“Do you want a coffee, Dave?”… “No thanks mate, I’m having my green tea”. Honestly, I used to think green tea was all hype. Something that the health freaks obsessed about. I would often hear muttered from their green tinted lips that it “helps fat loss” and “stops me from getting cancer”. Again, this added to my bullshitometer. Are they right? Does it really give you all of these cool benefits that green tea lovers harp on about? Or is it as much use to us as a chocolate teapot? What does the research say…?
Go get yourself a tea… this is a long one. Wait, maybe a green tea??? Hmmm…
What is Green tea?
Tea, in general, is made from leaf and bud of the plant Camellia sinesis and is widely drunk by millions of people around the world each day. Originating from China, tea is classified in to three main types: ‘non-fermented’ green tea; ‘semi-fermented’ oolong tea and ‘fermented’ black and red tea (basically, it’s been oxidized for longer). Approximately 76-78% of the tea produced and consumed by the public is black tea, 20-22% is green tea and <2% is oolong tea (1). Green tea is mainly produced from the plant Camellia sinesis var. sinensis and production is characterized by an initial heating process, which kills an enzyme known as polyphenol oxidase – which is responsible for the conversion of flavanols in the leaf into the dark polyphenolic compounds that give black tea it’s colour (2). The leaves are then cut and twisted.
The chemical composition of green tea is fairly complex (so bare with me here). Firstly, green tea is made up of proteins (15-20% dry weight) with amino-acids such as teanine (otherwise known as 5-N-ethylglutamine) and enzymes such as glutamic acid, tryptophan, glycine, serine, aspartic acid, tyrosine, valine, leucine, threonine, arginine and lysine. Not forgetting the carbohydrates cellulose, pectins, glucose, fructose and sucrose; lipids such as linoleic and linolenic acids; vitamins (B, C, E); xanthic bases such as caffeine and theophylline; various pigments such as chlorophyll and carotenoids; and minerals and trace elements such as Ca, Mg, Cr, Mn, Fe, Cu, Zn, Mo, Se, Na, P, Co, Sr, Ni, K, F, and A1 (3). Although these trace elements are dependent on what origin the green tea was manufactured (3). The most important component (for our article) of green tea are polyphenols, in particular the flavonoids. Flavonoids are phenol derivatives synthesized in substantial amounts and of various variety (4). The main flavonoids in green tea are catechins – epigallocatechin-3-gallate (EGCG, which is approx. 59% of the catechins in green tea), epigallocatechin (EGC, 19%), epicatechin-3-gallate (ECG, 13.6%) and epicatechin (EC, 6.4%) (5). It is believed that these catechins are the primary cause of any benefit that green tea may have on humans, although, there can be a large variation of catechin in different types of tea and these are not taken in to consideration with many studies (6). Oh and by the way, the use of milk or storing green tea in canned/bottled drinks does not affect the bioavailability of tea polyphenols (7).
So how does green tea affect humans?
Green tea affects us in three main ways; via caffeine, essential oils and the aforementioned polyphenolic compounds. Caffeine acts mainly upon the central nervous system, stimulating alertness, facilitating ideas association and decreases the sensation of fatigue (8). Green tea also contains theophylline, which has a vasodilator and diuretic effect. It also causes a non-specific relaxation on the bronchial smooth muscle, increasing respiratory stimulation (9). The essential oils help with digestion, although it has been found that extended brewing times can evaporate these essential oils (1). According to Santana-Rios and colleagues (2001), there isn’t much difference between a 3 and 5-minute brewing time for EGCG catechin content (10), so as long as you brew between those times, you’re getting a good amount of catechins.
The effects that catechins and polythenols have on human health are quite surprising. It has been found to have a higher antioxidant activity than vegetables such as garlic, kale, spinach and brussel sprouts (9) with promising evidence that these antioxidants can provide antidiabetic, antibacterial, anti-inflammatory properties and also provide protection against dental cavities and tooth loss (11). In human studies, researchers have observed that DNA damage, lipid peroxidation and free radical generation were reduced after participants drank 6 cups of green tea per day for seven days when compared to the control group (12).
Can green tea help prevent cancer?
This is the big one. This is what I’ve heard a lot about. Cancer kills millions each year, and if there is any way we can help prevent it, then it’s got to be worth a shot. But would I be wasting my time with green tea? Well, thankfully, no. Green tea consumption and protection against cancer has been supported by a myriad of evidence in animal and cell culture studies (13). Animal studies have shown that green tea inhibits carcinogenesis of the skin, lung, oral cavity, esophagus, stomach, liver, kidney, prostate, and other organs (14). In fact, green tea has been accepted by the National Cancer Institute as a cancer-chemopreventive agent (15).
