GREEN TEA

China and Japan have used green tea  as a medicine for many years. The tea is made from the steamed, unfermented leaves of the Camellia sinensis plant. It is also called Chinese tea.

Manufacturers promote it as a dietary supplement. They claim that it helps control blood sugar, cholesterol, blood pressure and weight. People also drink it because they believe it might prevent certain types of cancer.

The substance in green tea that researchers think is most helpful is a catechin. It is called epigallocatechin-3-gallate (EGCG). It also contains caffeine and theanine.

Why people with cancer use it

There is no real evidence that green tea can help treat cancer.

There is some evidence from early studies to suggest that having green tea might reduce the risk of some cancers. But at the moment the evidence is not strong enough to know this for sure.

People with cancer also drink green tea because they believe it might:

• boost their immune system which might help them fight their cancer
• improve health, energy levels and well being
• get rid of toxins in the body
• give them some control over their cancer and its treatment
• treat their cancer if no other conventional treatment can

GREEN TEA AND PREVENTING CANCER

Some laboratory studies have shown that extracts from green tea can stop cancer cells from growing.

Green tea contains substances called polyphenols. A sub group of these polyphenols is called catechins. Scientists think catechins give green tea it’s antioxidant properties. The catechin in green tea is called epigallocatechin-3-gallate (EGCG). Researchers think that EGCG has an anti-tumour(anti-cancer) effect.

These lab results are encouraging. But we need evidence from human studies to prove them. The evidence at the moment from human studies is mixed.

Researchers published an overview of studies (a meta analysis) in 2014. It suggested that green tea could reduce the risk of developing mouth cancers.

Other studies have shown it may reduce the risk of developing:

• lung cancer
• bladder cancer
• cancer of the food pipe (oesophagus).

Breast cancer

In 2018 researchers did another review and meta analysis of several studies. It showed that green tea might help to prevent breast cancer. And that it might especially help to prevent breast cancer from coming back. But the studies in the review were small. The researchers said that we need more scientific studies looking at greater numbers of people.

Prostate cancer

The research looking at whether it prevents prostate cancer generally and in pre cancerous prostate cells is mixed with some showing it might and others not showing any evidence. But a review study in 2018 suggests that the substances in green tea in laboratory research and early clinical trials suggests it may be of benefit. They suggest we need more research. 

Bowel cancer

Researchers did a study in 2017 on 39 patients. It was on people at risk of colon and rectal cancer. They found that green tea did not reduce the amount of aberrant crypt foci (ACF). ACF are groups of abnormal tube-like glands in the lining of the colon and rectum. They are early changes in the colon and rectum and can lead to cancer.

Research

Nurulain Zaveri, PhD, of SRI International in Menlo Park, Calif., reported on the green tea extract known as EGCG (epigallocatechin-3-gallate). Though this extract is thought to have anticancer properties, it’s not easily absorbed by the body. One would have to drink seven or eight cups of green tea a day to get an effective dose of EGCG.

Zaveri’s team developed a form of EGCG that’s more easily absorbed. In the test tube, it inhibits a breast cancer growth factor.

Iman Hakim, MD, PhD, of the Arizona Cancer Center, led a study in which smokers drank four cups a day of green or black tea. Decaffeinated green tea — but not black tea — cut down on one kind of DNA damage seen in smokers.

Jia-Sheng Wang, MD, PhD, of Texas Tech University, led studies of the effects of a green tea extract on people at high risk of liver cancer. Study participants received green tea polyphenols for three months. At the end of the study, they had lower levels of a chemical marker for liver cancer risk.@cancerqueries