Highlights
Tea has strong antioxidant and anti-inflammatory properties and has multiple health benefits. Several laboratory studies also suggest possible benefits of taking different types of teas including green tea, black tea, ginger tea and hibiscus tea in cancer prevention. Many of these studies need to be conducted in human trials to confirm these benefits. While green tea was found to reduce breast cancer recurrence, a lab study also found that, epigallocatechin-3-gallate (EGCG), a key compound found in green tea, may reduce the efficacy of radiotherapy in prostate cancer cells. Hence, a personalized nutrition plan is needed to help with finding the right foods and supplements to complement the specific cancer treatment, rather than interfere with it.
Tea is one of the most commonly consumed beverages all over the world. It has various health benefits with different therapeutic and preventive properties. Hence, drinking a cup of tea daily is considered to be healthy. The different types of teas are broadly classified under 2 categories:
- Non-Herbal Tea
- Herbal Tea
Non-Herbal Tea
Non-herbal tea is made from the leaves of the Camellia sinensis plant. The three common types of non-herbal tea based on the processing or fermentation status of the tea leaves are :
- Green tea
- Black tea and
- Oolong Tea
The various processes of drying and fermentation determines the chemical composition of these tea types. All three forms of non-herbal tea contain antioxidants and caffeine in varying concentrations.
Green tea is produced from young fresh tea leaves and is not fermented. It is usually steamed or pan fried. Pan firing is done to avoid the fermentation of the tea leaves by the natural enzyme activities.
Black tea is made by allowing tea leaves to ferment for several hours before they are smoke fired, flame fired or steamed. It is made by oxidizing the tea leaves by exposing them to air. During oxidation, the leaves turn into a deep brown color and the flavor is intensified. These leaves are then left as such or are heated, dried and crushed.
Oolong tea is produced by just a partial oxidation of the leaves. It is produced predominantly in the Fujian province of China. Based on the scale of oxidation, it falls between Green tea and Black tea.
Herbal Tea
Herbal teas are generally made from herbs, berries/fruits, seeds, flowers, leaves or roots of different types of plants soaked in hot water. Based on the plant used for producing the tea, the chemical composition of herbal teas also vary. Herbal teas have lower concentrations of antioxidants than green, black, and oolong teas. They usually do not contain caffeine. Some examples of herbal tea are:
- Ginger Tea
- Chamomile Tea
- Hibiscus Tea
- Peppermint Tea
- Lemon Balm Tea
Nutritional Ingredients and Health Benefits
Let us now zoom into the active nutritional ingredients and health benefits of some of these herbal and non-herbal teas!
Green tea
A regular consumption of green tea is believed to help with numerous health problems.The different chemical constituents present in green tea include polyphenols, alkaloids, amino acids, proteins, volatile compounds, vitamins, minerals and trace elements.
Green tea contains a type of polyphenols called catechins. The major active constituents of green tea are catechins. A cup of green tea usually contains 30–42% catechins and 3–6% caffeine.
There are four types of catechins which include:
- Epigallocatechin-3-gallate (EGCG)
- Epigallocatechin (EGC)
- Epicatechin-3-gallate (ECG) and
- Epicatechin (EC)
Among the catechins listed above, Epigallocatechin-3-gallate, also known as EGCG, is one of the most abundant polyphenols present in green tea and is also found in oolong, and black teas. The anticancer properties of green tea may be attributed to EGCG. Most of the researches around the possible use of tea for cancer prevention are focused around this active ingredient. EGCG has strong antioxidant and antiinflammatory properties as well. Green tea also contains flavonols such as:
- Quercetin
- Kaempferol
- Myricitin
General Health benefits of Green Tea
Green tea is rich in antioxidants and has many health benefits. Listed below are some of the general health benefits of consuming Green tea:
- Helps in reducing the risk of Cardiovascular diseases
- Helps in boosting the brain function
- Helps in reducing risk of neurological disorders such as Alzheimer’s and Parkinson’s diseases
- Helps in weight loss
- Helps in reducing cavities and tooth decay
- Helps in burning fat and decreasing obesity.
- Helps in reducing the risk of diabetes
As green tea is rich in EGCG, many observational studies have been carried out to evaluate the effect of green tea consumption on cancer prevention. Some of the studies that investigated the role of green tea or its constituent EGCG in cancer or cancer prevention are summarized below.
