Green tea (Chinese tea)

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.

In 2020, a Cochrane review looked into green tea being used for the prevention of cancer. Overall there were 1,100,000 participants across all of the studies that were looked into. Overall, the evidence showed that the effects of having green tea to lower cancer risk were inconsistent. They did find a slight improvement in quality of life for people who took green tea.

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

We need more evidence from randomised controlled clinical trials. This can help us to know whether green tea has a role in preventing cancer. At the moment it is not possible to draw any firm conclusions because:

• only a small number of studies have been done

• there is a lack of randomised controlled clinical trials

• there are differences in lifestyle factors within studies (most studies have been done in East Asia)

• different amounts of tea have been taken within the studies

• there is possible interaction with other treatments or diet supplements used by people in the studies

There is very little research into whether green tea or green tea extract can help treat cancer.

In 2012 an American study looked at taking a green tea extract called polyphenon E. They gave it to 42 patients. They all had a type of leukaemia called chronic lymphocytic leukaemia (CLL). The people in the trial were not taking any other kind of treatment.

The researchers found that in a third of people the number of leukaemic cells lessened. Their lymph nodes also shrank. This was a small trial, but the results were promising. We need larger trials before we will know whether green tea or its extracts can help people with cancer.

In another review study in 2018 researchers looked at using green tea and turmeric in people with CLL. They found limited evidence and mixed results that it might work.

Research has shown a possible interaction between green tea and the drug bortezomib (Velcade). This early research suggested that green tea might stop Velcade from working well. But we need much more research to find out if green tea has the same effect on humans.

Speak to your doctor if you are taking Velcade and you want to drink green tea. You might have to avoid green tea or the extract EGCG. Some people take EGCG as a supplement in liquid or capsules.