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Exploring the benefits of tea : Blog 2 : The Chemistry of Tea & Health

Throughout the months of January & February we are exploring themes around tea & wellbeing.  Every Monday in January Michelle & Camille came together to discuss gentle resilience on our IGTV and, linked to this I, Rob, am exploring the incredible tea plant & how the tea leaf & tea, the drink, can be a major positive in our lives.  My blogs will explore the the benefits of tea through three lenses : Ritual, Chemistry & Community.  I hope you enjoy these short explorations.  


From the first leaves that supposedly saved Shennong’s life all those years ago to modern-day medicine, tea has always been known for its health-giving properties. Chinese medicine has always recognised the usefulness of the tea plant, but its qualities have not been proven in science until relatively recent times. There are now a great many scientific papers on the subject, as well as all sorts of more spurious benefits used as marketing tools. Studies have increased as the understanding has grown that nutrition can have a much larger impact on health and in particular mental health.
However, there is still a lot of work to be done on the identification of  the major active compounds that give tea its physical and mental-health benefits, including whether they work alone or in combination with other compounds present.

In our last blog we looked at how the ritual of taking tea can be a major benefit on its own, in particular in lowering the stress hormone cortisol. A recurring feature I have found researching this post is the recognition by the best researchers in this field that an awareness of;  the affect of ‘just taking tea’ ; is key to proper conclusions.   If the researcher does not pay correct attention to this or attempt to explore this element of tea and consider this in their conclusions then any health benefits can be over stressed, leading to a serious clouding of the science [beautiful photo below credited to Maria Madison photographer]

At Comins we focus on the experience, ceremony and taste of taking tea rather than on drinking tea for health, but we are of course interested in the properties of the plant itself. The main benefits are listed below, and we encourage you to take them as an introduction to further reading and research [over a cup of tea of course!]

The tea leaf is made up of many different compounds or groups of chemical substances, the most prevalent ones being polyphenols. These can be up to 40% of the leaf’s dry weight and provide a significant portion of the health benefits found in tea; namely antioxidants. They are also largely responsible for the astringency in the taste of tea. Other health giving compounds found include minerals, vitamins, amino acids, caffeine and other methylxanthines as well as hundreds of aroma compounds in trace amounts. Of course all of the above are extracted from the leaf by adding the dried leaf to hot water and infusing. Water is often overlooked!


Antioxidants are contained in flavanoids, a category of the polyphenols mentioned above and have been linked to the possible prevention of things like cardiovascular disease, cancer, blood pressure, as well as delaying the ageing process and increasing vitality. They do this by countering the harmful effects of ‘free radicals’, naturally occurring unstable molecules that, if present in large amounts, can damage cells in our bodies. Many studies have shown that flavonoids are the most effective antioxidants found in nature.

The most common type of flavanoid in tea are Flavan-3-ols (commonly called flavanols), which contain catechins (often incorrectly referred to as tannins). The major catechins in tea are catechin (C), Epicatechin (EC), epicatechin gallate (ECG), gallocatechin (GC), epigallocatechin (EGC) and epigallocatechin gallate (EGCG). Of these EGCG is the focus of most studies, as it is the most active and may have cancer-fighting properties. It is said to be one of the most powerful antioxidants known. According to Nature | Outlook [ref 1Nature | Outlook] EGCG is thought to “make people feel calmer and improve memory and attention when consumed on its own”EGCG is also fairly simple to extract and use for pharmaceutical purposes and is continually being researched and refined. 

Catechins are especially plentiful in green tea [such as Sencha Fukamushi pictured below] as the particular processing method (fixing or ‘kill green’)  halts the action of any oxidising enzymes which would reduce the amount. 

When catechins are oxidised by these enzymes in black or oolong tea processing (oxidation) [see the tea Ruby Black pictured below] they are converted into complex catechins, such as thearubigins and theaflavins.  These are usually described as providing  the dark-brown and orange-red colours and more robust flavours of these teas, but recent research has suggested that they offer similar antioxidant benefits as green tea. Many studies mention particular positive effects on gut health, blood pressure, cholesterol and anti-cancer.

The flavanoid group also contains anthocyanin. These are found naturally in a number of foods, and are the pigments that give red, purple, and blue plants their rich colouring. In tea this means purple tea, cultivars of which have been grown in India, China, Sri Lanka and are recently Kenya. As with other flavonoids anthocyanins may offer anti-inflammatory, anti-viral, and anti-cancer benefits.


There are plenty of vitamins & minerals packed naturally into the tea plant. Most teas are very good sources of vitamin C, a very strong antioxidant. Vitamins B1, B6 and also carotene, which is turned into vitamin A by the body, are also present. These all have antioxidant qualities. Minerals such as manganese, potassium and fluoride can also be found. Manganese is key for bone growth, potassium aids the heart and fluoride the teeth. Of all of these manganese is found in a higher concentration in brewed tea compared to that of other foods, so will make more of a significant contribution to the average daily intake.