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Benefits of Green Tea in Cancer Prevention/Treatment
Green tea consumption and Breast Cancer Recurrence/Incidence
A study done by the medical researchers from the University of Perugia in Italy based on data from 163,810 people found that an increased consumption of green tea significantly reduced the risk of breast cancer recurrence. However, its impact on reducing breast cancer incidence was inconclusive. (Gianfredi V et al, Nutrients., 2018)
In a similar study, the researchers from the Mashhad University of Medical Sciences in Iran analyzed data from 14 studies which included 9 case-controlled studies, 4 cohort studies and 1 clinical trial. They found that in the case-controlled studies, women who received the highest levels of green tea had a 19% reduction in breast cancer risk compared to those who received the lowest levels of green tea. However, the clinical trial data showed that green tea consumption didn’t alter the mammographic/breast density compared with control. Hence, the overall conclusion of this group on the possibility of green tea reducing breast cancer risk was inconclusive. (Najaf Najafi M et al, Phytother Res., 2018)
In another study done by researchers from China, the researchers analyzed data from 14,058 breast cancer patients and found that green tea consumption may decrease the risk of cancer incidence. However, the researchers suggested more properly designed trials to clarify the protective association between green tea consumption and breast cancer incidence (Yu S et al, Medicine (Baltimore), 2019).
In short, some observational studies indicate that green tea consumption may be associated with a decreased risk of breast cancer recurrence. However, more well-designed clinical studies are required to confirm the protective association between green tea intake and breast cancer incidence.
Green tea consumption and Prostate Cancer Risk
Researchers analyzed questionnaire-based data from the JPHC Study (Japan Public Health Center-based Prospective Study) which included 49,920 men aged 40–69 years and found that green tea consumption was not associated with localized prostate cancer. However, green tea consumption was associated with a dose-dependent decrease in the risk of advanced prostate cancer. (Kurahashi N et al, Am J Epidemiol., 2008)
In summary, the findings indicate that Green tea consumption may be associated with a decreased risk of advanced prostate cancer.
At the same time, a lab study has found that Green tea extract (epigallocatechin-3-gallate – EGCG) may reduce the efficacy of radiotherapy in prostate cancer cells. (Francis Thomas et al, Urology., 2011) Hence, you should consult with your oncologist before taking EGCG supplements while on treatment with radiotherapy for prostate cancer.
Green tea consumption and Colorectal Cancer Risk
In a recent study, the researchers conducted a dose-response meta-analysis on data from 29 literatures extracted from Pubmed and Embase databases with a total of 1,642,007 subjects and found that green tea consumption may have a protective effect among females and colorectal cancer patients.(Chen Y et al, Oncotarget., 2017)
In another study, the researchers conducted a meta-analysis of six prospective cohort studies involving 352,275 participants and found that increasing consumption of green tea by 1 cup/day had no impact on the incidence of colorectal cancer. (Wang ZH et al, Nutr Cancer., 2012)
The researchers concluded that available data from prospective cohort studies are insufficient to conclude that green tea may protect against colorectal cancer.
Green tea consumption and Ovarian Cancer Risk
A recent study using data from a comprehensive literature search until 14 May 2017 using electronic databases such as PubMed, EMBASE, Web of Science and Scopus found that Green tea intake may be associated with a reduced risk of ovarian cancer. (Zhang D et al, Carcinogenesis., 2018)
In short, unlike black tea, green tea consumption may reduce the risk of ovarian cancer. However, more well designed clinical studies are required to support the same.
Green tea consumption and Liver Cancer Risk
A recent meta-analysis used data from 10 studies including 6 cohort and 4 case-control studies based on literature search in PubMed, EMBASE, Cochrane database, and Chinese databases including Chinese Biomedicine Database and Chinese National Knowledge Infrastructure (CNKI) database up to April 29, 2015. The study found that those with highest intake of green tea ((≥5 cups/day) had a 38% reduced risk of liver cancer (preventive effect) as compared to non-drinkers. (Ni CX et al, Nutr Cancer., 2017)
EGCG supplementation for Radiation induced esophagitis/swallowing difficulties
In a phase II clinical study conducted by the Shandong Cancer Hospital and Institute in China, analysis of data from a total of 51 patients found that EGCG supplementation reduced esophagitis/swallowing difficulties in esophageal cancer patients without negatively impacting the efficacy of radiation therapy. (Xiaoling Li et al, Journal of Medicinal Food, 2019).
In summary, green tea consumption may have a protective association against few specific types of cancer, however more studies are required to confirm the same. Studies also confirm that it may help in reducing certain side effects of specific cancer treatments.
