Does green tea protect against cancer?
Drinking green tea is safe and people who drink it develop cancer slightly less often, but whether the tea itself is the cause has not been proven. Do not regard green tea as protection against cancer.
Drinking green tea is associated with a slightly lower cancer risk: people who drink green tea develop cancer about 9% less often on average than people who do not. However, it has not been proven that the tea itself is responsible. Smoking, diet and other habits are linked to tea-drinking behaviour, and those are difficult to disentangle.
The strongest signal is for prostate cancer: in some studies, people who drink green tea develop it considerably less often, but the confidence interval is so wide that the true effect could be much smaller. Associations have also been found for oral cancer, gallbladder cancer and blood cancers, but the evidence there is likewise limited. For stomach cancer and colorectal cancer, studies contradict one another.
In the laboratory, the active compound EGCG inhibits and kills cancer cells without harming healthy ones. In animal studies, tumour suppression has been demonstrated at multiple sites. The caveat: those studies use quantities you could never obtain from tea. Those findings therefore do not translate straightforwardly to humans.
If you still want to try supplements, look for a product with 'green tea extract' or 'EGCG' on the label. In one safety study, volunteers received 2.25 g of extract (337.5 mg EGCG) per day for six months without serious side effects, but that is information, not a recommendation. Higher doses of EGCG have elsewhere been linked to liver toxicity. Always discuss supplements with your doctor before buying anything. How many cups of tea you would need to drink, and for how long, has not been established. Whether the brand, the origin or the form of the tea makes any difference cannot be determined from the available research.
This answer draws on one large summary of 36 population studies and 7 controlled trials, supplemented by several independent reviews of laboratory, animal and population research. The large summary found a statistically significant effect, but the researchers themselves pointed to considerable variation between studies, which limits reliability. The mechanistic evidence (laboratory and animal) is consistent, but the doses in animal experiments are much higher than what people realistically take in through tea. Evidence for a causal relationship in humans is currently lacking.
Does drinking coffee protect against liver cancer?
Drinking coffee is consistently associated with a lower risk of liver cancer, and that association is better supported than for most other cancer types. Three or more cups per day appears to give the strongest association, but if you are pregnant, keep your intake low and discuss it with your doctor.
Do lycopene and tomatoes protect against prostate cancer?
Processed tomato products are linked to a lower risk of prostate cancer, but whether lycopene is the cause is not certain. Lycopene supplements offer no proven benefit; simply eating more tomato sauce is the best-supported choice.
Is it true that artificial sweeteners cause cancer?
The vast majority of population research does not confirm a causal association between artificial sweeteners and cancer. There are signals around aspartame that are being investigated further, but these do not yet justify alarm.
Does eating less red meat lower your risk of cancer?
Eating less red meat and processed meat probably lowers your risk of colorectal cancer; the association is strongest and best supported for processed meat, so that is the first thing to cut back on.
Does taking vitamin D help against cancer?
If you already have sufficient vitamin D in your blood, extra supplementation probably does not help against cancer. If you have a demonstrable deficiency, have it corrected, but do not count on this significantly lowering your cancer risk.
Does eating from plastic packaging increase your risk of cancer?
Several large analyses show that chemicals in plastic packaging are associated with a higher risk of breast cancer. It has not yet been proven that they directly cause it.