What scientists tell us about tea

Tea is recognized and appreciated by cultures around the world for its capacity to balance, soothe, restore, and refresh; in fact, the first Japanese tea manual, written by the famous Zen buddhist Eisai in 1211, asserted boldly that

Tea is the ultimate mental and medical remedy and has the ability to make one's life more full and complete

white tea

Throughout the world, and especially in China and Japan, tea is considered as an elixir of life since it was discovered by the legendary emperor and originator of the Chinese herbal medicine Shen Nong some 5000 years ago. The drink, that is produced from the plant Camellia sinensis, has an impressive list of health benefits, with more and more evidence surfacing in modern times, providing deeper understanding and support for traditional knowledge and applications.

In this here blog post, I’d like to look a little more closely into the research side of things. In other words, what do scientists claim to know about the health benefits of tea?

It's all in the Leaf...

“Tea contains over 2,000 components, including polyphenols, pigments (carotenoids and cholorophyll) and alkaloids (caffeine, theophylline, theobromine), lignans, carbohydrates, lipids, proteins, amino acids (including L-theanine), vitamins (vitamin C, vitamin E, riboflavin), and various minerals and trace elements.” [Linus Pauling Institute, Micronutrient Information Center – Tea]

A lot of things are happening within a tea leaf. I mean, just look at the vast number of different tea types, all derived from one plant species: Camellia sinensis.

Quality and type of tea is determined by the presence or absence of chemical compounds which are formed during plant growth and leaf processing. These compounds impart color, taste, brightness, strength and flavor in the infusion. For example, polyphenols are derived from amino acids via sunlight. These health beneficial substances are largely responsible for astringency in the cup. To the contrary, if a tea is grown in a shady place, the amount of amino acids is increased and the tea has therefore a stronger umami taste. If the tea leaf is exposed to oxygen (air) after picking, its chemistry is drastically changing, resulting in altered taste and color of the tea due to enzyme activity, pigmentation,  and so on…

Let’s list some of the major compounds in tea, and focus on their benefits without wandering off track too much.

Antioxidants / Polyphenols

The major interest in tea and health stems from the high level of antioxidant tea polyphenols in Camellia sinensis, which can be estimated as much as 30-40% in the dry leaf matter. Tea plants synthesize polyphenols as part of their natural defense mechanism to deter leaf eating predators, such as insects and other animals (well, humans excluded).

Antioxidants are certain substances that are commonly regarded beneficial for our health and well-being; they are cancer protective, boost immune function, anti-aging, the list goes on. But unlike other nutrients, such as vitamins and minerals, the term antioxidants is often shrouded in mystery. Who is oxidizing? When? Why? I thought Oxygen is essential to life? Are you pulling my leg?

So before we talk about a group of nutrients pigeonholed as Antioxidants, we would require some background information to see how things play together, i.e. why our body needs to counteract Oxygen reactions, and to what extend.

Oxygen, as we know, is essential for us to generate energy from food through the process of respiration:

glucose + oxygen → carbon dioxide + water + energy

This process involves the transfer of electrons (energy containing particles) in order to produce ATP (Adenosine triphosphate), which powers most cellular reactions. Occasionally electrons escape, and instead of completing the cellular respiration cycle, are transferred to an Oxygen molecule, thus forming Reactive Oxygen Species (ROS), aka free radicals. These free radicals are unstable particles, and therefore highly reactive. In order to stabilize themselves, they are now stealing electrons from neighboring substances, making them unstable in return, and so forth – a chain reaction occurs, that quickly wreaks havoc on living tissue including DNA/RNA.

Besides being produced during normal cell metabolism there are numerous exogenous factors, such as irradiation by UV light, drinking alcohol, heavy metals and atmospheric pollutants which may lead to generation of free radicals.

So, how can we fight these radicals ?

(we attack them verbally! er…. No, you still with me, are you?!)

