Fancy a cuppa?

Potable tea as a water infusion of young leaves from the tea tree (botanical name Camellia sinensis) is one of nature’s health beverages.

Its multi-molecular chemical composition provides a recreational drink with a variety of beneficial effects. Besides nourishing the body, tea may act as a benign cardiovascular and neural stimulant, a coolant, or cariostatic mouthwash. Consequently, tea is very popular – apart from water, it is the most widely consumed liquid beverage worldwide.[1]

Natural tea (infusions of the leaves of Camellia sinensis) contains cations, trace elements and organic molecules which impart its aroma, flavour and color. Added substances like bergamot oil in Earl Grey may modify the characteristics – these chemicals also have physiological effects on mammalian cells and metabolism.

Health claims have been made surrounding tea drinking for many years; some of them beneficial, others confusing. For example, a contemporary Korean chocolate manufacturer includes tea extract in its product and claims a wide range of benefits deriving from its efficacy, from restraining cancer, ageing and allergies to lowering blood cholesterol, blood pressure and tooth decay.

This article reviews some of these assertions, and attempts to clarify the situation with recent research findings, many of which offer revealing scientific evidence about their validity and impact on living.

These health claims seem to devolve into four main functional areas: A; Tea contents and provision of nutrients. B; Physiological – organoleptic, neural and metabolic effects. C; Health – ensuring continued health, maintaining, promoting or restoring wellbeing and preventing disease. D; Dental health.

A: Tea contents and nutrients

Tea is a complex mixture of chemicals in solution, rendering a uniquely flavoured and colored brew. It contains many nutritional trace elements[2] and many organic compounds3, most of which may play a roll in metabolism. Sodium, potassium, magnesium, calcium as cations, fluoride, aluminium, manganese, copper iron and zinc as trace elements are found in dilute amounts in tea infusions[2,4,5]. All these molecules contribute to the overall nutritional intake for tea drinkers.

Tea effusions contain many other organic molecules as soluble solids. Some of the most prevalent are theaflavins, polyphenols, flavonoids (like quercetin and apigenin), caffeine, gallic acid and catechins, all of which are in potable tea, after preparation with water for imbibing.[3]

Three major kinds of tea are imbibed: black (78%), green (20%) and oolong (2%). Green tea contains many polyphenols (the cathechins) including epigallocatehechin and epigallocatehechin-3 gallate. In a fermentative process, cut and partially dried tea leaves are subjected to controlled enzymatic biotransformations at slightly elevated temperature that transforms tea leaves to black tea which yields characteristic flavour and color when brewed with water. The cathechins are the main polyphenolic flavonols that undergo major transformation to form theaflavins and thearubigins that are prevalent in potable black tea.[4,5]

B: Physiological effects

• Organoleptic properties.

The aroma and flavours of tea depend on the existence of many organic substances, most of which occur in trace amounts in tea. The characteristic aroma of most teas derive from phenyl-ethyl alcohol, citronellol, hexenol, beta-phenyl acetic aldehyde, terpenes, terpene alcohols, lactones, ketones, esters, spiro compounds, monoterpines and 2-phenyl-2-butenal, all of which may co-exist in varying proportions in tea brews.[6,7] Some specific molecules can pleasantly dominate the tea fragrance, such as theaflavin.[7,8]

Earl Grey tea is composed of black tea with added essence of bergamot oil, an extract from the rind of bergamot orange, which has a pleasant, refreshing scent. Bergamot oil itself contains bergapten, bergomottin and citropten, which can be found in grapefruit juice, celery, parsnips, and Seville orange juice.[9]

Excess imbibed bergamot oil in Earl Grey may be toxic.[10] Repeating muscle cramps, fasciculations, limb parasthesias and reduced visual acuity are among toxic symptoms from drinking excessively strong Earl Grey tea. These reversible symptoms are due to alkoxypsoralens, (a group of nonpeptide K+ blockers acting on voltage gated ion channels in Renvier nodes) in the bergamot oil, and not from Camelia sinensis tea.[9,10] Hyperexcitability may be enhanced by prolonged opening of voltage-gated sodium channels due to bergapten.[10]

• Mental effects.

The benign neural and cerebral stimulatory effect of caffeine is well known, recorded and used in many drugs. For example, caffeine, in doses of 100mg per tablet, is safely used in combination with many other drugs to modulate their restraining effects on the central and autonomic nervous systems. Drugs like opiates (e.g. codeine), ergotamine, barbiturates and acetaminophen drugs are all available in combination with caffeine.[11] Tea contains about 100mg/dL of caffeine, an amount frequently exceeded by most, especially as many people drink more than one (250 mLs) cup of tea at one sitting.[3]

The caffeine in tea not only acts as a nervous system stimulant, but also inhibits platelet aggregation by upregulating human platelet adenosine A2A receptors.[12] Since blood platelets are the major mediators of blood coagulation, this biological phenomenon inhibits blood-clot formation.[12] For this reason, claims have been made for tea improving long-term beneficial effects on cardiovascular disease.

