What is green tea? Does green tea extract work in cancer treatment?

Green tea, a beverage native to Asian countries, has also begun to be widely consumed in our country. Although the first question about this herbal product is whether green tea helps weight loss, its effects on cancer are also of interest and have been the subject of many studies.

Its scientific name is Camellia sinensis , and green tea is grown mainly in China and other Asian countries. Its history dates back to 3000 BC. Although claimed benefits include lowering blood pressure and cholesterol and helping weight loss, there are not enough studies in these areas.

When researching green tea on Google’, we see that the most frequent questions are: does green tea help weight loss, how to brew green tea, harms of green tea, how much green tea to drink, green tea mineral water regimen … As this shows, society perceives green tea as a beneficial alternative medicine product , but also suspects it may be harmful. This suspicion is justified, because many cases of acute—sudden-onset—liver damage, liver failure and even death have occurred, particularly after heavy green tea consumption.

Scientific studies of green tea have recently focused on its effect in cancer treatment. Various studies have examined the effects on cancer of polyphenol compounds in green tea extract, such as flavonoids, catechins and tannins. The most researched substance in green tea is a catechin, Epigallocatechin Gallate (EGCG = epigallocatechin gallate).

Supportive studies

• In patients receiving radiotherapy to any of the head, neck or abdominal areas, green tea compresses were applied to the treated skin three times daily for ten minutes. These skin areas were subsequently observed to be less affected by radiotherapy.
• A phase 1 study in postmenopausal women of Caucasian origin found that green tea use might generally be safe for cancer patients and individuals at risk of cancer. The same study also observed that green tea reduced diarrhea . 
• Various studies observed that consuming 7 cups of green tea or Epigallocatechin Gallate daily might reduce the risk of prostate, liver and endometrial (uterine) cancer. However, heavy green tea consumption also carries a risk of liver damage. Therefore, certain green tea extract products used particularly for weight loss were banned in Spain and France in 2003.
• A laboratory study found that green tea polyphenol compounds (GTP) could activate the immune system. In the same study, high amounts of these compounds suppressed tumor progression in animal models. However, this study is insufficient to demonstrate that green tea suppresses tumor progression.
• Another study aims to prevent prostate cancer through the use of GTP molecules together with nanotechnology .
• Various laboratory studies found that catechin types in green tea (GTC) suppress breast cancer cells. However, the amount of GTC required is too high for clinical use. More comprehensive research on GTC effects in breast cancer treatment is therefore needed.

Opposing studies

• A phase 1 study in lung cancer patients found no observable effect of green tea consumption on the tumor.
• A study in patients with esophageal cancer found insufficient evidence that green tea consumption benefited the disease.
• Evidence that green tea consumption reduces pancreatic cancer risk is insufficient.
• There is no evidence that green tea slows tumor progression in humans.
• Using green tea together with Bortezomib (brand name Velcade), used to treat multiple myeloma, reduces the drug’s effectiveness.

Breast cancer patients taking Tamoxifen (available as Nolvadex, Tamoxen, Tamofen or Soltamox) or Raloxifene (brand name Evista) with green tea experience increased effects of these drugs. This demonstrates that green tea interacts with medication. We therefore do not recommend green tea consumption, especially for people receiving hormonal treatment for breast cancer.

It is also unsuitable for patients with stomach ulcers because it increases stomach acid. It may additionally cause stomach complaints, liver damage, rashes and insomnia due to its caffeine content.

Conclusion

There are supportive and opposing studies about green tea’s effects on cancer. However, they are insufficient to demonstrate positive or negative effects of green tea consumption on cancer. More comprehensive research is needed in this area. We therefore do not recommend consuming green tea for cancer treatment or prevention.