Methylxanthines make up between 3-5% of the dry weight of tea leaves. They are partly responsible for the bitterness of the tea leaf as the plant creates them to make its taste undesirable to insects and animals. Caffeine is the major methylxanthine alkaloid found in tea. It is a stimulant and despite its usually negative reputation, caffeine does have benefits. It promotes digestion and cardiac function and can be known to help weight loss by promoting digestion.  You can read more about Caffeine in our earlier blog

Other methylxanthines found in tea are theobromine and theophylline. Theobromine is a mild stimulant and has been shown to lower blood pressure. It also may help in suppressing coughs. Theophylline has similar benefits, like the potential to improve blood flow and make breathing easier and. In fact,  interestingly, Theophylline is used to treat asthma, albeit with much larger amounts than that found in tea.


The proteins in tea leaves are made up of amino acids. One of the most abundant is L-theanine as it accounts for almost half of the total free amino acids found in tea. It is responsible for the full bodied, umami savouriness and sweetness in teas [many people comment on this in Japanese teas such as the Sencha Karigane pictured below] and is only found in one other plant and one type of mushroom.

The main health benefit of
L-Theanine is that increases relaxation by stimulating alpha-wave production in the brain. In the long term it is said to reduce psychological stress, improve the memory and aid against viral infection by improving the immune system. L-theanine slows down the release of caffeine from brewed tea into the body. The short-term effect of this is to create a feeling of controlled stimulation that can last for a long period of time. This ‘mindful alertness’ is what first drew monks to tea, who found it useful during long meditation sessions.

This relationship between L-theanine and caffeine is examined in an article in Nature2 [see references at the bottom of this page], which states that alongside the above, consuming L-theanine with caffeine improved memory and reaction time to a greater extent than if each was consumed on its own.


There are hundreds of aromatic substances in tea, which we notice mainly in the flavour and aroma of the tea. However, they can have a deeper impact as painkillers with anti-bacterial and anti-inflammatory affects. They can also promote relaxation through their soothing nature.


Water makes up nearly two-thirds of a man's body and just over half of a woman’s. To keep this at the correct level most adults need about 2 to 2.5 litres of fluid a day, equating to around 10 cups. The fact that brewed loose leaf tea taken without milk or sugar has no calories, and it is usually around 98.5% water means that tea is a great way to achieve this hydration. However, the role of water does not stop simply with hydration.

In Tang Dynasty (900BC) China, Lu Yu wrote in the “Cha Jing”, or “Classic of Tea”, that the best water for brewing tea came from the centre of a swiftly moving mountain stream. Most of us don’t have access to swiftly moving mountain streams but finding the right source of water is very important, both for achieving the best flavour and also because it has an affect on extraction of the beneficial compounds mentioned above.

A study2 [see references at the bottom of this page] into using bottled, tap and ionised water to brew tea concludes that ‘for tea drinkers consuming green tea for either flavour or its health benefits, our results highlight that the type of water used to brew tea is clearly important, and suggests that those seeking greater health benefits should use a more purified water source to brew green tea, while those more concerned with flavours may prefer to use water from the tap’. This is certainly an area for further exploration.


Every tea contains different levels of the compounds mentioned above, and certain types are linked with certain health properties. Processing brings out, decreases or changes these properties
White tea
, being the least processed and containing more antioxidant-rich leaf buds than the other types, has a high concentration of antioxidants, making it great in fighting illness. White tea is also calming in nature.

Green teas have similar amounts of antioxidants to white tea, as well as a wider range of polyphenols, which are especially good at countering the effects of free radicals and therefore lowering the incidence of cancers. Green tea has also been shown to lower blood pressure and improve cholesterol, thus protecting against heart disease.

Oolong tea is known to aid digestion because its properties stimulate the metabolizing of lipids. This is why oolong tea is often irresponsibly touted as a ‘slimming tea’. As with all health claims, it must form part of a suitable health programme.
Black teas have been shown to lower blood pressure and protect against heart disease due to their higher levels of theaflavins.

Finally, dark or puer teas have a history of being used to aid digestion, particularly in the nomadic tribes of Asia whose diet involved the rich meat of yaks. They also are known to reduce bad cholesterol and raise good cholesterol. 

The variations within each type of tea are enormous, so health benefits can only ever be generalized. Add to this the variation in biology of each tea drinker, and how this controls the absorption or effect of each compound, and it is obvious why tea and health is such a tricky subject. Certainly there is much to gain from tea if we allow ourselves the time to get to know it but, as with many aspects of tea, these beneifts are still not fully understood.


1Nature | Outlook - 7 Feb 2019 / Vol 566 / Issue No 7742, Tea by Herb Brody

 2The Influence of Water Composition on Flavor and Nutrient Extraction in Green and Black Tea, Melanie Franks, Peter Lawrence, Alireza Abbaspourrad, and Robin Dando*

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