What you need to know about Tea Part 1: Tea Varieties and Health Benefits
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I adore tea! And I’m not alone: tea is second only to water as the world’s most-consumed beverage.
Varieties of Tea
There are five main varieties of tea, all produced from the plant Camellia sinensis, and differing according to how they are cultivated, when they are picked and how they are processed after harvesting.
White Tea: White tea is prepared from very young leaves or new growth buds covered with tiny, silvery hairs. It is harvested only in early spring and is steamed (Japanese style) or baked/roasted (Chinese style) and dried immediately after harvest to preserve its polyphenol content by deactivating the enzyme polyphenol oxidase (more on polyphenols below). White tea has the lowest caffeine content of all tea varieties (approx.15-30mg per cup, depending on how much is brewed).
Green Tea: Green tea is made from more mature leaves than white tea, but is also is produced in a way to minimise oxidation of its polyphenolic compounds. So as with white tea, green tea leaves are immediately steamed or dry cooked in hot pans to deactivate the action of polyphenol oxidase. Because oxidation is kept to a minimum, the leaves retain their green colour, as well as much of their polyphenol content.
The health-promoting effects of green tea are mainly attributed to its polyphenol content, which includes flavanols, flavandiols, flavonoids, and phenolic acids. The major flavonoid phytochemicals in green tea are various catechins. In green tea, the four main catechins are epicatechin, epigallocatechin, epicatechin-3-gallate, and epigallocatechin gallate (EGCG), which have been shown to have antioxidant and anti-inflammatory properties.
Studies have shown that green tea may have a protective effect against cancer, type 2 diabetes, heart disease, stroke, tooth decay and osteoporosis.
Matcha: Matcha is a variety of green tea that has its origins in Japan. The tea plants are covered for 3 - 4 weeks prior to harvesting to block sunlight. This boosts the tea’s chlorophyll (green pigment) levels. It also changes the flavour profile of the tea, giving it a grassy, less astringent, almost sweet flavour. As with green tea, harvested leaves are immediately steamed to prevent oxidation, then laid out flat to dry. Once dried they are de-stemmed and finely ground into a bright green powder. Matcha is traditionally prepared by whisking the matcha powder in hot, but not boiling, water (approx. 70°C).
While there are lots of studies investigating the health benefits of black tea, and even more on green tea, matcha has not been studied to the same extent.
One difference between matcha and the other tea varieties is that you are consuming the whole leaf rather than just an infusion, so you will necessarily be consuming more of the tea’s phytonutrients. In fact, a cup of matcha can contain up to three times the amount of the flavonoid catechin EGCG as normally brewed green tea.
Black Tea: A key difference between black and green tea is that with black tea the harvested tea leaves are specifically treated in a way which promotes rather than hinders their oxidation. The harvested leaves are dried, rolled and then crushed to maximise oxidation via the operation of the polyphenol oxidase enzyme. As a result, the polyphenol compounds (catechins) in the tea leaves are dimerized and transformed to into complex tannins, a variety of theaflavins. This oxidation process doesn’t necessarily rob tea of it’s health-giving benefits, but because it’s phytonutrients have been transformed, we do see a slightly different set of protective effects. Studies indicate that black tea consumption may protect against hypertension, heart disease, stroke, type 2 diabetes, lung disease and neurodegenerative diseases. Black tea is also highest in caffeine, containing approx. 25-45mg of caffeine per cup, depending on the strength of the brew.
Oolong Tea: Oolong tea sits mid-way between green and black tea in terms of oxidation. The harvested tea leaves are usually withered under the influence of sun and warm winds, resulting in lower levels of oxidation.
Different varieties, all from the same plant
So all of the above varieties of tea come from the same plant, Camellia sinensis, but their taste and phytonutrient content differs according to how the fresh tea leaves are cultivated, harvested and treated after harvesting. The following diagram (from this study) shows how the different processing techniques impact the balance of Catechins versus Theaflavins and Thearubigins.
Image ref: Cooper R, Morré DJ, Morré DM. Medicinal benefits of green tea: Part I. Review of noncancer health benefits. Journal of Alternative & Complementary Medicine. 2005 Jun 1;11(3):521-8.
So what exactly is in Tea?
The “hero ingredient” in tea is its high content of biologically active phytonutrients, including an array of flavonoids and other polyphenols, which can comprise up to a third of its weight. As seen above, if the tea leaves are allowed to oxidise, they will lose their green colour and their catechins will convert to Theaflavins and Thearubigins. But if the freshly harvested leaves are heated after harvesting, oxidation will be minimised and their catechin content will be preserved.
In addition to phytonutrients, tea also contains proteins (enzymes and amino acids theanine, glutamic acid, tryptophan, glycine, serine, aspartic acid, tyrosine, valine, leucine, threonine, arginine, and lysine), carbohydrates (cellulose, pectins, glucose, fructose, and sucrose), minerals and trace elements (calcium, magnesium, chromium, manganese, iron, copper, zinc, molybdenum, selenium, sodium, phosphorus, cobalt, strontium, nickel, potassium, fluorine, and aluminium), and tiny amounts of omega-3 and -6 fatty acids, sterols, vitamins (B, C, E), as well as caffeine, chlorophyll and carotenoids.
