Green tea and cancer: myths and realities

Écrit par Maxime DURAND

Tea is the second most consumed beverage in the world, with global production reaching 7.3 million tonnes in 2025. It is such a familiar part of our daily lives, and so widely praised for its wellness benefits, that organisations such as the Foundation Against Cancer have published information on green tea as a dietary supplement for people with cancer. So why has green tea attracted so much interest in cancer research?

What exactly is cancer?

The human body can be compared to a house. Its organs are the different rooms, while cells are the building blocks that make them up.

Cancer begins when cells stop functioning normally. This may result from errors that occur spontaneously when cells divide, from environmental factors or, less commonly, from inherited genetic changes. Cells normally have safety systems that can repair these errors or destroy cells that are too badly damaged.

When these systems fail, some cells can begin dividing uncontrollably and form a mass known as a tumour. However, not all tumours are cancerous. A benign tumour remains confined to one area, while a malignant tumour can invade surrounding tissues. This is cancer. Some cancers, such as leukaemia, do not form solid tumours.

Just as an electrical appliance needs electricity, cells need oxygen and nutrients carried by the blood. As a tumour grows, this supply may no longer be sufficient and some of its cells may die.

How do cancer cells overcome this problem?

They can release signals that encourage new blood vessels to grow towards the tumour. This process is known as angiogenesis. Cancer cells can also alter their surroundings and manipulate healthy cells to support their growth.

Some cancer cells can eventually break away from the original tumour and travel to other organs, particularly through the bloodstream. When they settle elsewhere and form a new tumour, this is called metastasis.

What do we know about green tea and cancer?

Green tea is not the only food or drink to contain antioxidants. However, it contains large amounts of catechins, molecules that researchers can isolate, measure and test. The best known and most widely studied catechin is EGCG.

The word “antioxidant” has played a major part in green tea’s reputation. As our cells function, they produce highly reactive molecules known as reactive oxygen species, or ROS. When present in excess, these molecules can damage cells and their DNA. Antioxidants can neutralise some of them.

In laboratory studies, EGCG can slow the growth of cancer cells, trigger their death and limit the formation of blood vessels that supply a tumour. Its effects depend on the surrounding conditions. EGCG can neutralise some reactive molecules, but it can also undergo oxidation itself. During this process, it may produce reactive molecules capable of damaging cancer cells.

Interesting experimental findings

When applied directly to cancer cells, EGCG can slow their growth and trigger their death. It has also slowed the growth of certain tumours in mice.

A study published in 2010 helps illustrate the gap between these experiments and drinking tea. Around 20 micromoles of EGCG per litre were needed to reduce the number of lung cancer cells grown in the laboratory by half. After drinking two or three cups of green tea, the highest concentration measured in human blood is around 0.6 micromoles per litre. This is more than thirty times lower than the concentration used in the laboratory.

Do tea drinkers develop fewer cancers?

To answer this question, researchers follow large numbers of people and compare tea drinkers with other participants. A publication from 2025 brought together 43 studies and reported a cancer risk around 9% lower among green tea consumers and 28% lower among people who consumed EGCG. These figures may sound encouraging, but most of the studies compared people who already drank tea with those who drank little or none. Other differences, including diet, smoking and physical activity, may also have influenced their cancer risk. This makes it difficult to determine how much of the difference was actually due to tea.

A larger analysis published in 2021 examined 113 studies covering 26 types of cancer and found almost no consistent protective effect. Results in humans therefore remain too contradictory to conclude that green tea prevents cancer.

What is actually tested in patients?

The move into patient research raises a very practical question: what should participants actually be given? In one trial, men with prostate cancer drank six cups of tea every day before surgery. Molecules from the tea reached the prostate, but had no clear effect on the growth of tumour cells.

To control the dose more precisely, researchers then turned to capsules containing standardised extracts such as Polyphenon E. In a study involving 97 men at high risk of prostate cancer, cancer was diagnosed in 5 of the 49 men who received the extract, compared with 9 of the 48 who received a placebo. The difference may appear encouraging, but the study was too small to confirm a preventive effect.

The results are less convincing in advanced cancer. Among 42 men who received a concentrated green tea preparation, only one showed an improvement, and it lasted for just two months.

Current research is therefore focusing more on prostate cancers that progress slowly. Two trials are comparing catechin capsules with a placebo to determine whether they can delay the progression of the disease. Their results are not yet available.

At this stage, the product being tested has more in common with a potential drug than with a cup of tea. Higher concentrations also bring different risks. Green tea extracts can cause rare cases of liver injury and interact with certain medicines. Anyone undergoing cancer treatment should therefore discuss the use of extracts or supplements with their healthcare team.

References

Maxime DURAND
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