Tea – Composition and Health Implications


Tea arrived in Europe in the 18th century, having been drunk elsewhere for centuries, for example by the Chinese for probably 5000 years. Tea was initially sold in coffee houses but became more popular than coffee, perhaps because of early Royal patronage, and by the 1750’s tea houses and tea gardens were common in and around London. The popularity of tea was such that from the latter part of the 18th to the beginning of the 19th century a transition took place in the drink of the laboring class as tea replaced beer and gin.

5 different teas

Composition of teas


Tea leaves contain, in quantities equivalent to 20–30% of the dry weight, a range of polyphenols, particularly the flavan-3-ols, namely (+)-catechin and (–)-epicatechin and their gallate derivatives.

green tea

Green Tea

The types and proportion of flavan-3-ols in the tea leaf varies with season, the age of the leaf, climate, and horticultural practices. In addition, major changes occur during processing. In the rolling and crushing used to manufacture oolong and black tea, polyphenol oxidase released from the leaf endoplasmic reticulum catalyses the condensation of the catechins to the yellow–orange colored theaflavins. These undergo oxidation and randomly polymerise to form high molecular weight thearubigins, which are major components and impart the red–brown color that characterizes black tea. These compounds are responsible not only for the colour of black tea but also for its astringent flavour. In comparison with green tea, black tea is low in monomeric catechins but high in oligomeric derivatives, most notably thearubigins (Haslam, 1998). Fermentation, however, does not affect the level or composition of flavonol glycosides, which are similar in black and green tea.

The polyphenols in tea can react with divalent ions such as iron. This could reduce the bioavailability of iron but this effect is not definitively associated with any increased morbidity. The presence of catechins indicates that tea extracts have considerable antioxidant activity. In certain model systems, such antioxidant activity compares favourably with the antioxidant nutrient vitamin E.

Other components

oolong tea

Oolong tea

Consumption of tea probably provides a negligible intake of macronutrients. For example, less than 2% of the hot-water-soluble solids of black tea are proteins, 4–5% are carbohydrates and 2–3% are lipids, mainly linoleic and linolenic acids. However, macronutrient content is markedly increased by the UK habit of adding milk and sugar.

Tea also contains a range of micronutrients including manganese, potassium, niacin, riboflavin, folate and zinc. However, the contribution of tea to the overall vitamin and mineral intake in the UK has declined in recent years. According to MAFF’s National Food Survey statistics, tea consumption has decreased by more than 50% in the last 20 years to about 3.5 cups per person per  day  (one  cup  in  the  UK is typically 200 mL). In addition, the tea drunk today may be less rich in micronutrients than in previous decades as infusion times have decreased from 5–6 min to 40–60 s.

All types of tea also contain significant quantities of the purine alkaloid caffeine together with smaller amounts of theobromine. About 80% of the purine alkaloids are extracted into the water-soluble phase during brewing. Typically, a 200 mL cup of black tea contains 50–100 mg of caffeine.

Health implications of tea

There are suggestions that tea and tea catechins may have a variety of health effects in man. Most interest has been focused on the possibility that tea may inhibit the development of heart disease and cancers, diseases that account for the majority of premature mortality in developed countries.


Tea and heart disease

A number of epidemiological studies have suggested that consumption of tea per se or diets rich in the polyphenols found in tea are associated with decreased risk of heart disease and associated conditions. A prospective study in the Netherlands (Geleijnse  et al., 1999) of 3454 men and women aged 55 years found a significant inverse association between tea intake and radiographically quantified aortic atherosclerosis. In addition, green tea consumption appears to be associated with about a 30% decrease in aortic lesion formation in hyper-cholesterolaemic rabbits (Tijburg et al., 1997).

A recent meta-analysis of 10 cohort and seven case-control studies serves to emphasize the hetrogeneity in reported effects. The authors estimated an 11% decrease in the rate of myocardial infarction with an increase in tea consumption of around three cups a day. However, the possibility of publication bias and evidence of geographical differences (a decreased risk was consistently found in continental Europe but studies in the USA and UK showed little or no effect, or even an increased risk of CHD) urges caution in the interpretation of this finding (Peters et al., 2001). Another Dutch study (Arts et al., 2001a) used data from the Zutphen Elderly Study (a prospective cohort of 806 men aged 65–84 years at baseline) to assess whether total catechin intake, which was 72 ± 47.8 mg/day at baseline, mainly from tea, apples and chocolate, influenced the risk of death from ischaemic heart disease or incidence  or  death  from  stroke. They report that catechins, whether from tea or other sources, may reduce the risk of ischaemic heart disease death but not stroke.

