Tea is one of the most popular drinks in the world, second only to water. Green tea, black tea, white tea, oolong tea and pu-erh tea are all made from the young leaves and leaf buds of the same shrub, Camellia sinensis. Two main varieties are used, the small-leaved China tea plant (C. sinensis sinensis) and the large-leaved Assam tea plant (C. sinensis assamica).
- Green tea versus black and other tea
- Tea antioxidants
- Caffeine in tea
- Matcha tea
- Tea health benefits
- Green tea and weight loss
- Tea and coronary heart disease
- Tea and diabetes
- Tea and asthma
- Tea and stress
- Tea and cancer
- Tea and osteoporosis
- Drinking tea could help you live longer
- Tea nutrition facts
- Green tea extracts
- How to enjoy tea
Green tea versus black and other tea
Green tea is made by steaming and drying fresh tea leaves immediately after harvesting. The lack of fermentation gives green tea its characteristic flavour and helps to preserve almost all of the naturally present polyphenols. Green tea is often described as having an astringent, grass-like taste.
White tea is similar to green tea, in that it is not fermented, but is only made from new, baby tea buds that are hand-picked before they open. These have a white appearance due to the presence of fine, silvery hairs. The buds are gently dried and make a tea that is pale, straw coloured and delicately fragrant – described as light and sweet.
Black tea is made from freshly cut tea leaves that are crushed and then fermented so they oxidize before drying. Natural enzymes in the tea leaves produce the characteristic red-brown colour and reduced astringency. Black tea represents 78% of the tea brewed worldwide, and is the most common variety brewed in the West.
Pu’er or pu-erh tea undergoes further microbial fermentation to produce a darker form of black tea and is produced in Yunnan province, China.
Oolong, or brown tea, fits somewhere between green and black tea, in that the leaves are only partially fermented.
Tea contains antioxidants similar to those that give red wine, dark chocolate and cocoa their health benefits. These tea antioxidants are at least 100 times more powerful than vitamin C, and 25 times more powerful than vitamin E.
Over 30 per cent of the dry weight of green tea leaves consists of powerful flavonoid antioxidants classed as catechins, such as epigallocatechin-3-gallate (EGCG). Matcha, a powdered green tea, contains at least three times more EGCG than normal green tea.
During fermentation to produce black tea, the catechins are converted into more complex antioxidants such as theaflavins and thearubigins. Black tea contains around 10% catechins by weight, plus 6% theaflavins and around 18% thearubigins, as well as other flavonoids such as quercetin.
Adding milk to black tea was originally through to bind the antioxidants and reduce their bioavailability. However, recent studies have found no difference in antioxidant status when volunteers drank tea with milk compared to when they drank it without milk.
Black tea, as brewed in the UK, provides around 200mg total flavonoids per cup. Drinking three cups per day (made using 2g dry tea leaves per cup) will increase the concentration of antioxidant flavonoids in your blood by 25%.
Drinking four to five cups of tea per day provides more than half of most people’s dietary intake of flavonoid antioxidants – other sources include fruit and vegetables especially apples and onions, as well as cocoa and dark chocolate.
Caffeine in tea
Tea is a natural source of caffeine. White tea contains around 15mg caffeine per cup, compared to 20mg for green tea and 40mg for black tea. In comparison, a cup of coffee supplies between 75mg and 100mg.
However, tea leaves also contain a unique amino acid called L-theanine which, when consumed together with caffeine, has an alerting effect without causing stress responses and ‘jitteriness’. The results from 11 clinical trials show that caffeine plus l-theanine improves alertness and attention with the strongest effects seen during the first hour post-dose. So, unlike getting your caffeine from coffee, the caffeine in tea is less likely to cause over-stimulation or to interfere with sleep.
Matcha tea contains particularly high amounts of L-theanine.
Matcha tea is made from green tea leaves that are ground down to form a fine green powder. This releases the antioxidants and, as you consume the whole, powdered leaf , you absorb up to 15 times more than when drinking an infusion of leaves.
Matcha tea powder is traditionally whisked into hot water using a bamboo whisk. Buddhist monks traditionally used matcha to stay alert and focused throughout meditation, while Samurai warriors used matcha tea as an energy fix before battle.
