Green tea: benefits, side effects and research

The most consumed beverage in the world is water – but right after that is tea! It’s easy to see why, as well; you can have it hot or cold, with blends ranging from English Breakfast to Earl Grey. About 84% of people consume black tea [1], but the second-most popular type of tea is green tea.

There have been plenty of studies done on the health benefits of drinking green tea, which traces its roots all the way back to ancient China.

These benefits include everything from lessening oxidative stress to aiding weight loss. And besides that, it tastes great!

So what makes green tea so good for our health and longevity? Here’s everything you need to know about green tea, from its history to its benefits and even the forms in which you can take it.

There have been plenty of studies done on the health benefits of drinking green tea, which traces its roots all the way back to ancient China.

History of green tea

“Green tea” is unoxidised tea and is made from the leaves of the camellia sinensis. After the leaves are plucked, they are allowed to wither slightly, then immediately steamed to preserve the green quality. This process prevents oxidation, which allows a higher concentration of chlorophyll and antioxidants.

Green tea is either sun-grown or shade-grown, which can affect the flavour.

Written records trace the production and consumption of green tea all the way back to China’s Han Dynasty (209-220 AD).

Its primary use in ancient times was medicinal, such as aiding digestion or healing wounds. It wasn’t until the Tang Dynasty in 600–900 AD that green tea became consumed purely for taste and pleasure.

During this dynasty, a Chinese scholar named Lu Yu released a book about the art of drinking green tea, called “The Classic of Tea.” It thoroughly explored the plant and its preparation, as well as the culture surrounding it. 

The Chinese also developed a tea ceremony – a ritual preparation of the drink. Because the tools of this ceremony were generally available only to the wealthy, the consumption of green tea became a status symbol.

It took until the late 19th century for tea to reach western cultures, specifically Europe. Freshly-harvested green tea was difficult to come by due to transport issues, and so only “cooked” black tea was available.

But the innovation of clipper ships shortened the time it took to transport supplies, meaning that green tea reached European countries. [2]

These days, green tea is widely available all across the world in various forms, from loose leaf to powdered. It’s even used as a flavouring in pastries.

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Green tea nutritional value

A single 16oz (473ml) serving of green tea contains 0 calories – so 0g fat, 0mg cholesterol and 0g carbohydrates. It does contain 33.1mg of sodium, but no proteins. Green tea does contain some calcium, phosphorus, potassium and zinc. The drink consists mostly of water.

Of all teas, green tea contains the most antioxidants since it is mostly polyphenols. [3]

Does green tea have caffeine?

In terms of caffeine content, green tea has 56.8mg of caffeine per 16oz – versus 94mg in black tea and 181.4mg in 16oz of coffee. [4]

Forms of green tea

You can find green tea in various forms, such as:

  • Bottled drinks (sweetened or unsweetened)
  • Tea bags
  • Loose leaves
  • Powder (matcha)

Health benefits of green tea

There has been promising research into the health benefits of green tea due to its high polyphenol content. Consuming 2–3 cups (so about 24oz or 709ml) of green tea a day has associated boosts to our well-being.

Beyond these listed benefits, the National Center for Complementary and Integrative Health (NCCIH) is funding research into green tea and its influence on conditions such as inflammatory bowel disease and high cholesterol [5].

1. Metabolism

Some research shows that green tea can actually help you slim down – consuming about 4 cups of green tea daily can cause a decrease in body weight. 

The leaves are excellent sources of epigallocatechin 3-gallate (EGCG), which has a positive influence on your body’s ability to process glucose and manage your weight. It also boosts the way your body metabolises and oxidises fat. [6]

Some research shows that green tea can actually help you slim down – consuming about 4 cups of green tea daily can cause a decrease in body weight. 

2. Inflammation

EGCG doesn’t just influence your body’s metabolism – it also has anti-inflammatory effects. Topically-applied tea extracts can reduce inflammation on your skin, while consuming it has a much more subtle effect. [7]

3. Antioxidants

Green tea has high levels of polyphenols or flavonoids, which act as antioxidants. These antioxidants work to combat oxidative stress in our bodies caused by free radicals, which alter DNA and damage our cells. 

Our body produces free radicals naturally through cell metabolism, but we can pick up excess amounts from external sources such as pollution or medication.

An accumulation of excess free radicals leads to “oxidative stress.” This plays a significant role in the development of age-related degenerative illnesses such as cancer and arthritis.  [8]

4. Cardiovascular health

There are few long-term studies, but many suggest that the antioxidants in green tea can help lower high blood pressure and cholesterol levels, which reduce your risk of developing adverse cardiovascular conditions. It may even be that consuming 5 cups of green tea a day can reduce your risk of mortality through a cardiovascular condition by 26% [9].

5. Cognitive function

Some analyses suggest that drinking tea daily – especially green tea – decreases your risk of cognitive impairment [10]. There has also been research into how green tea can enhance a person’s memory and thinking process [11].