heart diseaseOne possible mechanism by which tea may reduce heart disease risk is via the ability of catechins to prevent the oxidation of  low-density lipoprotein cholesterol to an atherogenic form. In vitro, the oxidation of low-density lipoprotein by endothelial cells, macrophages and Cu2+ can be inhibited by a wide range of polyphenols and polyphenol-rich extracts (Duthie et al., 2000). Such effects may be due to the direct scavenging by the polyphenols of the oxidising species or may result from the polyphenol-mediated regeneration of vitamin E in the low-density lipoprotein. However, whether such in vitro antioxidant effects also occur in vivo and translate into reducing the risk of developing heart disease is unclear at present. The consumption of tea may also prevent atherosclerosis by mechanisms that do not necessarily involve the antioxidant properties of catechins  (Duthie  et  al., 2000). For example, in vitro studies suggest that tea extracts may prevent platelet adhesion and aggregation by inhibiting the cyclooxygenase pathway and reducing the cyclic 3′,5′-adenosine monophosphate (AMP) response of platelets to prostaglandin I2.

Moreover,  reported  vasodilatory  effects  of   tea extracts and polyphenols may be due to their affecting enhanced nitric oxide generation, cyclic 3′,5′-guanosine monophosphate (GMP) accumulation and other endothelium-dependent relaxation factors. The relevance of these findings to normal human diets still needs to be established. Caffeine in tea may reduce blood coagulation by inhibiting thrombin-stimulated thromboxane for- mation. It has also been suggested that reported hypocholesterolaemic effects may reflect reduced cholesterol absorption from the intestine, caused by flavan-3-ol esters reducing the solubility of cholesterol in mixed micelles.

Tea and cancer

cancerEpidemiological studies of black tea consumption and cancer have produced mixed results. For green tea consumption, a review published in 1998 found that out of five studies on the incidence of colon cancer, three found an inverse association, one reported a positive association and one found no statistically significant association. For rectal cancer, of four studies one reported an inverse association and two reported an increased risk (Bushman, 1998). The inconclusive findings of these and other studies may reflect problems of measurement error (recall bias in case-control studies) and specificity of exposure (duration and amount not specified), or lack of control of potentially important cofounders. At the present time the epidemiological evidence is at best inconclusive as to whether there is any benefit from either black or green tea. In contrast to human epidemiological studies, many in vitro and animal studies have demonstrated the inhibition of chemically induced cancer by tea and tea polyphenols. For example, rats fed a diet containing 1% green tea catechins have a significantly reduced mortality from mammary tumors following treatment with a chemical carcinogen compared with rats given the carcinogen alone (Hirose et al., 1994). Hamsters fed green tea polyphenols display fewer hyperplastic pancreatic duct lesions after treatment with N– nitrosobis(2-oxopropyl)amine (Majima et al., 1998). In a comprehensive study, Yang et al. describe the ability of both green and black tea infusions to inhibit N-nitrosodiethylamine-induced lung carcinogenesis in knockout mice (Yang et al., 1998). Tea extract also significantly reduced the progression of chemically induced, non-malignant adenomas to malignant adenocarcinomas. Furthermore, the spontaneous formation of lung tumors and rhabdosarcomas was inhibited 50% in rats fed either black or green tea infusions.

There are a number of mechanisms by which tea may potentially influence both carcinogenic initiation and promotion (Duthie  et  al.,  2000).  In brief, these include direct and indirect antioxidant protection of DNA, the modulation of enzyme systems such as cytochrome P450 complexes that metabolise carcinogens or pro- carcinogens to genotoxins and the modulation of malignant transformation, apoptosis and gene expression. Gut flora profiles could also be altered to decrease the formation  of potentially carcinogenic compounds such as ammonia and amines.

Bioavailability of tea catechins

Consumption of a single dose of green tea extract results in a small but significant increase in plasma concentrations of total catechins. The effect is less for black tea arguably because of the potentially poor absorption of high molecular weight thearubigens and theaflavins, which predominate in black tea. The presence of milk does not appear to affect the absorption of catechins from tea (van het Hof et al., 1999). In addition, radiolabelling studies with primates suggest that significant quantities of (–)-epigallocatechin gallate or its metabolites can be found in tissues indicating that they may arrive at target sites within cells in peripheral tissues (Suganuma et al., 1998). This is an essential requirement if consumption of the catechins found in tea is to exert effects similar  to that observed in cell culture.


