Summary of findings 1. Green tea extract supplementation compared with placebo for preventing cancer: experimental studies.

Green tea extract supplementation compared with placebo for cancer prevention: experimental studies
Patient or population: adults (aged at least 18 years) Settings: outpatients Intervention: green tea extract supplementation Comparison: placebo
Outcomes	Relative effect (95% CI)	Anticipated absolute effects* (95% CI) (studies)			No of participants (studies)	Certainty of the evidence (GRADE)	Comments/explanations
		Placebo	Green tea extract supplementation	Difference
Prostate cancer incidence	RR 0.50 (0.18 to 1.36)	22.0%	11.7% (4.4 to 28.7)	10.3% fewer (17.6 fewer to 6.7 more)	201 (3 RCTs)	⊕⊕⊝⊝ Low	Very large effects, but all participants were at high risk of prostate cancer at the time of recruitment, with high‐grade prostatic intraepithelial neoplasia and/or atypical small acinar proliferation less than 3 months before, thus the indirectness in transferring the results to the general population, high imprecision of the summary estimates based on only 201 participants and 32 cases, and high inconsistency between study results
Gynaecological cancer incidence	RR 1.50 (0.41 to 5.48)	0.9%	1.3% (0.4 to 4.6)	0.4% more (0.5 fewer to 3.7 more)	1157 (2 RCTs)	⊕⊕⊝⊝ Low	Large effects, but high imprecision of the summary RR and high inconsistency of results due to contradictory findings from two available studies.
Non‐melanoma skin cancer incidence	RR 1.00 (0.06 to 15.92)	0.2%	0.2% (0.0 to 2.9)	0.0% fewer (0.0 fewer to 2.7 more)	1075 (1 RCT)	⊕⊕⊝⊝ Low	Very high imprecision based on only one study and no large effect detected.
Quality of life	Not estimable	‐	‐	‐	‐	Not assessed	Due to the large number of different scales used it was not possible to the overall certainty of evidence.
The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; RCT: randomised controlled trial; RR: risk ratio
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect.