Tea is the nation’s favourite drink and for good reason: it not only tastes great, but it’s good for our wellbeing as it is full of healthy ingredients
The health-enhancing flavonoids obtained from just two cups of tea a day reduces the risk of death from all-cause mortality by 40%, according to research published in the American Journal of Nutrition.[1]
Studies have found that drinking tea is associated with a reduced risk of heart disease, dementia, diabetes, high blood pressure and inflammation — which is recognised as a factor in many age-related health issues. Research shows it may even aid weight control and influence fat distribution.[2],[3],[4],[5]
Now an exciting new report, compiled by the Tea Advisory Panel, WHO BREW KNEW THAT? For Good Health, It’s Always Tea Time, explores the science and latest studies around the health benefits of tea. The report reveals in detail many of the ingredients – and their biochemical properties – that have been found to bring significant health benefits.
Dietitian and a member of the Tea Advisory Panel (TAP), Dr Carrie Ruxton says: “Tea is the ultimate superfood as it provides around 80% of the flavonoids in the UK diet and 70% of our dietary fluoride unlike other expensive superfoods with questionable claims and supposedly packed with antioxidant flavonoids.”[6]
Laboratory studies show that just one cup of tea delivers the same flavonoid activity as two apples, 3.5 glasses of orange juice or ten glasses of long-life apple juice.[7] Another, which focused on the oxidative stress which has a role in making arteries harden, found the flavonoids in tea were more potent antioxidants than vitamin C, vitamin E and beta carotene.
Professor Philip Calder, Professor of Nutritional Immunology within Medicine at the University of Southampton and a guest advisor to TAP, says: “Tea and other tea herbal infusions are such familiar friends, we often overlook the number, and range, of health benefits they bring to the table.
“Two of the biggest drivers for illness and age-related physical and cognitive decline are oxidation and inflammation, and tea helps combat both. It’s no wonder that drinking tea on a regular basis reduces the risk of so many health issues and barely a month goes by without fresh evidence of the benefits of a brew.”
What’s in a cuppa?
Black tea, which is the one we drink most often in the UK, and green tea more common in Asian countries are both produced from the same plant – Camellia sinensis – as is Oolong tea. Their distinctive flavours and flavonoid profiles stem from the fact that they are processed differently, and this may explain the different health benefits of different teas.
Scientists estimate that tea has around 4,000 bioactive compounds[8], with a third coming in the form of polyphenols, a family of natural plant composites which protect plants from ultraviolet radiation, bacteria, viruses and other damaging microorganisms. Polyphenols account for between 30% and 42% of the dry weight of tea and many have proven health-enhancing activity.[9],[10],[11]
Depending on their chemical structure, the polyphenols in tea fall into two main groups:
- flavanols such as EGCG (epigallocatechin gallate or epigallocatechin-3-gallate), EGC, (epigallocatechin) and ECG (Epicatechin gallate) and other catechins;
- flavonols such as quercetin, kaempferol.[12]
Tea scientist, Dr Tim Bond and a member of TAP says: “Plants have developed these polyphenols to protect themselves from a variety of threats, and there is clear evidence that many of these plant chemicals have potent bioactive properties which help protect human health, too.
“We know that many of the polyphenols found in tea are incredibly effective at removing excess reactive oxygen species [ROS], chemical messengers which are involved in DNA damage, inflammation, and many age-related diseases, when levels are too high.”[13]
Laboratory tests have found the flavonoids in both black and green tea have far higher antioxidant activity against peroxyl radicals — which promote inflammatory and neurodegenerative diseases — than are found in vegetables such as garlic, kale, spinach and Brussels sprouts, which are considered anti-carcinogenic.[14]
Dr Chris Etheridge from TAP, and a leading Medical Herbalist, says: “A number of flavanols and other plant chemicals present in tea have proven health properties, but there is also evidence that synergistic interactions between these compounds are responsible for some of the health benefits of tea. And as different teas are associated with different polyphenols and health benefits, it makes sense to break out of your routine and try a new brew.”