However it is worth noting that these chemo-preventative properties may be dependent on its antioxidant action and the specific induction of detoxifying enzymes (9). A theory of green tea’s anti-cancer properties may be down to its effectiveness at helping decrease inflammation (with anti-inflammatory agents being used in current chemo-preventative strategies) with the EGCG catechin having large potential as an antioxidant, antimutagenic and chemo-preventive agent (16). In 2003, Wu et al. investigated green tea and breast cancer and found that women who drank green tea frequently demonstrated a decrease in breast cancer when compared to less frequent drinkers of green tea (less than once a month) (17). There have also been significant trends found on a decrease in breast cancer the more an individual increases their green tea intake (9). Similar results have been observed when investigating green tea with ovarian (18), prostate (9) and stomach cancer (19). But don’t go shouting from the hills just yet. Several other researchers have found no protective effect with green tea on stomach cancer (20, 21), therefor further studies are required with more detailed information to assess the role GT and gastric cancers. Similarly, the effects of GT on other cancers have been highlighted with inconsistent results (9, 22). In the majority of studies, the assessment of the use of green tea was based on a single question. This may lead to significant measurement errors. Besides, there are many other factors involved. For instance, those who regularly drink green tea, probably lead a more healthier, active life. These positive components may also help with the decrease in certain cancers. So it is very hard to simply pin-point the exact cause of any protective effects on cancers.
Green tea’s effects on cardiovascular disease
Many people are aware that the leading cause of death in both men and women is cardiovascular disease (23), so it’s probably a good idea to see if green tea has any positive effect on cardiovascular disease (CVD). Despite a few conflictions, several studies have suggested that green tea consumption is associated with a reduced CVD risk, however the mechanisms are currently uncertain (9). It has been hypothesized that green tea helps with LDL-cholesterol oxidation via EGCG antioxidant activity (the big catechin explained earlier). Seeing as LDL-cholesterol is a prime cause of cardiovascular complications (24), this is certainly a positive for GT. GT is also believed to help lipid metabolism and decrease cholesterol in the digestive tract, which then decreases overall cholesterol absorption (9). It has also been highlighted that men and women who consume 1-2 cups of green tea a day had a 44% lower risk of heart complications than those who didn’t drink tea (25). However, as highlighted with the cancer investigation, lifestyle factors make play a larger part in these healthy improvements.
GT has been associated with improvements in oral health, in particular a reduction in dental cavities and tooth loss (11). Not only is green tea a natural source of fluoride (it has even been added to toothpaste) (9), it has also been reported that GT can help reduce the periodontal breakdown in teeth from starchy foods (26). It has also been suggested that GT is photoprotective in nature, possibly reducing UVB and light-inducted skin disorders such as melanoma and non-melanoma skin cancers (26). There have also been positive outcomes when investigating GT and fat loss (9). From reducing long-chain triglycerides by 37%, to promoting fat oxidation and increasing thermogenic properties, GT may be a suitable accompaniment to a workout programme (9). It has also been found to help control insulin, glucose, triglycerides and free fatty acids in rats (27).
“There are many other factors involved. For instance, those who regularly drink green tea, probably lead a more healthier, active life. These positive components may also help with the decrease in certain cancers. So it is very hard to simply pin-point the exact cause of any protective effects on cancers”
GT has also been promoted as a good anti-bacterial and anti-viral supplement to asian diets and it has been found to inhibit the reproduction of certain bacteria, such as Salmonella, Clostridium and Bacillus (9). Even the good old Influenza virus, Adenovirus and the Herpes Simplex Virus has been found to get a bit of beef from green tea (28).
GT has even been shown to improve bone mineral density, strengthen the immune system (9) and even possibly prevent transplant rejection in humans (29). Recent studies even suggest that GT may possibly protect against the onset of Parkinson’s and Alzheimer’s disease (30), and of course, its anti-inflammatory properties can help with insect bites and stings (9).
Green tea has next to zero calories (if sugar is not added) and has a lower intake of caffeine than regular tea, coffee and cola drinks (9) with more vitamin C (31). It’s also easy to prepare, all you need is hot water and a variety of fruit and flavours can be added (such as cinnamon, mint and lemon). They’re also cheap to buy! I’ve just recently found 80 GT bags for £1.73. Bargain.
