness for disease prevention or treatment.

Neuroprotection and aging

Prasanth et al. (2019) reviewed green tea's effects on photoaging, stress resistance, neuroprotection, and autophagy³. Several in vivo and in vitro studies suggest that green tea supplementation increases collagen and elastin content in the skin and suppresses the collagen-degrading enzyme MMP-3, which may confer an anti-wrinkle effect. Studies in worms suggest that green tea-mediated lifespan extension depends on the DAF-16 pathway. Green tea has also been reported to have stress-resistance and neuroprotective properties; EGCG was found to suppress amyloid-beta-induced neurotoxicity in experimental models, and green tea polyphenols induce autophagy. The review notes that the precise mechanism of the anti-photoaging effect has not been explored. These are laboratory and animal findings, and the review does not establish benefit in people.

Bioavailability considerations

Green et al. (2007) measured how common additives affect the recovery of green tea catechins after simulated gastric and small-intestinal digestion⁵. Without additives, less than 20% of total catechins remained after digestion, and EGC and EGCG were most sensitive, with less than 10% recovery. Teas formulated with 50% bovine, soy, or rice milk raised total catechin recovery to 52%, 55%, and 69%. Including 30 mg of ascorbic acid in 250 mL of tea significantly increased the recovery of EGC, EGCG, EC, and ECG to 74%, 54%, 82%, and 45%, and juice preparations gave the highest recovery of any formulation: EGC 81-98%, EGCG 56-76%, EC 86-95%, and ECG 30-55%. This was an in vitro digestion experiment, so it shows what survives digestion, not what is absorbed into the blood.

Peters et al. (2010) tested a green tea extract formulated plain, with sucrose, with ascorbic acid, and with both, using rats and a Caco-2 intestinal cell model⁷. The absorption of EGC and EGCG was significantly enhanced with sucrose plus ascorbic acid: the area under the curve for EGCG was 181.8 pmol*h/L versus 61.0 for plain tea, and for EGC 3,237 versus 1,304. Caco-2 cells accumulated more EGC, EGCG, and ECG from the sucrose-plus-ascorbic-acid formulation. The authors concluded that this formulation may improve catechin bioavailability, but that is an animal and cell finding.

Summary of the evidence

Cabrera et al. (2006) reviewed the broader literature⁴. They noted that catechins are strong antioxidants in vitro and in vivo, that recent human studies suggest green tea may contribute to a reduction in the risk of cardiovascular disease and some forms of cancer, and that it has been linked to other functions including antihypertensive effects, body-weight control, and bone mineral density. They concluded that, although the evidence is very promising, further studies are needed to understand its contribution to human health before regular consumption can be advised in Western diets. Taken with the Ohsaki cohort², the strongest human evidence is observational and points to lower cardiovascular and all-cause mortality among habitual drinkers in Japan, with no clear effect on cancer mortality.