In many biological systems, extracts of tea have  a wide range of effects with potential health benefits. In cell culture and animal models they may inhibit oxidation of low density lipoproteins, prevent mutations and be anti-carcinogens. Much of this activity is ascribed to the polyphenolic components of tea, in particular the catechin-derivatives. More studies are required to establish the bioavailability of these compounds and their effects in vivo before any health benefits can be established with certainty. The impact of these compounds when consumed as part of a normal diet and in amounts normally consumed by humans is not yet clear.

24 Responses

  1. Jacquetta says:

    Your site can go viral, easily.

    • Dieticle Team says:

      Thank you for your comment, Jacquetta.

      We’re doing our best. You can help us by sharing this post with your friends.

  2. Kala says:

    I see you don’t monetize your site, i think there is one
    opportunity to earn extra money on your page, search in google for adsense.

  3. Jocelyn says:

    Great blog! It could go viral with some promotion.

  4. Matee says:

    At last! Someone with real expertise gives us the answer. Thanks!

    • Dieticle Team says:

      You’re welcome Matee! Our articles are mainly submitted anonymously, but they’re checked by professionals and then published.

  5. Ana says:

    I’m not that much into science and stuff, but I like this post… Continue with a good job, Dieticle!


  6. birmingham girl says:

    I love tea, but I never knew that there’s this much to be written about it.

  7. amanda says:

    I choose to write a research paper on Tea on my chemistry subject, and this is exactly what I’m going to write. I hope it won’t be a problem for you to copy some of this content? I’ll mention Dieticle in the reference section, no worries.

  8. anna az says:

    I didn’t know that tea has this much impact to our health. I was thinking like it’s like coffee.

  9. Anonymous says:

    Hello There. I found your blog using msn. This is a very well written article.
    I will make sure to bookmark it and return to read more of
    your useful information. Thanks for the post. I’ll definitely comeback.

  10. Anonymous says:

    I love this site – its so usefull and helpfull

  11. Anonymous says:

    You’ve gotten great knowlwdge on this website

  12. Anonymous says:

    I just want to say I am just new to blogging and honestly enjoyed you’re web site. Very likely I’m want to bookmark your site . You actually have excellent articles and reviews. Many thanks for sharing with us your web-site.

  13. Anonymous says:

    Simply want to say your article is as astonishing.
    The clearness on your post is simply excellent and that i could suppose you are knowledgeable in this
    subject. Fine along with your permission let me to grab your feed to stay
    updated with imminent post. Thanks a million and please carry
    on the rewarding work.

  14. Anonymous says:

    Very neat blog.Really looking forward to read more. Cool.

  15. tu says:

    Your blog has the same post as another author but i like your better.;~,*.

  16. hey there and thank you for your info – I’ve certainly picked up something new from right here. I did however expertise some technical issues using this site, since I experienced to reload the website many times previous to I could get it to load correctly. I had been wondering if your web host is OK? Not that I’m complaining, but slow loading instances times will sometimes affect your placement in google and could damage your quality score if ads and marketing with Adwords. Anyway I’m adding this RSS to my email and could look out for a lot more of your respective fascinating content. Ensure that you update this again very soon..

    • Sean says:

      Thanks for letting me know Corburt. I have been trying to resolve the technical issues to improve the site speed and user experience!

  17. Anonymous says:

    Can I say that it is a relief to discover someone that really knows what they’re talking about on the internet? I cant believe you’re less well-known since you definitely have a gift.

  18. Anonymous says:

    My brother recommended I might like this web site. He was entirely right. This post actually made my day. You cann at imagine simply how much time I had spent for this info! Thanks!

  19. Korona says:

    I’m not that much of a online reader to be honest but your
    sites really nice, keep it up! I’ll go ahead and bookmark your website
    to come back in the future. Cheers

  20. Anonymous says:

    Thanks for all of your effort on this web page. Kim enjoys participating in research and it’s really easy to understand why. My partner and i hear all about the lively means you create simple tips and hints via the website and therefore welcome participation from some others on this concept so my daughter is actually being taught so much. Enjoy the remaining portion of the year. You’re doing a very good job.

Leave a Reply

Your email address will not be published. Required fields are marked *