Black tea, green tea and oolong tea are made from the same plant, Camelllia sinensis, a small bush with yellow-green serrated leaves, originating from China. Green tea is prepared from leaves which are steamed and then rolled, while black tea and oolong tea are produced when the leaves are allowed to partially ferment.

Tea is the most often consumed beverage in the world and green tea in particular is drunk several times a day in countries such as China and Japan. In fact, the Ohsaki National Health Insurance Cohort Study was set up in order to investigate the supposed health benefits of regular green tea consumption in Japan, and with impressive results: with more than 40,000 people enrolled, the scientists found that over 11 years there was a significant inverse association between tea consumption (5 cups or more per day compared to one or less) and mortality from all causes. The inverse association was even stronger for mortality from cardiovascular disease, especially stroke.¹

Drinking tea stimulates gastric acid production which helps with an age-related decline in digestive function and therefore improves the absorption of nutrients. Green tea is also mildly antibacterial and antiviral, so its regular consumption helps maintain gastrointestinal health and prevent dysbiosis.² Tea is also a diuretic so it helps cleanse the kidneys and encourages the removal of problem fluids and wastes from the body in cases where there is a sluggish metabolism.

Tea stimulates heat production from brown fat, raising the metabolic rate in the process, and so helps a constitution prone to weight gain. Tea also reduces pancreatic lipase secretion, which is an enzyme necessary for fat digestion, and therefore fat absorption. Furthermore, tea reduces blood sugar levels, while simultaneously increasing insulin sensitivity, thereby assisting with other aspects of the so-called metabolic syndrome such as insulin resistance and diabetes which increasingly afflict modern civilisation.³

As a circulatory system herb, tea protects the heart and vessels by inhibiting platelet aggregation and lowering serum cholesterol and triglyceride levels. The polyphenols tea contains include catechins, epicatechin, proanthocynidins, and epigallocatechin are responsible for strong antioxidant and anti-inflammatory activity which is also protective of the heart and blood vessels.⁴ As a result, the overall effect of drinking green tea regularly is to reduce the risk of developing cardiovascular disease and promote longevity, as is seen in the traditional lifestyle of the Okinawan people who regularly drank green tea.

Tea contains the methylxanthines caffeine, theobromine and theophylline which make tea a stimulant to the nervous system, increasing alertness and memory. Tea also contains the amino acid theanine which can raise levels of the neurotransmitters dopamine and serotonin, thereby elevating mood as well as reducing stress.

Apart from the caffeine content and other stimulant compounds which make tea a good aid to study and memory, green tea is also broadly neuroprotective and is being researched for its benefits in preventing or treating dementia. In this respect, green tea demonstrates free-radical-scavenging activity by encouraging antioxidant enzymes, as well as chelating iron and copper which contribute to oxidative stress. Green tea catechins circulate in the body as well as travel across the blood-brain barrier, modulating gene expression and cell-signalling pathways, thereby demonstrating direct and indirect effects on the brain and nervous system. More specifically, as demonstrated in experimental animal models, green tea catechins offer protection to the brain after damage due to stroke, helping to keep cells alive and their mitochondria viable while reducing oedema which causes further damage. They also inhibit the formation of amyloid-β, an important molecule in Alzheimer’s disease progression, as well as help clear it away from brain tissue.⁵

Green tea is active against several types of cancer cells in the lung, skin, colon and prostate.⁶ In the case of prostate cancer, green tea phytonutrients have been found to lower the level of prostate specific antigen (PSA) and help to prevent progression from premalignant states to cancer.⁷ Green tea is also an inhibitor of the enzyme 5-a-r reductase and is therefore useful in treating benign prostatic hyperplasia (BPH).

As a fermented drink called kombucha, tea has the added advantage of being a probiotic drink. To make kombucha, sweetened tea is fermented using a ‘mushroom’ which comprises a symbiotic mix of yeast and acetic acid bacteria. You can also make chai with the addition of various tasty and aromatic spices.

References:

1.         Kuriyama S, Shimazu T, Ohmori K, et al. Green tea consumption and mortality due to cardiovascular disease, cancer, and all causes in Japan: the Ohsaki study. JAMA 2006;296:1255–65.

2.         Braun, Cohen. Herbs & Natural Supplements, An Evidence-based guide. Elsevier; 2005.

3.         Sae-tan S, Grove KA, Lambert JD. Weight control and prevention of metabolic syndrome by green tea. Pharmacol Res 2011;64:146–54.

4.         Grassi D, Desideri G, Di Giosia P, et al. Tea, flavonoids, and cardiovascular health: endothelial protection. Am J Clin Nutr 2013;98:1660S–1666S.

5.         Kidd PM. Bioavailability and activity of phytosome complexes from botanical polyphenols: the silymarin, curcumin, green tea, and grape seed extracts. Altern Med Rev J Clin Ther 2009;14:226–46.

6.         Khan N, Mukhtar H. Tea and health: studies in humans. Curr Pharm Des 2013;19:6141–7.

7.         Lambert JD. Does tea prevent cancer? Evidence from laboratory and human intervention studies. Am J Clin Nutr 2013;98:1667S–1675S.