Now you’re thinking, ‘OK, so that was all the good stuff, here we go with the negatives”. Actually, if you’re a regular individual with no specific medical conditions – there aren’t any. The main concern is the caffeine intake, but with less caffeine than most other choices of hot drink, it’s actually not such a bad choice to make – especially with black tea having up to 67.4 mg/g of caffeine compared to 32.5 mg/g in GT (9). If you do suffer with heart complications then GT should be minimised (again, due to the caffeine intake) and it has been suggested that pregnant women should have no more than 1-2 cups/day (9). Those whom are also sensitive to aluminium (Al) should be very wary and consult their doctor before ingesting GT, as GT can increase the accumulation of Al. But like with anything new added to your diet, please consult your doctor before introducing new foods and supplements.
I initially wanted to slam green tea. I was fairly confident that evidence proved nothing and that actually, there are no real differences between green and black tea. Oh how I was wrong. Indeed, the claims that GT will decrease cancer are not set in stone. However, it has demonstrated that utilising green tea whilst promoting a healthy lifestyle may decrease the instances of some serious cancers. It’s prevention and treatment for many diseases is very promising and it’s antioxidant, antimutagenic, antidiabetic, anti-inflammatory, antibacterial and antiviral properties are extremely useful in maintaining and improving human health. Let’s not forget it’s oral health and solar protective capabilities. It also contributes to weight control, increases in bone density and stimulating the immune system. There is also evidence of GT helping to prevent neurodegenerative diseases. Of course, as previously explained, the possible positives may develop from participants with healthier lifestyles, especially with an association of GT and healthier individuals being a likely pair. But when we group all of the positives together, it’s clear to see that this inexpensive, widely available, easy to make hot drink has massive potential in inproving your health and wellbeing.
Right, whose turn was it to make the tea?
1 – Wu, C. D., & Wei, G. X. (2002). Tea as a functional food for oral health. Nutrition, 18, 443-444.
2 – Willson, K. C. (1999). Coffee, Cocoa and Tea. New York: CABI Publishing.
3 – Costa, L. M., Gouveia, S. T., & Nobrega, J. A. (2002). Comparison of heating extraction procedures for Al, Ca, Mg, and Mn in tea samples. Analytical sciences, 18, 313-318.
4 – Vinson, J. A., Dabbagh, Y. A., Serry, M. M., & Jang, J. (1995). Plant flavonoids, especially tea flavonols, are powerful antioxidants using an in vitro oxidation model for heart disease. Journal of Agricultural and Food Chemistry, 43, 2800-2802.
5 – McKay, D. L., & Blumberg, J. B. (2002). The role of tea in human health: an update. Journal of the American College of Nutrition, 21, 1-13.
6 – Henning, S. M., Fajardo-Lira, C., Lee, H. W., Youssefian, A. A., Go, V. L., & Heber, D. (2003). Catechin content of 18 teas and a green tea extract supplement correlates with the antioxidant capacity. Nutrition and cancer, 45, 226-235.
7 – Xu, J. Z., Yeung, S. Y. V., Chang, Q., Huang, Y., & Chen, Z. Y. (2004). Comparison of antioxidant activity and bioavailability of tea epicatechins with their epimers. British Journal of Nutrition, 91, 873-881.
8 – Varnam, A., & Sutherland, J. M. (1994). Beverages: technology, chemistry and microbiology (Vol. 2). Springer Science & Business Media.
9 – Cabrera, C., Artacho, R., & Giménez, R. (2006). Beneficial effects of green tea—a review. Journal of the American College of Nutrition, 25, 79-99.
10 – Santana-Rios, G., Orner, G. A., Amantana, A., Provost, C., Wu, S. Y., & Dashwood, R. H. (2001). Potent antimutagenic activity of white tea in comparison with green tea in the Salmonella assay. Mutation Research/Genetic Toxicology and Environmental Mutagenesis, 495, 61-74.
11 – Wu, C. D., & Wei, G. X. (2002). Tea as a functional food for oral health. Nutrition, 18, 443-444.
12 – Klaunig, J. E., Xu, Y., Han, C., Kamendulis, L. M., Chen, J., Heiser, C., & Mohler III, E. R. (1999). The effect of tea consumption on oxidative stress in smokers and nonsmokers. Proceedings of the Society for Experimental Biology and Medicine, 220, 249-254.
13 – Chung, F. L., Schwartz, J., Herzog, C. R., & Yang, Y. M. (2003). Tea and cancer prevention: studies in animals and humans. The Journal of nutrition, 133, 3268S-3274S.
