Time for a cuppa...

School Of Nutrition Posted Dec 23, 2013 Future Fit Training


Tea is one of the most popular drinks in Britain. We drink 165 million cups every day. That’s 15 billion litres of tea every year! [1] Researchers claim not only that tea rehydrates as well as water does, but that it can also protect against heart disease and some cancers.

Time for a cuppa...

Here we examine some of the health benefits of a good cuppa and set the record straight on some of the myths associated with tea.

Tea comes from the leaves of the plant Camellia sinensis and includes black tea, green tea, white tea and oolong tea, the difference being in the way the leaves are processed. While the leaves for black tea are fully oxidised, those for green teas are lightly steamed before being dried. Oolong tea is made from partially oxidised leaves, but only young leaves that have undergone minimal oxidation are used to make white tea. Black tea represents approximately 72% of the total tea consumed in the world, whereas green tea accounts for approximately 26%. [2]

What is in your cup of tea?

Tea has no calories. Using semi-skimmed milk adds around 13 calories per cup, but you also benefit from the valuable mineral calcium, which is important for bone health. Tea is a good source of the minerals manganese - essential for bone growth and body development, potassium - vital for maintaining body fluid levels, and fluoride – needed for dental health. [1]

Tea contains catechins, a type of flavonoid. White and green teas have the highest concentration of these while oolong and black teas have less due to the oxidative preparation. Tea also contains caffeine, the amount of which may vary between 30- 90 mg/cup depending on the type of tea and method of brewing. Other medicinal ingredients in tea are theobromine and theophylline, both of which are found in smaller quantities. [3]

Potential health benefits of tea

Flavonoids are powerful anti-oxidants which have been shown to have a protective role against certain conditions such as heart disease, stroke and some cancers. [4]

Cardiovascular effects

While a significant number of studies have demonstrated that total tea or flavonoid consumption is linked to a decreased risk of heart disease and stroke, not all studies have shown similar protective effects. In an attempt to reach a conclusion regarding the effect of tea drinking on the risk of coronary heart disease (CHD), two meta-analyses were conducted using the results from all the available population studies. Using results from seven prospective cohort studies, Huxley [5] found that individuals in the top third of dietary flavonoid intake had a 20% lower risk from CHD mortality, compared to those in the bottom third. The conclusions from a second meta-analysis that included observational studies investigating the relationship between tea drinking and CHD suggested that drinking 3 cups of tea a day reduces the risk of myocardial infarction by 11%. [6] 

Anti-cancer effects

Although animal studies have provided evidence that the flavonoids found in tea may have cancer preventative effects, [4] the results of human studies—both epidemiologic and clinical studies—have been inconclusive. Recent studies show conflicting results with benefit for some cancers but not for others. For example, while green tea may reduce the risk of developing breast cancer, an effect which has been ascribed mostly to the flavonoids’ ability to modify the metabolism of oestrogens [7], it does not appear to reduce the risk of developing prostate cancer, and black tea may increase prostate cancer risk [8].

Also, a recent meta-analysis shows that the consumption of green tea appears to reduce oesophageal cancer but black tea does not [9]. Inconsistencies in study findings may be due to variability in tea preparation, tea consumption, the bioavailability of tea compounds (the amounts that can be absorbed by the body), lifestyle differences and individual genetic differences. [10]

Other effects

Due to the accumulating evidence that suggests oxidative stress plays a pivotal role in neurodegenerative diseases, the effect of the flavonoids in tea is now being considered as possible protective agents in progressive neurodegenerative disorders such as Parkinson's and Alzheimer's diseases.  Epidemiological studies have shown a reduced risk of Parkinson’s disease with the consumption of 2 or more cups of tea a day. [11] [12] There is also some evidence that the flavonoids in green tea may be protective against Alzheimer’s, although further studies are required. [13]

Myth busters...

Does drinking tea count towards your 8 glasses of fluid a day?

Tea contains approximately 99% water. Both the Food Standards Agency and the British Dietetic Association advise that tea can help towards meeting daily fluid requirements. Contrary to popular belief, the caffeine content of a cup of tea is not sufficient to cause a diuretic effect in the majority of individuals.

Does drinking tea result in iron deficiency?

Certain compounds in tea can reduce the absorption of non-haem iron from vegetable sources such as cereals, pulses and dried fruit, but drinking tea will not result in iron deficiency for healthy individuals who are consuming a varied and balanced diet. Nevertheless, it is advised that those who have a poor iron status or are at risk of iron deficiency should avoid drinking tea with meals, and should instead wait for an hour after the end of a meal before enjoying a cup of tea.

Conclusion

Tea contains flavonoid compounds, which are powerful antioxidants that may be relevant to heart disease and cancer prevention. So, as well as eating more fruit and vegetables, antioxidant intake can be topped up by drinking more tea, helping to promote overall health and well-being. Tea is also a natural source of fluoride and drinking 3-4 cups can make a significant contribution to your daily fluoride intake for good dental health. The milk in 4 cups of tea will provide around one fifth of your daily calcium requirements. And remember, if you are not at risk of iron deficiency, you can enjoy a cuppa at any time of the day!

Written by Victoria Trowse

 

    

REFERENCES

1. UK Tea Council – accessed online at http://www.tea.co.uk/

2. Katiyar, S.K. et al (1996). Tea in chemoprevention of cancer: epidemiological and experimental studies. Int J Oncol 8: 221-238.

3. Schwalfenberg, G., Genuis, S.J. and  Rodushkin, I. (2013). The benefits and risks of consuming brewed tea: beware of toxic element contamination. Journal of Toxicology 2013: Article ID 370460, 8 pages.

4. McKay, D.L. and Blumberg, J.B. (2002). The Role of Tea in Human Health: An Update. JACN 21: 1-13.

5. Huxley, R.R. and Neil, H.A. (2003). The relation between dietary flavonol intake and coronary heart disease mortality: a meta-analysis of prospective cohort studies. Eur J Clin Nutr, 57: 904-8.

6. Peters, U., Poole, C. and Arab, L. (2001). Does tea affect cardiovascular disease? A meta -analysis. Am J Epidemiol, 154: 495-503.

7. Fuhrman, B.J. et al (2013. “Green tea intake is associated with urinary estrogen profiles in Japanese-American women,” Nutrition Journal 12: 25.

8. Montague, J.A. et al (2012).“Green and black tea intake in relation to prostate cancer risk among Singapore Chinese,” Cancer Causes Control 23: 1635–1641.

9. Zheng, J.S. et al (2013). “Effects of green tea, black tea, and coffee consumption on the risk of esophageal cancer: a systematic review and meta-analysis of observational studies,” Nutrition and Cancer, 65 (1): 1–16.

10. National Cancer Institute – accessed only at http://www.cancer.gov/cancertopics/factsheet/prevention/tea

11. Checkoway, H. et al (2002). Parkinson's disease risks associated with cigarette smoking, alcohol consumption, and caffeine intake. Am J Epidemiol 155: 732–738.

12. Tan, E.K. et al (2003). Dose-dependent protective effect of coffee, tea, and smoking in Parkinson's disease: a study in ethnic Chinese. J Neurol Sci 216: 163–167.

13. Davinelli, S. et al (2012). Pleiotropic protective effects of phytochemicals in Alzheimer's disease. Oxidative Medicine and Cellular Longevity, 2012: Article ID 386527, 11 pages.

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