The best sources of organically grown matcha are said to come from the Uji region of Japan.
Tea health benefits
Green tea was once thought to have more health benefits than black tea, but this was purely because early research focussed on green tea. Now, it is accepted that black tea and green tea have similar health benefits.
Drinking tea is not only refreshing, but is associated with health perks such as significantly reducing your risk of developing high blood pressure, raised cholesterol, stroke, obesity, type 2 diabetes and depression. As a result, tea drinks have been found to live longer than non-tea drinkers.
Green tea and weight loss
Green tea extracts can boost the rate at which the body burns calories by as much as 40% over a 24 hour period. Green tea (and to a lesser extent black tea) helps to reduce weigh in several different ways, by:
- Suppressing appetite and reducing food intake through effects on hormones such as ghrelin and adiponectin
- Blocks the activity of intestinal enzymes (gastric and pancreatic lipases) needed to digest dietary fat, so that 30% less dietary fat is emulsified and absorbed.
- Inhibiting a metabolic enzyme (catechol-0-methyl transferase), green tea stimulates the amount of fat burned in cells to release energy so that you generate more heat – a phenomenon known as thermogenesis.
- Green tea was recently found to activate an enzyme (AMP-protein kinase) that has effects on the liver to decrease glucose and fatty acid synthesis and increase their break down for energy.
Several trials have found that adding green tea extracts to a weight loss regime helps to improve fat loss. For example, a study involving 60 obese adults following a prepared diet of 3 meals a day found that, compared with placebo, those taking green tea extracts lost an additional 2.7kg during the first month, 5.1 kg during the second month and 3.3kg during the third month. Another trial involving 80 overweight men and women found that adding green tea extracts to a slimming diet increased weight loss by 3.5kg over 3 months
One of the most recent studies involved 115 overweight women who took a green tea extract (EGCG) at a daily dose of 856.8 mg or placebo for 12 weeks. They were instructed to maintain their former diet, eating habits, and level of physical activity. Despite making no other changes, those taking the green tea extract lost an average of 1.1 kg in weight, a reduction in waist circumference of 2.3cm over 3 months.
Tea and coronary heart disease
Drinking black, green, white or related teas has beneficial effects on blood lipids, reducing the oxidation of LDL-cholesterol so less is deposited in artery walls. Tea also lowers blood pressure and blood stickiness, and increases the elasticity of blood vessel walls to improve blood flow. Tea antioxidants also slows the progression of coronary artery calcification.
The results from 22 studies following a total of 856,206 people, found that, overall, an increase in tea consumption of 3 cups per day was associated with a 27% reduced risk of coronary heart disease, a 26% lower risk of cardiac death an 18% lower risk of stroke, and a 24% lower risk of dying from any medical cause during the duration of the studies.
For example, when almost 200,000 men and 288,000 women aged 30-79 years were followed for 7 years, those who drank tea every day were 10% less likely to experience a heart attack during those 7 years than non-tea drinkers.
In a study involving 774 elderly men who were followed for 25 years, those with the highest intake of epicatechin antioxidants (half of which came from tea, and half from other sources such as apples and cocoa) were 38% less likely to die from coronary heart disease than those with the lowest intakes. Those with existing cardiovascular disease were also 46% less likely to die from a stroke.
Tea and diabetes
- blocking digestive enzymes (pancreatic alpha-amylase and intestinal alpha glucosidases) which break down starchy carbohydrates, so that less glucose is absorbed
- damping down the rise in blood glucose levels that normally occur after eating
- increasing insulin sensitivity.
These actions are similar to those of the prescribed anti-diabetes drug, acarabose, which is classed as an alpha-glucosidase inhibitor.
People with type 2 diabetes who drank 1500 ml oolong tea (around 5 mugs) every day for 30 days reduced their blood glucose levels by as much as 30% compared with a similar period when they drank water, for example.
The beneficial effects of drinking black tea are synergistic with those of acarbose, and researchers have suggested that black tea could help to prevent the onset of type 2 diabetes, or postpone the need for starting drug treatment.
