Can Green Tea Prevent Cancer?
Green tea has always been a popular beverage. Loaded with antioxidants, it is touted to be anti-aging and helpful in losing weight. Besides many health benefits to its credit, one of the most controversial questions that seems to stand out is: Can green tea prevent cancer? With several claims put forward, this beverage is believed to contain compounds or chemicals that could win the war against cancer.
Originating from China (from where it was introduced to other parts of the world), green tea is made from the processed leaves of the Camellia sinensis plant. It became an item of interest to researchers when they observed that regions with high rates of green tea consumption had fewer cases of cancer.
Why green tea?
So, what is it that makes it super healthy? All forms of tea including green tea come from the dried leaves of the Camellia sinensis plant. The difference between black and green tie lies in the way the leaves are processed. The leaves of green tea are not oxidized, unlike those of black tea. making them provide a high level of antioxidants (about 30% of the dry weight of leaves).
People living in parts of East Asia and North Africa traditionally consume this beverage. Compounds contained in green tea include polyphenols such as flavandiols, flavanols, flavonols and phenolic acids. A large number of these mentioned polyphenols are known as catechins which have antioxidant properties and can also fight a range of diseases. The four types of catechins which are found in green tea include epigallocatechin, epicatechin, epicatechin-3-gallate and EGCG (1).
There are different types of green tea across the world, with sencha being the most popular and most easy to find. Other types of green tea which are well-known include:
- Fukamushi Ryokucha
- Gyokuro
- Kabusecha
- Matcha
- Tencha
- Genmaicha
- Hojicha
- Shincha
In recent times, matcha has been the favourite of most coffee shops and health food consumers. It is also considered to be the most premium variety of tea in Japan. However, it is interesting to note that there is more to this type of green tea.
What is the matcha green tea?
Matcha tea is a finely ground tea that has a bright emerald green color. An essential part of Japanese tea rituals for many centuries, this rich green tea has been popular in recent times because of its high concentration of antioxidants. When you consume matcha, you are drinking tea leaves which have been ground, providing you with more nutrients than the regular green tea.
Matcha is made from tea plants that are shaded for 14 days to boost the chlorophyll levels before harvest. It is usually available in powder form, but recently matcha in capsule form has been sold in stores.
Can Green Tea Prevent Cancer?
The antioxidant properties of catechins give green tea the ability to fight cancer. Antioxidants protect our cells from oxidative damage caused by unstable molecules known as free radicals (1). These molecules are naturally produced by the body during energy metabolism and immune reactions but various external factors, such as UV rays, unhealthy diet, smoking and stress, also contribute to the overwhelming production of free radicals. This causes oxidative damage to cells and can be harmful to our bodies in various ways, including causing gene mutations that result in the growth of cancer. Lately, there has been a massive interest in nutrients that can counter the activities of free radicals before they cause havoc in the human body.
Since there are more than 100 types of cancer, this article will only discuss the prevention of the most critical types of the disease namely breast, prostate, lung and colorectal cancer using green tea (2).
In addition, it is believed that it might have a boosting effect on the immune system, helps to eliminate toxins from the body and improves overall health and energy levels. All these properties make green tea a potential candidate as a natural agent to prevent or manage cancer.
1. Breast Cancer
Breast cancer is considered the most common cancer in women, and its association with green tea has been the subject of significant studies. Although some studies have not found a definitive link between green tea consumption and the prevention of breast cancer, there is ample evidence that suggests a strong association between the beverage and the disease. Compounds contained in the tea are discovered to have a possible effect on the mammographic densities (a significant risk factor for breast cancer) in younger women.
A randomized control trial conducted in 2017 observed the mammographic densities in women given a supplement of EGCG (the most popular catechin in green tea) for a year. While there was no change in the breast densities of older women, younger women experienced a significant decrease in this essential factor of breast disease (3).
Observing that the effect of the supplements was similar to the effects of tamoxifen, a medication used in breast cancer prevention, it was concluded that further research should be made to determine the role of green tea in reducing the risk of breast cancer in young women (4).
