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Green revolution

Many traditionally Eastern things are slowly gaining popularity in the West, like meditation, yoga, budget smartphones and of course: green tea. The tea plant, also known as Camellia sinensis (literally “Camellia from China”), has a rich history full of legends and myths. It is said that the first people who used it to brew a drink were warriors and monks, in appreciation of its stimulating effect. Slowly this practice has become more accepted in other parts of society, and nowadays green tea is famous around the world for its high antioxidant content and gentle alertness boost. But if you think that’s all it can do, you’re in for a big surprise.

Fig. 1: Green tea dust... don't breathe this!
Fig. 1: Green tea dust... don't breathe this!

What does it do?

Increases alertness and ability to focus and reduces tooth decay (only as brewed tea), provides anti-aging benefits, can help prevent cancer and infections, can improve cardiovascular health, reduce cholesterol and aid in weight loss.

Are there negative effects?

When drinking too much brewed green tea, a typical caffeine overdose can happen. Nausea and digestive troubles are possible from both tea as a drink and green tea extracts, but are much more common and stronger with extracts. For high doses of extracts (676 mg EGCG or more), liver toxicity has been recorded. No liver toxicity could be found for brewed tea in any amount.

How much should I take?

The sweet spot for most health effects seems to be a daily dose of 4 cups (1,000 ml) of tea, corresponding to 8g of tea leaves and 800 mg of catechins (of which 400 mg are typically EGCG). The upper safe limit for green tea extracts is 338 mg EGCG per day. There is no upper limit for brewed tea.

 

Health effects

Going green

In the West, tea is traditionally mixed with milk or sugar, and there is little focus on the taste of the tea leaf itself. In contrast, many Eastern countries have built a vibrant culture around the Camellia plant and have developed different techniques to grow, process and prepare its leaves. With many of these techniques, one can manipulate the amount of active substances in tea,[1-3] which are responsible for its unique flavor. The most popular of these substances is probably caffeine (slightly bitter), loved far and wide for its ability to increase alertness, focus and metabolic rate. A second compound called theanine (“umami”) further improves this focus boost by adding a relaxing effect, and it cancels out the blood pressure increase we would expect from caffeine – how convenient! The components that are responsible for the antioxidant powers of green tea are called catechins (bitter & astringent), of which about half are pure EGCG. These catechins potentially have a large influence on human health. Depending on the dosage, they can offer anti-aging benefits, improve virus defense, and even help prevent cancer. Furthermore, they can improve cardiovascular health, decrease blood cholesterol and help you lose weight.

Caffeine

– increases alertness, ability to focus and mental functioning[4]

– increases thermogenesis and energy expenditure[5]

– increases blood pressure[6]

L-theanine

– further improves the increased focus from caffeine[7]

– improves the ability to relax in a resting situation via direct action on the brain[8, 9]

– likely has a neuroprotective effect, helping to prevent dementia[10, 11]

– counteracts the blood pressure increase from caffeine[6]

Catechins (EpiGalloCatechin Gallate and others)

– exhibit antimicrobial effects that help protect from viral, bacterial and fungal infections[12-14]

– protect cells from free radical damage, indirectly reducing the effects of aging[15, 16]

– can potentially prevent cancer incidence by reducing DNA damage to cells[17]

– can keep early-stage cancers (prostate,[18] oral,[19] colorectal[20]) from progressing and kill tumor cells it comes in contact with[21, 22]

– help prevent tooth decay by affecting the mouth flora and reducing gum inflammation[23-25] (only as drink)

– improve cardiovascular health[15, 26]

– may increase fat oxidation and metabolic rate, probably depending on genetics and/or dosage[5, 27]

– may reduce blood cholesterol[15]

 

Side effects

Damn those jitters!

From its potent anti-aging effects to the alertness boost and a reduction in the risk of all-cause mortality,[28, 29] green tea looks like the perfect beverage. But nothing ever comes without a price. In the case of green tea, the price may be just that – however much you pay for your particular tea leaves. After all, studies found no long-term side effects even with high amounts of green tea consumed every day, and there is no hint for negative effects even in Eastern countries, where consumption is traditionally regular and high.[30, 31] Of course, you can still get some mild side effects from drinking green tea. If you take in too much at once, you could experience a caffeine overdose, meaning nervousness, irritability and trouble falling asleep, and possibly irregular or very fast heartbeat.[32] Drinking very strong green teas, especially on an empty stomach, can lead to feelings of nausea and mild digestive troubles.[33]

It’s a different story with the green tea extracts, commonly known as “green tea polyphenols”, “green tea antioxidants” or simply “EGCG”. These (usually decaffeinated) extracts are highly concentrated and are much more likely to cause nausea and other gastrointestinal distress, abdominal pain, diarrhea and indigestion. What is most troublesome is that they can be toxic for the liver when taken in high doses. Isolated cases have even led to liver failure, but it was never made clear if this was due to the extract, possible contaminants or pre-existing conditions.[34] So while the brewed drink seems comparably harmless, green tea extracts need to be treated with more caution.

Brewed (from whole leaf or powder)

– excess caffeine can induce nervousness, irritability and insomnia, as well as tachycardia and/or irregular heartbeat[32]

– especially when consuming a strong green tea on an empty stomach, nausea may result[33]

Green tea extract (commonly decaffeinated)

– high concentration of ingredients can cause nausea and abdominal distress such as pain, diarrhea and/or indigestion[33]

– can cause liver damage in high doses long-term[33]

 

Dosage

Getting your greens

If you’re ready and willing to put your newfound love for green tea into practice, two questions still remain: how much do you need, and how much is safe?

Most health effects of green tea seem to be strongly connected to the dosage. Unfortunately, not all studies use the same method of recording the daily dose. Some note the exact amount of EGCG down to the milligram, some only mention the total amount of green tea consumed in cups or liters. Looking at over 150 different studies, the average daily dose ranged from between 400-800 mg of total catechins (of which 200-400 mg EGCG). This corresponds to about 4-8 g of tea leaves (dry weight), or 2-4 cups (500-1,000 ml) of green tea per day.[33, 35] According to these numbers, one cup (250 ml) of green tea is prepared using 2 g of leaves, which contain 200 mg catechins, of which 100 mg are EGCG. These are rough averages that can vary in individual cases.

While a review on all-cause mortality also finds the sweet spot at around 4 cups per day,[29] some studies, especially those on weight loss[27] and cancer[19, 20] decidedly call for up to double that amount (800 mg EGCG or more). Because drinking 8 cups of tea a day is unrealistic for many people, this recommendation makes supplements very attractive. Unfortunately, the upper safe limit for extracts was calculated to be 338 mg EGCG per day, and liver toxicity was seen with amounts over 676 mg EGCG per day. This means that the optimal dosages for some health effects simply cannot be reached safely when taking a supplement. The best option therefore is also the tastiest: regularly brewing and drinking green tea. Alternatively, supplements can provide part of the benefits, but need to be handled with caution.

 

Frequently asked questions (FAQ)

Black tea contains different, but similarly effective antioxidants to green tea, and is a valid alternative,[36, 37] though it can’t be guaranteed to have the exact same effects.

Adding cow’s milk or plant milk is not recommended, as it may reduce the positive effect on the cardiovascular system,[35, 38] although the antioxidant activity is not reduced.[39]

 

Sources

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