The human body utilizes both endogenous antioxidants, such as enzymes and hormons, and dietary antioxidants, i.e. vitamins and polyphenols, as its defense mechanism. These substances neutralize free radicals by accepting or donating electron(s); basically they work as a buffer and are able to restore balance. A well working antioxidative system is therefore essential for our body to prevent cell dysfunction, inflammation, cardiovascular disease, cancer, diabetes, Alzheimer’s disease, cataracts, autism and aging.

“Several studies show that polyphenolic compounds present in tea reduce the risk of a variety of diseases. Research findings suggest that the polyphenolic compounds, (−)-epigallocatechin-3-gallate found primarily in green tea, and theaflavin-3,3′-digallate, a major component of black tea, are the two most effective anti-cancer factors found in tea.” [Life Sci. 2007 Jul 26; 81(7): 519–533.]

Flavonoids comprise the majority and most important group of (antioxidative) polyphenols in tea leaves. They are also referred to as Catechins (prevalent in green tea) and Tannins (mostly prevalent in black tea).

In terms of health benefits – Green tea versus Black tea, there are benefits associated with drinking any type of (quality) tea. So, firstly, it would come down to taste preferences and life style choices. However, when we compare the antioxidative potential of the two types, Green tea is considered to have a greater effect.

But not only the type of tea matters; interestingly, water temperature, tea quality, and the addition of milk to (black) tea can also affect antioxidant properties:

“Preparation of teas across a range of temperatures between 20 and 90 degrees C revealed that although antioxidants were liberated from the leaves into the water in cooler infusions, increasing the temperature could increase antioxidant potential by 4 to 9.5-fold. Black tea prepared using tea bags had significantly lower antioxidant capacity than black leaf tea at temperatures between 20 and 70 degrees C, suggesting that tea bag materials may prevent some extraction of flavonoids into the tea solution. The addition of milk appeared to diminish the antioxidant potential of black tea preparations. This effect was greatest where whole cow’s milk was used…” [Int J Food Sci Nutr. 2000 May;51(3):181-8.]

As usual in science, there are other studies finding exactly the opposite: “it [the addition of milk] did not affect the beneficial effects of black tea on total plasma antioxidant activity…” [Ann Nutr Metab. 2005 May-Jun;49(3):189-95. Epub 2005 Jul 13.]

There’s a lot (controversial) information out there addressing the “milk-question” alone. Might be some food for thought in a future post! But let’s move on for now…

Amino Acids

Yes, the building blocks of proteins, i.e. muscles, cells, and other organic tissues. It is estimated that there are about 1-6% amino acid in tea leaves (dry matter). Levels are specifically high in shade-grown tea types, such as Japanese powdered tea (Matcha) or Gyokuro green tea, which gives these types their typical umami taste. The most abundant amino acid in the leaves is L-Theanine, which has reported psychoactive properties.

In our modern world, we usually try to identify single substances that are responsible for a specific effect. Well, L-Theanine is believed to cause most of the positive mood altering phenomenons.

Personally, I think its a combination of the pleasure of drinking a great cup of tea itself that causes joy and happiness – sure and then there is the slow release of caffeine in combination with L-theanine putting the cherry on the cake.

“L-theanine, at realistic dietary levels, has a significant effect on the general state of mental alertness or arousal.” [Asia Pac J Clin Nutr. 2008;17 Suppl 1:167-8.]


A group of alkaloids with a mildly stimulating effect. In tea, we would find predominantly caffeine, and theobromine and theophylline in smaller quantities. Caffeine is widely used to enhance alertness and improve performance. It also seems that the combination of Caffeine and the previously mentioned amino acid L-Theanine may have some synergistic effects. Different studies found a greater improvement in speed, accuracy, memory and alertness when both substances were taken together instead of isolated.

Read more about the effects of Caffeine (and L-Theanine) in tea in my previous blog post.

Theobromine (from the greek meaning theo = god, broma = food “Food of the Gods”) is a bitter alkaloid mainly present in the cacao plant, but also in tea. It is a precursor to caffeine, which suggests that its psycho stimulating effects are caffeine-like, but milder. There’s some evidence out there showing its ability to dilate blood vessels, so it may be useful to treat high blood pressure. It also has a diuretic effect, and in high dosage it might improve oral health.

As expected, impacts of Methylxanthines on our body in general are largely dose dependent.

I summarized Methylxanthine concentrations of tea in comparison to coffee and chocolate in table 1 below:

  Caffeine Theobromine Theophylline
Black Tea 200ml 71 mg 3.6 mg <1
Green Tea 200ml 43 mg 0.7 mg
Espresso 70ml 532 mg
Dark Chocolate 100g 0.31 mg 1.16 mg 9 mg

Table 1: Sources of Methylxanthines in diet
[Molecules. 2016 Jul 27;21(8). pii: E974. doi: 10.3390/molecules21080974.]

And here (table 2) is a short summary of the effects of Methylxanthines on our body, and to what degree:

  Caffeine Theobromine Theophylline
Brain stimulation +++ + ++
Respiratory Stimulation +++ + ++
Diuresis ++ + +++
Cardiac Stimulation + ++ +++
Skeletal Muscle Stimulation +++ + ++

Table 2: Effects of the naturally available methylxanthines ranging from more potent (+++) to less potent (+)
[Molecules. 2016 Jul 27;21(8). pii: E974. doi: 10.3390/molecules21080974.]

Carbohydrates, Minerals and Vitamins

There are about 10% of carbs/sugars in dried tea leaves, which (you guessed it) are responsible for the natural sweetness in the infusion, making tea a delightful drink that doesn’t require added sugars or other additives.

Furthermore, tea contains 5-7% minerals, mainly potassium (nerve and muscle function), calcium (bone health), phosphorus (growth and cell function), and magnesium (enzyme activity, cell signaling), as well as small quantities of manganese (bone health), zinc (immune function, skin health), Fluorine (oral health) and copper (energy production).

On the vitamin side we can list Vitamin B2 (energy production), Vitamin C (immune function, collagen production, antioxidant), Folic Acid (formation of red blood cells), β-carotene (precursor of Vitamin A, healthy vision, bone growth), Vitamin E (antioxidant, anti-aging). Among others…


So there...

…and I am just touching the surface. It’s amazing, the more you read the more you learn. Tea has been the subject of thousands of studies. Of course, there will be different findings, different outcomes, different objectives, controversial results; sometimes it sounds all so incredible positive, then some draw backs, then something completely out of the blue – welcome to the world of science. I hope I didn’t fry you too much. Bottom line is this, tea is one wild drink 🙂

A true gift of nature. And…

…while it is intriguing to explore some of the broad health benefits of Tea, it is the quietness and harmony in the leaves that reveal the greatest blessing for body, mind and soul. Through tea, we learn to listen to the unfolding moment, and we realize that even the flavor of the liquor is as much dependent upon the skill of the one brewing as the quality of the leaf.

2 replies on “What scientists tell us about tea

  • Michelle

    Was just reading the history of tea in my herbal book, you might also find it interesting. According to legend, one of China’s first Emperors, Yan Di (2852-2737 BCE) is said to have discovered tea after having poisoned himself while testing other herbs. As he fell to the ground dying, a dew drop fell from a tea leaf into his mouth and cured him instantly. The rest is history 😉
    Glad to read that it’s so super duper healthy too! Great article.

  • Sensado

    Great comment. Thanks Michelle! I just read that “An academic conference held in China in 2004 achieved general consensus that the Yan Emperor and Shennong were the same person.” In other texts, Lu Yu, a famous Tang monk who excelled in the culture of tea, and Shennong are referred to as one and the same. However, the emperor begun to use tea as a remedy; and only ‘later’ during the Tang Dynasty (618–907 CE), tea evolved more and more into a drink of pleasure. Thus linking the benefits for body, mind and soul…


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