Green tea is also a source of caffeine, which acts as a stimulant. This makes you feel more energised and alert, which can indirectly improve brain function.

6. Cancer prevention

Cancer rates tend to be lower in countries that have high rates of green tea consumption, but that link is mostly a correlation.

Still, some research has shown that tea polyphenols may help prevent UVB-induced skin cancer by protecting the skin from UVB radiation. This is why some sunscreen products include green tea in their ingredients [12].

Some test tube studies have also suggested a positive impact of green tea on cancer of the breast, bladder, ovaries, lung and stomach [13].

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Side effects of green tea

There are few known side effects linked to consuming green tea in healthy adults. However, there are some risks, especially when consumed in large amounts. [14]

1. Caffeine sensitivity

For people especially sensitive to caffeine, the amount found in green tea – particularly when someone consumes multiple cups – can cause adverse effects such as

  • Anxiety or jitteriness
  • Irritability
  • Insomnia
  • Nausea
  • Upset stomach

2. Liver conditions

In rare cases, a high concentration of green tea or green tea extract could have adverse effects on your liver.

3. Concurrent consumption

Since caffeine is a stimulant, if you consume green tea alongside other stimulating substances such as prescription medication, you may experience an increase in blood pressure and heart rate. It may also cause symptoms of anxiety.

You can brew green tea leaves on their own, but many people prefer to drink tea blends. These blends have a more complex flavour that makes them enjoyable to consume. [15]

1. Jasmine

High-quality green tea leaves are imbued with the scent and flavour of jasmine flowers. Jasmine green tea is a popular tea that has a sweet, floral flavour. Prepare jasmine green tea by using water that has just been simmered, not boiled. Infuse for only a few minutes for a light and refreshing taste.

2. Mint 

Mint tea is a common choice of drink, but Moroccan Mint green tea is a favoured blend. It comes from a mix of Chinese gunpowder green tea and fresh mint leaves, which are boiled together in hot water. You can also use other forms of green tea or mint to taste.

3. Sencha

Sencha is the most common form of green tea found in Japan. It has a grassy sort of flavour, which can quickly turn bitter if you brew it with too-hot water. The brewing time depends on the type of sencha. You can enjoy sencha hot or cold, and sweetened or unsweetened.

4. Lemon and honey

Lemon is a popular addition to many teas since its astringence adds depth to their flavours. Honey is also a popular sweetener. Adding both to green tea produces a taste that’s both citrusy and grassy.

Green tea vs. matcha

Matcha is a form of green tea that has been ground into a fine powder. You take young leaves and turn them into matcha through a specialised process.

While most places now use machines to grind the tea leaves into powder, ceremonial-grade matcha – the highest grade in Japan – is still often made by hand using a stone grinder.

Matcha comes from green tea plants that have been kept under shade, which increases the chlorophyll content in the leaves.

This gives them a lighter, brighter green colour and increases their nutrient content. Matcha as a drink has a more concentrated taste than regular tea leaves brewed in water [16].

The matcha tea ceremony is highly valued in Japanese culture. It is a ceremonial or ritualistic way of preparing the tea, from pouring the water to whisking it to serving it.

Previously, only monks or nobility would perform the tea ceremony, but nowadays it’s even become a popular tourist attraction [17].

Matcha is a form of green tea that has been ground into a fine powder.

Other forms and uses of green tea

You can find green tea in food and beverages beyond plain brewed tea. Here are some other forms and ways people use green tea in their everyday life.

1. Supplements 

Green tea extract is a concentrated form of the original beverage. One capsule can contain the same active ingredients as you would get from one cup of green tea, with all the same benefits. You can also find it in a liquid form [18].

2. Mixed drinks

Beyond the usual plain beverage, it’s become popular to mix matcha into different drinks. Matcha milk tea is exceptionally popular. Boba and coffee shops, as well as restaurants, serve this drink made from matcha powder, milk and a sweetener. 

3. Pastries and sweets

People add matcha to all sorts of desserts now – cakes, brownies, fudge, cookies and even cheesecake! The powder is also frequently sprinkled on top of baked goods to add flavour and a slight bitterness. 

You can also add matcha to chocolate.

Green tea and longevity

Given its high antioxidant content and benefits to our well-being, green tea is possibly one of the healthiest drinks you can consume.

Its association with lowered risks of cognitive and cardiovascular issues also means it can boost your longevity. Indeed, green tea could help lower your risk of mortality and help you live a little longer [19].

Much like there are “superfoods” such as avocado, green tea may be considered a “super drink” since it’s so good for our health. It also tastes great and provides you with refreshment, making it a wise addition to your diet.

Get the kettle on!

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Photograph: Mareefe/Pexels
The information included in this article is for informational purposes only. The purpose of this webpage is to promote broad consumer understanding and knowledge of various health topics. It is not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of your physician or other qualified health care provider with any questions you may have regarding a medical condition or treatment and before undertaking a new health care regimen, and never disregard professional medical advice or delay in seeking it because of something you have read on this website.