Green Tea Benefits

How should green tea benefits be read?

Green tea studies mix two different things: tea consumed as a beverage and the concentrated extract in capsules or tablets. NCCIH states that most of the cholesterol studies examined extract supplements rather than the beverage. ^[7] The effect in a meta-analysis therefore cannot be carried directly over to tea drunk daily. In addition, in observational studies, tea drinkers may also differ in lifestyle; an association does not mean tea caused it. Safety topics are in the main guide and the extract page: according to EFSA, EGCG at 800 mg per day and above as a supplement increased liver enzymes and no safe dose of EGCG could be established from extracts (extract page); tea can reduce iron absorption (iron guide).

Does green tea cause weight loss?

No, no clinically important weight loss has been shown. The Cochrane review (Jurgens et al., 2012) searched for randomized trials of at least 12 weeks comparing green tea preparations with control in overweight or obese adults; study durations are 12–13 weeks. In the meta-analysis of 6 studies outside Japan (532 participants), the mean weight difference was −0.04 kg (95% CI −0.5 to 0.4; p = 0.88). The 8 studies in Japan (1,030 participants) could not be pooled because they were dissimilar; they reported differences ranging from −0.2 to −3.5 kg in favor of green tea. For body mass index, the difference in studies outside Japan was −0.2 kg/m² (95% CI −0.5 to 0.1), and for waist circumference −0.2 cm (95% CI −1.4 to 0.9). Two studies (184 participants) examined maintenance of weight loss and found no significant effect. ^[1]

The authors’ conclusion is this: green tea preparations appear to produce a small, statistically nonsignificant weight loss in overweight or obese adults; because the loss is small, it is unlikely to be clinically important. No effect was found on weight maintenance. Four of the eight studies that recorded adverse events reported events; all but two were mild to moderate, and these two were in the green tea group, required hospitalization, and were reported in the studies as unrelated to the intervention. ^[1] The review was published in 2012; it covers searches made through December 2011 – January 2012 and does not include later studies.

Does green tea reduce the risk of cardiovascular disease?

In observational studies, green tea consumption was associated with lower cardiovascular death; this is not cause-and-effect evidence.

The Ohsaki study (Kuriyama et al., 2006). In a population-based, prospective cohort in Japan that began in 1994, 40,530 adults aged 40–79 without stroke, coronary heart disease, or cancer at baseline were followed. Follow-up was up to 11 years for all-cause mortality and up to 7 years for cause-specific mortality; 4,209 people died, 892 from cardiovascular disease and 1,134 from cancer. Green tea consumption was inversely associated with all-cause and cardiovascular mortality; for all-cause mortality the association was stronger in women (interaction with sex p = 0.03). In men, for all-cause mortality the hazard ratios relative to those drinking less than 1 cup per day were 0.93 (95% CI 0.83–1.05) for 1–2 cups, 0.95 (0.85–1.06) for 3–4 cups, and 0.88 (0.79–0.98) for 5 or more; in women, for the same categories, 0.98 (0.84–1.15), 0.82 (0.70–0.95), and 0.77 (0.67–0.89). In women, the hazard ratios for cardiovascular mortality across increasing consumption categories were 1.00, 0.84 (0.63–1.12), 0.69 (0.52–0.93), and 0.69 (0.53–0.90); among cardiovascular deaths, the strongest inverse association was seen for stroke death. For cancer death, the hazard ratios did not differ significantly from 1.00 in any category. ^[3]

NCCIH reports that green tea consumption has been associated with a lower risk of coronary heart disease in Asian populations and not in Western populations. ^[7] That is, the finding from Japan cannot be carried directly over to societies where green tea drinking habits are different.

Does green tea lower blood pressure?

A small decrease has been reported. Khalesi et al. (2014) pooled 13 randomized trials examining the effect of green tea catechins on blood pressure; articles were selected from 1995–2013. Compared with control, green tea lowered systolic blood pressure by 2.08 mmHg (95% CI −3.06 to −1.05) and diastolic blood pressure by 1.71 mmHg (95% CI −2.86 to −0.56). Subgroup analysis suggested a larger decrease in studies in which baseline systolic blood pressure was 130 mmHg and above and in studies in which tea was given as an extract. ^[4] These subgroup findings are not the main result; a mean decrease of 2 mmHg is a small effect and does not replace blood pressure treatment.

Does green tea lower cholesterol?

A small reduction in LDL cholesterol has been reported; there is no change in HDL. Khalesi et al. found a decrease of −0.15 mmol/L (95% CI −0.27 to −0.02) in total cholesterol and −0.16 mmol/L (95% CI −0.22 to −0.09) in LDL cholesterol. ^[4] Zheng et al. (2011) pooled 14 randomized trials (1,136 people) examining green tea beverage and extract; they found a decrease of 7.20 mg/dL (95% CI −8.19 to −6.21) in total cholesterol and 2.19 mg/dL (95% CI −3.16 to −1.21) in LDL, and no significant change in HDL. The authors report that the reduction did not vary with intervention type (beverage-extract), catechin dose, duration, and participant health status. ^[5] The LDL magnitudes of the two meta-analyses differ (about 6 mg/dL versus 2.19 mg/dL; the mmol/L–mg/dL conversion is a calculation). NCCIH also reports that green tea reduces total and LDL cholesterol to a small degree and does not affect HDL and triglycerides. ^[7]

Does green tea prevent cancer?

The evidence is inconsistent. The Cochrane review (Filippini et al., 2020) included 142 studies (11 experimental, 131 non-experimental). Eleven experimental studies assigned 1,795 participants to green tea extract or placebo. The summary risk ratio was 0.50 (95% CI 0.18–1.36; 3 studies, 201 participants) for prostate cancer, 1.50 (0.41–5.48; 2 studies, 1,157 participants) for gynecological cancer, and 1.00 (0.06–15.92; 1 study, 1,075 participants) for skin cancer (nonmelanoma); all three are of low certainty. Digestive disorders, increases in liver enzymes, and, more rarely, insomnia, increased blood pressure, and skin reactions were reported with the extracts. In observational studies (46 cohort and 85 case-control, more than 1,100,000 participants), comparing the highest and lowest green tea consumption, the RR was 0.83 (95% CI 0.65–1.07; 3 studies, 52,479 participants) for overall cancer incidence and 0.99 (0.91–1.07; 8 studies, 504,366 participants) for cancer-related death; both are of low certainty and the confidence intervals include 1.00. For some cancer types, cohort and case-control studies gave conflicting results. The authors state that results were inconsistent and that there is limited evidence of a benefit of green tea on cancer risk; most studies were conducted in Asian populations where green tea is heavily consumed. ^[2]

Does green tea prevent cognitive decline?

In observational studies, greater tea consumption is associated with a lower risk of cognitive impairment; the quality of the evidence is low to moderate. Quan et al. (2024), in searches through May 2022, pooled 23 cohort and 12 cross-sectional studies; the pooled risk ratios comparing the highest and lowest tea consumption categories were both in the direction of lower risk (95% CIs below 1). In the pooling of four randomized trials, the MMSE effect was 1.03 (95% CI 0.14–1.92). Green and black tea consumption was associated with a lower risk of cognitive impairment in eastern countries, especially in women. The authors state that the quality of the evidence is generally low to moderate. ^[6] This review examines not only green tea but different types of tea; the association does not mean tea protects cognition.

Summary of the evidence

This guide does not recommend personal doses. Because the products in the studies were beverages or extracts of differing composition, the finding of one study cannot be carried directly over to another product.