• Metabolic effects.

There is a lot of data to support the notion that dietary intake of flavonoids from tea and other sources (e.g. onions, apples, red wine, and broccoli) is associated with reduced cardiovascular disease risk.[13,14,15,16] Flavanols are important if tea (or red wine) is regularly consumed, as tea drinkers have better blood lipid profiles with reduced LDL levels.[17,18]

C: Health and survival

Drinking tea to prevent cancer seems to be feasible.[4] Tea may have a slight modulating effect on growing cancer cells, but overall it does not stop cancerous cell growth, nor cure it.[19,20]

Green tea catechins and epigallocatechin gallate both have anti-thrombotic activity; this is important as coronary vascular thrombosis is the mechanism underlying classical myocardial infarctions that has high mortality and morbidity rates worldwide, particularly in the USA and Canada.[21,22]

Regular dietary intake of tea flavonoids reduces the risk of coronary heart disease, incidence of stroke and, consequently, mortality.[13,16] This is achieved, in part, through successful reduction of blood cholesterol and reduction of blood pressure by regular daily tea drinking.[23,24]

Flavonoids and phenolic compounds in tea have strong anti-oxidant properties, and act as scavengers for superoxide anions.[24,25] Total flavonol intake can be increased consumption of red wine, cocoa, chocolate or grape juice, but not orange juice or grapefruit juice.[25, 26, 27,28]

The effect of tea flavonoids on platelet reduction is unlikely to fully explain the risk of cardiovascular events noted in epidemiological studies,[29] but rather black tea consumption seems to reverse endothelial dysfunction, which is one of the major contributors to atheroma formation.[4]

D: Dental effects

• Decay and fluoride.

Epidemiological data suggests increased tea consumption decreases the prevalence of tooth decay.30,31 Tea contains various amount of fluoride ion (2-7 ppm/L or mgm/L),2,31 and the reduction in decay has been attributed to the increased fluoride intake by tea drinking.[32,33]

It is a well-established fact that 1ppm/L of fluoride in the drinking water reduces tooth decay in humans.[34,35] There are many other organic and inorganic molecules in tea,[2,3,31,36] and many of these may modulate the effect of fluoride on tooth decay.[37] Experimentally high fluoride drinking water concentrations (20 ppm/L) virtually shuts down tooth decay formation.[38] With in vivo animal research, tea infusions also show marked reductions of tooth decay formation, and yellow tooth discoloration, but not nearly as much as high fluorides in the drinking water.[38,39]

• Staining.

Tea and coffee are universally, but falsely, blamed for most tooth staining. Acquired discoloration of teeth may also be due to extrinsic stains from other dietary substances like habitual betel nut or tobacco chewing. Diffusion of pigments into dental tissues after formation may partially derive from extrinsic stains in tea and coffee, but also from necrotic pulps and endodontic materials.

Some pigments are incorporated during formation of dental tissues such as bile pigments, prophyrins and tetracyclines.[40] The commonest form of removing extrinsic dental tea stains is through tooth brushing at home, or by regular professional check-ups which usually include using light prophylaxis abrasive polishing paste. There are numerous ‘at-home’ and ‘professional in-office’ bleaching products to successfully whiten stained teeth. The active bleaching agents are either hydrogen peroxide or carbamide peroxide, each varying in concentration and methods of application.[41]

Experimentally black tea does not induce dental frangibles (attrition, abrasion or erosion) through tooth softening nearly as much as fruit juices or soft drinks do.[43,44] Black tea alone does not induce tooth softening, nor initiates decalcification even if drunk frequently in large amounts.[38,39,43]

Dentinal sensitivity and Fruit-flavored Tea: Fruit acids and flavours are added to teas.[42] These fruit flavoured teas all induce erosion in enamel and remove the smear layer from dentine, with the potential for dentinal hypersensitivity reactions. Most fruit-flavoured teas contain pieces of fruit such as guava, pear, mandarin, lemon, liquorice, mango, lychee, black currants, a variety of acid- bearing berries (strawberry, raspberry, loganberry, elderberry etc) and Hibiscus.[45] All these additives, including Vitamin C as ascorbic acid, enhance the organoleptic properties of the tea, but contribute to the acidification of the potable tea and its potential for inducing frangibles with excess imbibing.[42]


Regular tea drinking has mild neuro-stimulatory effects from its caffeine content. When imbibed frequently tea has a benign, beneficial long-term effect on the circulation vasculature, the heart, and longevity is increased due to reduced morbidity from heart disease. Besides increasing the feeling of well-being, tea is also cariostatic, but can cause minor staining of teeth.


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