The quality and chemical composition in the tea you drink is influenced by the quality and composition of the soil in which it is grown, what is applied to the tea while it is growing (rain, irrigation water, pesticides, fungicides, air pollution) and how it is processed and packaged and transported (more on that in Part 2 of this series, next week!).
Health Benefits of Tea
When it comes to health benefits, green tea is the clear winner, although studies confirm numerous health benefits from consumption of black tea too.
It can be challenging to scientifically identify a cause-and-effect relationship between the foods we eat and various disease states. That’s largely because food and lifestyle-related diseases can take decades to manifest.
There are lots of high quality epidemiological (population) studies which show clear links between tea consumption, better health and lower incidence of disease. These studies follow large groups of people over time. But epidemiological studies can’t determine rock-solid cause-and-effect relationships, only associations. So while scientists know there is a link between tea consumption and better health, at this stage it isn't clear exactly how potent tea’s health benefits really are. Is it the case that people enjoy better health and lower disease rates because of their tea consumption, or is it is simply the case that people who drink tea make healthier overall nutrition and lifestyle choices? We’ll know for sure in time, but for now the good news is that the epidemiological studies are also supported by lab studies looking at components in tea including its catechins, as well as a small number of intervention trials.
This is what we know so far about the health benefits of tea:
Anti-inflammatory effect: green tea in particular has been noted to have an anti-inflammatory effect via the impact of its catechins on a number of pathways, including downregulation of inflammatory cytokines, chemokines, and inflammatory markers and C-reactive protein (CRP). I’ll be writing a lot more about inflammation and anti-inflammatory nutrition soon. Chronic inflammation has been linked to an array of serious health issues, which is why there is so much interest in the anti-inflammatory effects of green tea.
Antioxidant effect: the polyphenols in tea have been shown to have an antioxidant effect in the body. Cells under oxidative stress produce reactive oxygen species (aka free radicals) which can cause a chain reaction of cell and DNA damage. As with inflammation, excessive oxidation is a known disease (and ageing!) pathway. The polyphenols in tea they can dampen-down this free-radical chain-reaction.
Cardiovascular health: in addition to its anti-inflammatory and antioxidant effect, tea has also been shown to have a beneficial impact on platelet aggregation (and therefore arterial clotting) and lipid metabolism. Tea consumption is associated with lowered LDL ("bad") cholesterol, improved blood pressure. Epidemiological (population) studies show a link between consumption of both black and green tea and reduced risk of cardiovascular disease, including heart attack and stroke.
Mood, Brain and Cognitive Function: I have always found that a cup of tea relaxes me, and it’s not surprising. Both green and black tea contain an amino acid called L-theanine, which increases the activity of the inhibitory neurotransmitter GABA and dopamine, which can induce a calming effect. The combination of L-theanine and caffeine in tea has a synergistic effect and has been noted to improve mental concentration, often referred to as “alert calmness”.
Studies support a beneficial impact of tea on mood, cognition (memory and attention) and brain function (working memory). Population studies indicate a protective effect against dementia and Alzheimer's disease.
Cancer: The flavonoid catechin EGCG in green tea has been associated with angiogenesis inhibition (lowering blood supply to tumours), altering cell signal pathways and promoting apoptosis (death of damaged cells). While there are certainly health benefits associated with the phytonutrients in tea, I would never consider tea or any supplements derived from tea to be a “magic bullet’ against cancer. And for the record: if anyone ever suggests that a single food or nutrient is a cure, then make sure you run very, very far in the opposite direction.
Bone health: studies show a link between tea consumption and bone density, but whether this flows through to lower fracture-risk is unclear.
Dental and oral health: tea consumption is associated with improved gum health and lower incidence of cavities, tooth loss and bad breath, likely due to tea's antibacterial effects and also its fluoride content (more on that in Part 2 next week!).
Weight loss: Studies indicate that green tea may have a modest weight-loss effect, possibly due to a slight fat-burning boost from the catechins and caffeine.
The Verdict?
Tea is one of the healthiest beverages you can choose, especially if you add in a squeeze of lemon and/or leave out sugary sweeteners! But it’s not a "magic bullet" cure-all. It won't magically erase the adverse impacts of a junk-laden diet or sedentary lifestyle.
After decades of reductionist thinking, the consensus in nutrition science is that it is the consistent pattern of our overall daily diet that makes the biggest difference to our health and longevity. And the epidemiological studies are very clear on that - tea is indeed a part (albeit only one part) of diets of people who live longer and enjoy better health.
So if you enjoy tea, it can certainly be one piece in your “healthy diet puzzle”.
There is a LOT more to tell you about tea! But if I put everything in one place this post would be way too long. So....
This post is Part 1 of a Two-Part Series. Check back next Wednesday when I share some things about tea you are probably not aware of, as well as my top tips for a healthier tea time!
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