Black Tea
Black tea is the most abundantly used tea across the world. According to the statistics from the Tea Association of the United States, in 2019, about 84% of the tea consumed in the United States was black tea, 15% was green Tea, and only a small remaining amount was oolong tea. Black tea has a high caffeine content compared to other teas, and hence may be used as an alternative beverage for coffee.
The key active ingredients of black tea includes :
- Thearubigins
- Theaflavins
- Flavonols and
- Catechins
During the fermentation of fresh tea leaves, some of the catechins get oxidized to theaflavins including theaflavin, theaflavin-3-gallate, theaflavin-3′-gallate and theaflavin-3-3′-digallate and thearubigins. These provide a bitter taste to black tea. The dark color of black tea is also obtained from thearubigins and theaflavins.
Now, let us peep through the nutritional and health benefits of black tea.
General Health benefits of Black Tea
Like green tea, black tea also contains antioxidants and has similar health benefits. Mentioned below are some of the health benefits of black tea :
- Helps in reducing the risk of stroke
- Helps in reducing inflammation in the body
- Helps to improve cardiovascular/heart health
- Helps to improve gum and teeth health
- Helps in reducing blood pressure
- Helps in reducing diabetes/lowering blood sugar levels
Unlike green tea, a limited number of human intervention studies have been carried out on regular intake of black tea to demonstrate its anti-cancer benefits/chemopreventive potential. Some of these studies are summarized below.
Benefits of Black Tea Consumption in Cancer Prevention / Treatment
Black tea consumption and Breast Cancer Risk
A recent analysis used data from the Sister Study, a prospective cohort study supported by the National Institute of Environmental Health Sciences (NIEHS) that enrolled 45,744 women between the ages of 35 and 74 across the United States and Puerto Rico from 2003 to 2009. The study suggested that drinking around five cups of green or black tea per week may be associated with a decreased breast cancer risk. (Zhang D et al, Int J Cancer., 2019)
Due to inconsistencies in the outcomes of the analysis from different observational studies, more clinical studies are needed to confirm the protective association between black tea consumption and breast cancer risk.
Black tea consumption and Ovarian Cancer Risk
A recent study used data from a comprehensive literature search until 14 May 2017 using electronic databases such as PubMed, EMBASE, Web of Science and Scopus and found that black tea consumption did not have any significant benefit on ovarian cancer risk. (Zhang D et al, Carcinogenesis., 2018)
Black Tea consumption and Esophageal Cancer
In a recent analysis, researchers conducted a population-based case-control study in a high esophageal squamous cell carcinoma risk area in China and used a questionnaire-based data for analysis and found that drinking very hot tea with temperature >65°C was significantly associated with an increased risk of esophageal squamous cell carcinoma compared to non-drinkers. The study also found that irrespective of the frequency, intensity and tea leaf amount, black tea intake was significantly associated with a higher risk of esophageal cancer. (Lin S et al, Eur J Cancer Prev., 2020)
Black Tea consumption and Colorectal Cancer Risk
There are different studies and evidence from in vitro and animal models suggesting black tea as a potential chemopreventive agent against colorectal cancer. However, the results are inconsistent across 20 individual observational studies. Hence, the association between black tea consumption and colorectal cancer risk is inconclusive. (Can-Lan Sun et al, Carcinogenesis, 2006)
In summary, human studies done so far have not shown any substantial evidence to support the protective association/benefits of black tea intake on cancer prevention, even though in vitro and in vivo studies suggested possible anticancer effects/benefits of black tea. More studies are required to establish the benefits of taking black tea for cancer prevention.
Ginger Tea
Ginger is one of the most popular spices used in the Asian countries. Ginger tea is a herbal tea prepared by boiling the aromatic ginger root for at least 10 minutes in water. Ginger has many health benefits due to its anti-inflammatory, antibacterial, antiviral, and anti-cancer properties. The health benefits of ginger tea are mostly attributed to their polyphenols.
The key ginger tea polyphenols include:
- Gingerols
- Shogaols and
- Catechins
Gingerols are the major polyphenols in fresh ginger. Examples are: 6-gingerol, 8-gingerol & 10-gingerol.
Gingerols are converted into shogaols during long time storage or by heat treatment.
Shogaols are converted into paradols post hydrogenation.
Other phenolic compounds present in ginger are quercetin, zingerone, gingerenone-A, and 6-dehydrogingerdione.
Terpene components present in ginger include:
- β-bisabolene
- α-curcumene
- Zingiberene
- α-farnesene
- beta-sesquiphellandrene
Polysaccharides, lipids, organic acids, and raw fibers are also present in ginger.