The results from studies involving over 545,500 people now show a clear relationship between the number of cups of tea you drink per day, and the risk of developing type 2 diabetes. Compared with drinking no tea, the relative risk of developing type 2 diabetes is:
- 3% lower for one cup of tea per day
- 5% lower for drinking two cups of tea per day
- 7% lower for three cups of tea per day
- 10% lower for drinking four cups of tea per day
- 12% lower for five cups of tea per day
- 15% lower for those drinking six cups of tea per day.
Other studies have found even greater benefits. For example, in a study involving 38,000 women, those who drank at least 4 cups of tea per day were 27% less likely to develop type 2 diabetes than those who did not drink tea.
NB If you are on medication to lower blood glucose levels, and change the amount of tea you drink, check your blood glucose levels regularly and talk to your doctor about how to adjust your medication if your results improve (to avoid hypoglycaemia).
Tea and asthma
Tea contains substances (caffeine, theobromine and theophylline) that help to dilate the airways, plus antioxidant flavonoids such as quercetin and kaempferol which suppress allergic reactions.
Studies involving people with mild to moderate asthma found that, even at low doses, caffeine ingestion equivalent to a strong cup of tea appears to improve lung function for up to two hours after consumption, with improvements in peak flow (FEV1) of 12% to 18% after caffeine. Mid-expiratory flow rates also showed a small improvement which lasted for up to four hours. Other studies suggest that drinking tea two or three times a day might reduce the risk of asthma by 28%.
Tea and stress
Tea contains L-theanine, a unique amino acid that helps to reduce stress and promote relaxation. In a study involving over 42,000 Japanese adults, those who drank five cups of green tea per day had a 20% lower perception of stress or of experiencing psychological distress compared with those who drank less than 1 cup a day.
Tea and cancer
Studies have found that the powerful antioxidants in tea help to neutralise the harmful free radicals that damage cells and are linked with cancer. One tea antioxidant, epigallocatechin-3-gallate (EGCG), also activates specific proteins (SIRTs) within cells, which protect against cancer. Tea also contains a flavonoid polyphenol called kaempferol which has anticancer properties by reducing abnormal cell proliferation by arresting disordered cell cycles and triggering the programed cell death of abnormal cells.
High intakes of green tea (eight to ten cups a day) may reduce the risk of some cancers, especially those of the stomach, colon, rectum, pancreas, breast, skin and bladder, although this is not yet proven.
Tea and osteoporosis
Some studies have found that habitual tea intake can improve bone density and reduce bone loss to reduce the risk of hip fracture. Analysis of the results from 17 trials found that those with the highest tea consumption were 38% less like to be diagnosed with osteoporosis than those with the lowest intake. The studies involved observations of green tea and black tea intakes, with and without milk, so it wasn’t just the milk added to black tea that was protective, and the results were adjusted for alcohol and smoking habits.
Drinking tea could help you live longer
By protecting against age-related diseases such as heart attack, stroke and possibly cancer, tea may help you live longer. A study of more than 130,000 people, aged 18 to 95, found that even non-cardiovascular mortality was 24% lower in tea drinkers than non tea drinkers, over the seven year follow-up period. As well as enjoying better general health, physical activity levels also increased along with the number of cups of tea consumed per day.
Tea nutrition facts
Tea is also a good source of the trace element, manganese, and is one of the few dietary sources of fluoride. Three to four cups of tea per day, made with semi-skimmed milk, typically provides the following percentage of your daily needs:
- 45% manganese
- 25% vitamin B2
- 16% calcium
- 10% folic acid
- 10% zinc
- 9% potassium
- 9% vitamin B1
- 6% vitamin B5
- 6% vitamin B6
- 5% selenium
Green tea extracts
If you don’t like the taste of green tea, or don’t want to drink four cups of green tea daily, you could take a supplement supplying around 500 mg daily. Select one standardized to contain at least 50% green tea polyphenols and, ideally, at least 30% EGCG.
How to enjoy tea
Drink green, black or white tea regularly, three to five times a day. Use left-over cold tea to soak dried fruit, as a basis for sauces, soups or stews or to make ice cream. Matcha powder makes a great green tea ice cream, too.
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