14 – Laurie, S. A., Miller, V. A., Grant, S. C., Kris, M. G., & Ng, K. K. (2005). Phase I study of green tea extract in patients with advanced lung cancer. Cancer chemotherapy and pharmacology, 55, 33-38.
15 – Siddiqui, I. A., Afaq, F., Adhami, V. M., Ahmad, N., & Mukhtar, H. (2004). Antioxidants of the beverage tea in promotion of human health. Antioxidants and Redox Signaling, 6, 571-582.
16 – Hoshiyama, Y., Kawaguchi, T., Miura, Y., Mizoue, T., Tokui, N., Yatsuya, H., … & Hayakawa, N. (2004). A nested case–control study of stomach cancer in relation to green tea consumption in Japan. British journal of cancer, 90, 135-138.
17 – Wu, A. H., Yu, M. C., Tseng, C. C., Hankin, J., & Pike, M. C. (2003). Green tea and risk of breast cancer in Asian Americans. International journal of cancer, 106, 574-579.
18 – Zhang, M., Binns, C. W., & Lee, A. H. (2002). Tea consumption and ovarian cancer risk a case-control study in China. Cancer Epidemiology Biomarkers & Prevention, 11, 713-718.
19 – Asfar, S., Abdeen, S., Dashti, H., Khoursheed, M., Al-Sayer, H., Mathew, T., & Al-Bader, A. (2003). Effect of green tea in the prevention and reversal of fasting-induced intestinal mucosal damage. Nutrition, 19, 536-540.
20 – Borrelli, F., Capasso, R., Russo, A., & Ernst, E. (2004). Green tea and gastrointestinal cancer risk. Alimentary pharmacology & therapeutics, 19, 497-510.
21 – Koizumi, Y., Tsubono, Y., Nakaya, N., Nishino, Y., Shibuya, D., Matsuoka, H., & Tsuji, I. (2003). No Association between Green Tea and the Risk of Gastric Cancer Pooled Analysis of Two Prospective Studies in Japan. Cancer Epidemiology Biomarkers & Prevention, 12, 472-473.
22 – Nagano, J., Kono, S., Preston, D. L., & Mabuchi, K. (2001). A prospective study of green tea consumption and cancer incidence, Hiroshima and Nagasaki (Japan). Cancer Causes & Control, 12, 501-508.
23 – Centers for Disease Control and Prevention (accessed – 11/10/2016) – http://www.cdc.gov/heartdisease/facts.htm.
24 – Ishikawa, T., Suzukawa, M., Ito, T., Yoshida, H., Ayaori, M., Nishiwaki, M., … & Nakamura, H. (1997). Effect of tea flavonoid supplementation on the susceptibility of low-density lipoprotein to oxidative modification. The American journal of clinical nutrition, 66, 261-266.
25 – Sesso, H. D., Gaziano, J. M., Buring, J. E., & Hennekens, C. H. (1999). Coffee and tea intake and the risk of myocardial infarction. American Journal of Epidemiology, 149, 162-167.
26 – McKay, D. L., & Blumberg, J. B. (2002). The role of tea in human health: an update. Journal of the American College of Nutrition, 21, 1-13.
27 – Wu, L. Y., Juan, C. C., Ho, L. T., Hsu, Y. P., & Hwang, L. S. (2004). Effect of green tea supplementation on insulin sensitivity in Sprague-Dawley rats. Journal of Agricultural and Food Chemistry, 52, 643-648.
28 – Toda, M., Okubo, S., Ohnishi, R., & Shimamura, T. (1989). [Antibacterial and bactericidal activities of Japanese green tea]. Nihon saikingaku zasshi. Japanese journal of bacteriology, 44, 669-672.
29 – Bayer, J., Gomer, A., Demir, Y., Amano, H., Kish, D. D., Fairchild, R., & Heeger, P. S. (2004). Effects of green tea polyphenols on murine transplant-reactive T cell immunity. Clinical Immunology, 110, 100-108.
30 – Weinreb, O., Mandel, S., Amit, T., & Youdim, M. B. (2004). Neurological mechanisms of green tea polyphenols in Alzheimer’s and Parkinson’s diseases. The Journal of nutritional biochemistry, 15, 506-516.
31 – Hasegawa, N., Niimi, N., & Odani, F. (2002). Vitamin C is one of the lipolytic substances in green tea. Phytotherapy Research, 16, 91-92.
Share this article