General Health Benefits of Ginger Tea
Ginger tea is known to have many health benefits due to its strong antioxidant and anti-inflammatory properties. Some of the general health benefits associated with ginger tea include:
- Antioxidant activity
- Antiemetic effect – helps in reducing nausea and vomiting as well as motion sickness
- Anti-inflammatory activity – helps with pain and inflammation
- Gastroprotective effect – helps in reducing risks of gastric ulcers, Helps in relieving stomach pain, helps in reducing gas and bloating
- Anti-diabetic activity – May help in lowering sugar levels
- Helps in reducing osteoarthritis pain
- Helps in digestion
- Helps in boosting circulation
- Antimicrobial activity against gum bacteria
- Helps in treating colds or flu
Benefits of Ginger Tea in Cancer Prevention/Treatment
Ginger Tea Consumption and Chemo induced Nausea and Vomiting in Cancer Patients
In 2019, a systematic review was done which analyzed a total of 18 articles to evaluate any possible benefit of ginger on adults undergoing chemotherapy in relation to vomiting and nausea. Though the researchers couldn’t find the ideal dosage of ginger that should be given to patients due to clinical heterogeneity between all the trials conducted, they concluded that ginger supplementation in conjunction with standard antiemetic care may be beneficial for chemotherapy-induced vomiting and chemotherapy-induced nausea and vomiting related outcomes. (Crichton M et al, J Acad Nutr Diet. 2019 )
Ginger Tea Consumption and Cancer Prevention/Treatment
Many in vitro, in vivo and a few clinical studies suggest that taking ginger has the potential for the prevention and treatment of different gastrointestinal cancers including Gastric Cancer, Pancreatic Cancer, Liver Cancer, Colorectal Cancer and Cholangiocarcinoma. (Prasad S et al, Gastroenterol Res Pract., 2015)
In summary, taking Ginger tea seems to be beneficial due to its multiple health benefits. These health benefits may be attributed to polyphenols present in ginger tea. However, drinking excess ginger tea can upset the stomach and lead to loose stools. One should avoid drinking ginger tea if taking anticoagulant and antiplatelet medications, since it can slow down the clotting of blood. Ginger tea should also be avoided if we have heartburn and acid reflux.
Hibiscus tea
Hibiscus tea is another herbal tea made from the Hibiscus sabdariffa plant. It is usually made by soaking flowers and other parts of the hibiscus plant in boiling water. The key active ingredients of hibiscus extract/tea include :
- Anthocyanins like delphinidin-3-glucoside, sambubioside, and cyanidine-3- sambubioside
- Sterols such as β-sitoesterol and ergoesterol
- Flavonoids such as gossypetine, hibiscetin and their respective glycosides; protocatechuic acid, eugenol
Delphinidine-3-sambubioside is the major source of antioxidant property of hibiscus extract. The leaves of Hibiscus sabdariffa plant are a good source of various nutrients like protein, fat, carbohydrates phosphorus, iron, β-carotene, riboflavin and ascorbic acid. They contain high levels of polyphenolic compounds such as chlorogenic acid, quercetin and kaempferol glycosides that also contribute to the antioxidant capacity and anti-inflammatory activity.
General Health Benefits of Hibiscus Tea
Different studies have shown that hibiscus tea have multiple health benefits. Some of the benefits of consuming hibiscus tea are listed below:
- Helps in lowering blood pressure
- Helps in fighting bacteria
- Helps in weight loss
Some in vitro and in vivo studies suggest an antimicrobial effect of hibiscus tea, but lack human studies to establish this health benefit.
Benefits of Hibiscus Tea in Cancer Prevention/Treatment
Different in vitro and in vivo studies evaluated the possible benefits of hibiscus tea in Cancer and their results indicate that hibiscus extracts can inhibit the growth of cancer cells in cancers including breast cancer, leukemia, and melanoma/skin cancer. Recent studies also found that Hibiscus polyphenols may inhibit melanoma cell growth and viability. (Goldberg KH et al, J Tradit Complement Med. 2016)
However, even though these findings look promising, further well-designed human trials are required to establish any possible benefits of hibiscus tea in cancer prevention/treatment.
Conclusion
In summary, tea has multiple health benefits and drinking a cup of tea daily is considered to be healthy. Several in vitro and in vivo studies also suggest possible benefits of taking different types of teas including green tea, black tea, ginger tea and hibiscus tea for cancer prevention or reducing the side effects of cancer treatment. However, many of these findings and benefits, especially for black tea, ginger tea and hibiscus tea, are yet to be validated in human trials.
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