Tea catechins
The most abundant and biologically active catechin in tea is EGCG, which is known as epigallocatechin gallate or epigallocatechin-3-gallate. Laboratory tests have found that EGCG is not only more effective at killing cancer cells than 5-fluorouracil, a widely used chemotherapy drug, it also inhibits the growth of cancer cells.
EGCG and the catechins EGC (epigallocatechin) and ECG (Epicatechin gallate) — which have found anti-cancer activity (laboratory tests) — look and behave like molecules known as chaperones, which may help protect against cancer and have been tipped as the future of cancer therapy.[15],[16],[17],[18],[19],[20] They have also been shown to be potential DNA intercalators which could be another mechanism of action.[21]
But the benefits of these catechins extend far beyond cancer prevention. A recent review confirmed that EGCG, inhibits hardening of the arteries, thickening of heart muscle and damps down inflammatory markers and other factors which increase the risk of heart attacks and diabetes.[22] There is also evidence it can head off the vascular damage associated with diabetes and dementia.[23]
Quercetin a flavanol found in tea has a potent antioxidant and anti-inflammatory action and helps regulate immune response and reduce allergic reactions. Like the catechins in tea, quercetin protects against hardening of the arteries and exhibits anti-cancer activity.[24][25],[26],[27] It’s thought that quercetin and catechins could have a synergistic effect when combined, as they are in tea.[28],[29]
Kaempferol is another constituent of tea with proven anti-cancer activity. This stems from signalling pathways associated with inflammation, which often paves the way for cancer; programmed cell death, or apoptosis, which gives rise to cancer when it goes wrong; angiogenesis, which allows cancers to grow, and metastasis which allows them to spread around the body. [30] Kaempferol has also been shown to prevent and reverse ventricular fibrosis and cardiac dysfunction, providing an experimental basis for clinical treatment on ventricular fibrosis.[31]
Caffeine acts on a number of messenger chemicals in the brain to improve memory, alertness and mood and combat fatigue. A number of studies have shown it can improve physical performance.[32] But too much caffeine — more than 400mg in one serving — is associated with insomnia, irritability, nervousness and headaches.[33] Tea has half the caffeine of coffee – less than 50mg per mug – and more importantly, it has other active ingredients such as L-theanine which blunt the stimulation of caffeine and introduce feelings of calm concentration.[34]
Fluoride – tea is also one of the best sources of fluoride, necessary for strong teeth. A mug of black tea contains around 1.2mg of fluoride, so four servings achieve the recommended intake of 3.5mg (35).
L-theanine is an amino acid which is found almost uniquely in tea. It is a relaxant which blocks the vasoconstriction, or narrowing of the blood vessels, associated with caffeine. This may explain why drinking a lot of tea won’t produce the same jitters, headaches, raised blood pressure and heart palpitations associated with heavy coffee drinking.
Dr Etheridge from TAP says: “We have clear evidence of the bioactivity, modes of action and health benefits of many of the plant chemicals found in both black and green tea, but we are probably just scratching the surface when it comes to identifying and understanding all their health-enhancing properties.”
Dr Tim Bond from TAP adds: “We all instinctively know that tea is good for us, simply because it gives us such a lift. But as scientists continue to explore the different actions and interactions of its chemical components, we are beginning to unravel the secrets behind its proven health and benefits.”
References
[1] Kerry L Ivey, Jonathan M Hodgson, Kevin D Croft, Joshua R Lewis, and Richard L Prince. Flavonoid intake and all-cause mortality. Am J Clin Nutr 2015; 101:1012–20.
