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The Health Effects of Tea

Updated: Nov 20, 2023

Tea is the lifeblood of every Irish household. But is this soothing indulgence a good thing for your health? Read on as we spill the tea…


Introduction

Us Irish love our tea. In fact, the average Irish person supposedly drinks 1,460 cups of tea per year. That’s 4 cups per day (!) which, upon hearing it sounds excessive, but upon reflection, seems spot on. Considering this is a huge part of our everyday lives, wouldn’t it be prudent to have a look at what the scientific literature has to say about its health effects? I think it would, so let’s get to it.


Lyons tea vs. Barry's tea

The age-old battle between Lyons and Barry’s Tea. Source: The Daily Edge


Why Tea Might Be Healthy

All types of tea contain a variety of polyphenols—or plant chemicals—that can act as antioxidants. This means that they can neutralise (or switch 'off') the damaging effects of certain unstable molecules (known as free radicals) produced by the body, which is the main mechanism underpinning the purported health benefits of tea. The main polyphenols in green tea are called catechins, but other polyphenols in tea include flavonols, phenolic acids, and others (1). The evidence for health benefits from flavonols, in particular, has been mounting. Specifically, flavonols may reduce blood pressure, low-density lipoprotein (LDL) cholesterol, and markers of diabetes risk (2). As such, guidelines from a recent Expert Panel recommended a flavonol intake of 400–600 milligrams (mg) per day for the general population—for reference, a 240 millilitre (mL) cup of green tea contains ~320 mg of flavonols, and a 240 mL cup of black tea contains ~280 mg of flavonols (2).


Health Benefits of Tea

Because there has been a lot of research on the potential health effects of tea consumption, there have been two recent umbrella reviews—which are essentially reviews of reviews—that synthesised all of this evidence. In brief, tea consumption is consistently associated with a reduced risk of death, cardiovascular disease, type 2 diabetes, and a number of different cancers (3,4). In addition, some studies found evidence for a reduced risk of osteoporosis, cognitive disorders, and Parkinson’s disease for greater tea consumption, although the evidence for osteoporosis was rated as of low quality (3). Interestingly, the optimal dose for health benefits seemed to be at about 2–3 cups per day for risk of death, which is similar to the results for coffee and risk of death (3).


Different types of tea.

Source: Kitchen Zap


Health Risks of Tea

You’ll be glad to hear that the health benefits of consuming tea far outweigh any potential negatives. But, tea consumption has been associated with an increased risk of oesophageal cancer, i.e., cancer of the muscular tube that connects our mouth to our stomach, as well as gastric (stomach) cancer (3,5). Why is this the case, when tea seems to be protective against other cancers? Well, it’s likely not the tea, but the hot temperature of tea that causes inflammation to the oesophagus and stomach and increases the risk of this cancer. In fact, in studies where researchers adjusted for the temperature of tea, tea consumption was associated with a reduced risk of oesophageal cancer (6). What this means is that if you enjoy a good cuppa, it’s probably best to not drink it too hot (i.e., >55–60°C) (3).


Hot tea.

Allow your tea to cool a bit before drinking. Source: Orissa Post


Which is the Healthiest Type?

Both of the main types of tea, i.e., green tea and black tea, are associated with health benefits. However, there are some differences in their bioactive constituents. One cup of green tea contains about 30–42% catechins—a form of polyphenol, whereas one cup of black tea contains about 10–12% catechins (1). However, black tea contains more flavonoids, which as we discussed earlier, are associated with health benefits. From my point of view, the practical takeaway is to drink whichever you prefer.


Summary

To wrap things up, here are the main takeaways:

  • Tea is rich in polyphenols which act as antioxidants

  • Tea is associated with a myriad of health benefits, with an optimal dosage for certain outcomes considered at about 2–3 cups per day

  • Tea (when drank hot) is associated with an increased risk of oesophageal cancer

  • Both green tea and black tea offer health benefits


So, for Afternoon Tea Week, why not celebrate this weekend by heading out and enjoying some tea and cakes somewhere nice? Or at the very least, when your Mam says ‘I’ll put the kettle on’, take solace in knowing that this simple habit is likely good for your health.


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Thanks for reading and have a lovely weekend!


Patrick Elliott, BSc, MPH

Health and Nutrition Science Communication Officer at Training121


Health Disclaimer: this article is for informational and educational purposes only, and is not a substitute for professional advice. For health advice, speak to a physician or other qualified health-care professional, and for nutrition advice, speak to a qualified nutrition professional (e.g., registered dietitian). The use of information on this site is solely at your own risk.


References

(1) Khan N, Mukhtar H. Tea polyphenols for health promotion. Life Sci. 2007;81(7):519–33. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3220617/


(2) Crowe-White KM, Evans LW, Kuhnle GGC, et al. Flavan-3-ols and Cardiometabolic Health: First Ever Dietary Bioactive Guideline. Adv Nutr. 2022;13(6):2070–83. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9776652/


(3) Yi M, Wu X, Zhuang W, et al. Tea Consumption and Health Outcomes: Umbrella Review of Meta-Analyses of Observational Studies in Humans. Mol Nutr Food Res. 2019;63(16):e1900389. Available at: https://onlinelibrary.wiley.com/doi/10.1002/mnfr.201900389


(4) Kim TL, Jeong GH, Yang JW, et al. Tea Consumption and Risk of Cancer: An Umbrella Review and Meta-Analysis of Observational Studies. Adv Nutr. 2020;11(6):1437–52. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7666907/


(5) Sheikh M, Poustchi H, Pourshams A, et al. Individual and Combined Effects of Environmental Risk Factors for Esophageal Cancer Based on Results From the Golestan Cohort Study. Gastroenterology. 2019;156(5):1416–27. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7507680/


(6) Zheng JS, Yang J, Fu YQ, Huang T, Huang YJ, Li D. Effects of green tea, black tea, and coffee consumption on the risk of esophageal cancer: a systematic review and meta-analysis of observational studies. Nutr Cancer. 2013;65(1):1–16. Available at: https://www.tandfonline.com/doi/full/10.1080/01635581.2013.741762


Technical Terms

Polyphenols: These are a group of phytochemicals—or plant nutrients—that act as antioxidants and improve our health. Health benefits from polyphenol intake include reductions in LDL cholesterol, improved cognition, and other metabolic improvements.


Antioxidants: These are chemicals that are found in a range of foods (particularly plant foods) that play protective roles in the body. This includes neutralising the effect of free radicals and reducing oxidative stress, which is thought to be part of the reason why antioxidants from foods like fruits and vegetables are associated with a reduced risk for a range of chronic diseases. In addition, our body makes our own antioxidants (e.g., glutathione peroxidase) which are important components of our immune system. It is important to note that while antioxidants in foods seem to be protective against disease, antioxidant supplements are not, and may be harmful.


Free radicals: These are unstable molecules that can damage cells in our body. They are unstable because they do not have a full set of electrons and therefore seek electrons from other molecules, damaging them in the process. Free radicals are an inevitable part of human metabolism, which is all the more reason to eat a diet high in antioxidant-rich foods so that these free radicals can be switched ‘off’ when needs be.


Umbrella review: These are a type of review that reviews evidence from other reviews, typically systematic reviews (with or without meta-analysis). As more evidence on certain topics is published, umbrella reviews become a necessity to summarise a broad evidence base.

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