2. Prostate Cancer
This type of cancer is considered the second most frequently diagnosed cancer. In recent times many kinds of food including green tea has been suggested as a means to prevent the risk of cancer (including prostate cancer) in humans. Many recent studies investigating the possible effects of this beverage on this type of cancer show the benefits of green tea in inhibiting the growth of cancer, although the results do vary.
A systematic review and meta-analysis published in 2017 showed that adult males with high-grade prostatic intraepithelial neoplasia (HGPIN) had a lower risk of developing prostate cancer after consuming green tea catechins. This discovery suggests that the EGCG contained in these chemical compounds induced cell death and promoted cell growth arrest, thereby likely reducing the risk of this type of cancer in individuals that are most susceptible. Furthermore, that same study discovered that consuming as much as 7 cups a day may reduce the risk of prostate cancer. (5).
Additionally, a 2017 review article published by the University of Parma, reported the ability of green tea catechins to prevent prostate cancer is based on both the antioxidant properties of the green tea’s catechins, and its ability to target specific factors related to cancer development (6).
3. Colorectal Cancer
These types of cancers are considered one of the most common diseases that affect men and women alike. It is equally a significant cause of cancer-related deaths in the USA alone, and is expected to result in 50,630 fatalities in 2018 (7).
An optimistic discovery is that green tea has properties that can counter this deadly disease.
A meta-analysis published in 2017 revealed a protective association between colorectal cancers and green tea consumption. It showed a 7% reduction in risk in its consumers. It also showed that among young women, this risk is lowered up to 32% for every cup of green tea consumed. (8).
The same article went further to show that the EGCG in green tea inhibited the development of malignant colorectal cancer stem cells. This process happens when the polyphenol (EGCG) reduces the signal pathway (beta-catenin) which is essential for the development of such cells (8).
4. Lung Cancer
In 2012 an article by a Taiwanese university reported that the risk of lung cancer was higher in people who did not drink green tea. Additionally, it is 12 times higher in individuals who smoked (9).
A systemic review published in 2013 by the Canadian College of Naturopathic Medicine revealed that despite the presence of definitive evidence that links green tea with cancer prevention, further research was warranted to support the drink as a likely means of preventing lung cancer. (10).
In conclusion, the suggested activities of EGCG which might prevent the various forms of cancer, according to a 2018 article in the Egyptian Journal of Basic and Applied Sciences include (11):
- Promotion of cell death: EGCG targets specific cancer cells for ‘scheduled’ deaths. This death prevents the development of secondary tumors associated with cancer.
- Inhibiting of angiogenesis: This polyphenol restricts the growth of tumors by preventing the growth of new blood vessels needed to supply blood to the cancerous growth.
Regulation of cell growth: EGCG also modulates uncontrolled cell growth which is a significant feature of cancerous tumors. This process is done via cell cycle modulating proteins.
Side Effects and Precautions Related to Green Tea Consumption
Although matcha has a higher caffeine content than most other types of green tea, a cup of matcha contains lower levels of caffeine when compared to a cup of coffee.
With this in mind, although the matcha green tea is not an ideal option if you can’t handle caffeine in general, the effect of caffeine from green tea gives a feeling of being alert since it contains a high amount of the soothing amino acid L-theanine.
Consuming green tea on an empty stomach is not recommended since it may lead to stomach upset and nausea. Individuals with peptic ulcer or acid reflux are advised to drink it after a meal. Some evidence suggests green tea extracts should be discontinued if you have a liver problem and that it could interfere with some forms of medication (12).
Summing Up
- Green tea is derived from the tea plant and is consumed mostly in parts of Asia. The most potent form of green teas is the matcha which has a concentration of oxidants.
- This beverage is composed of chemicals that have properties that can offset the activities of free radicals which cause cancer.
- EGCG gives green tea most of its suggested chemo-preventive properties.
- As much as there is inconclusive evidence to support the ability of green tea to prevent cancer, many research studies have shown favourable results in some forms such as breast, lung, prostate and colorectal cancers.
- Green tea should be consumed moderately or avoided if you under certain medications.