https://academic.oup.com/ajcn/article/101/5/1012/4577553
[2] https://www.cambridge.org/core/services/aop-cambridge-core/content/view/2D30740B08CD7CD2313BC180B139B9B9/S0007114515002329a.pdf/tea_consumption_and_mortality_of_all_cancers_cvd_and_all_causes_a_metaanalysis_of_eighteen_prospective_cohort_studies.pdf
[3] https://www.ncbi.nlm.nih.gov/pubmed/27925140\
[4] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3689013/
[5] https://www.ncbi.nlm.nih.gov/pubmed/25074392
[6] Lakenbrink C et al. (2000) Flavonoids and other polyphenols in consumer brews of tea and other caffeinated beverages. J Agric Food Chem, 48; 2848-2852
https://pubs.acs.org/doi/abs/10.1021/jf9908042;, Department of Health (1991) Dietary reference values for food energy and nutrients for the United Kingdom. Committee on Medical Aspects of Food Policy Report on Health and Social Subjects 41; Chan L et al. (2013) Human exposure assessment of fluoride from tea (Camellia sinensis L.): A UK based issue? Food Research International 51(2):564-70.
https://pubs.acs.org/doi/abs/10.1021/jf9908042
[7] Papanga G, et al (1999) The polyphenolic content of fruit and vegetables and their antioxidant activities. What does a serving constitute? Free Rad Res 30(2): 153-162
http://www.tandfonline.com/doi/abs/10.1080/10715769900300161
[8] //www.tuscany-diet.net/2014/04/26/tea-polyphenols-bioactive-compounds-leaves-tea-plant; Mahmood T, Akhtar N, Khan BA. The morphology, characteristics, and medicinal properties of Camellia sinensis’ tea. J Med Plants Res 2010; 4(19): 2028-33.
[9] Mahmood T, et al; The morphology, characteristics, and medicinal properties of Camellia sinensis’ tea.
http://academicjournals.org/journal/JMPR/article-full-text-pdf/A9725D815888
[10] Bhooshan Pandey, Imbrahim Rizvi (2009) Plant polyphenols as dietary antioxidants in human health and disease. Oxid Med Cell Longev
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2835915/
[11] Khan N, Mukhtar H; (2007) Tea polyphenols for health promotion. Life Sci 2007 Jul 26; 81(7): 519–533.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3220617/
[12] Mahmood T, et al; The morphology, characteristics, and medicinal properties of Camellia sinensis’ tea.
[13] Yang Y, et al. (2013) Reactive oxygen species in the immune system. Int Rev Immunol
https://www.ncbi.nlm.nih.gov/pubmed/23617726
[14] McKay DL, and Blumberg JB (2002) The Role of Tea in Human Health: An Update JACN 21:1-13
http://nutradvance.pt/wp-content/uploads/2016/04/Ref29.1.full_.pdf
[15] https://www.ncbi.nlm.nih.gov/pubmed/9095331
[16] https://www.ncbi.nlm.nih.gov/pubmed/23201840
[17] https://www.ncbi.nlm.nih.gov/pubmed/18068893
[18] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3490745/
[19] https://www.ncbi.nlm.nih.gov/pubmed/29024813
[20] https://www.ncbi.nlm.nih.gov/pubmed/28942499
[21] https://www.ncbi.nlm.nih.gov/pubmed/29059014
[22] https://www.sciencedirect.com/science/article/pii/S0378874117309893?via%3Dihub
[23] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5561811/
[24] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4808895/
[25] https://www.webmd.com/vitamins-supplements/ingredientmono-294-quercetin.aspx?activeingredientid=294&
[26] https://www.ncbi.nlm.nih.gov/pubmed/28942499
[27] https://www.ncbi.nlm.nih.gov/pubmed/29237430
[28] https://www.ncbi.nlm.nih.gov/pubmed/24573487
[29] https://www.ncbi.nlm.nih.gov/pubmed/11063442
[30] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3601579/
[31] https://www.ncbi.nlm.nih.gov/pubmed/29073623
[32] http://onlinelibrary.wiley.com/doi/10.1111/j.1467-3010.2007.00665.x/full
[33] https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/caffeine/art-20045678
[34] Dodd FL, et al (2015) A double-blind, placebo-controlled study evaluating the effects of caffeine and L-theanine both alone and in combination on cerebral blood flow, cognition and mood
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4480845/
[35] Ruxton C. H. S & Bond, T. J., Nutr. Bull, 2015, 40, 4, 268-278
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