A Skeptical (and Scientific) Look at the Alleged Health Benefits of Tea

How many of the alleged health benefits of tea are real, and how many are just snake oil?
How many of the alleged health benefits of tea are real, and how many are just snake oil?

I should start by saying any questions you had before reading this may not feel resolved and even might multiply by the end of this article (if you so honour me with your time and attention). My inner skeptic is still unsatisfied; really, he’s never satisfied so it’s not something I’m too alarmed at.

“Too Long; Didn’t Read” version: the health claims about tea are a story of vagueness encapsulated by very good-looking marketing. Many of the pages have yet to be written. All told though, you are still unlikely to go wrong with a ‘cuppa’ of your favorite Camellia Sinensis leaves.

Apart from the effects of caffeine, I could not find any information on the detriments of tea (well, that and potential skin or tongue burns).  Again, skeptic became skeptical.

However, the main claims about tea’s health effects concentrate on anti-oxidant/cancer-fighting effects, reducing risk of heart attack/stroke, and weight loss. Other effects have been noted but I believe review of these areas will give you a good idea of what the other evidence will look like.

Take that, cancer! – Tea for Fighting Cancer?

Oxidation is nasty; it’s what causes rust on iron, makes apples turn brown, and it is what creates “free radicals” to float around in your body; these sometimes become mischievous and start messing with the cells they come into contact with. Anti-oxidants “deactivate” these yet not all are created equal, some can become “oxidizers” in certain conditions 5.

Different sources have shown anti-oxidant levels in tea. To put this in perspective, blueberries have 3.67, 70% dark chocolate has 11.91, and coffee has 2.5 mmol/100g. On the same scale, tea of varying types averages to about 3.33 mmol/100g 6.

When you hear about the anti-cancer aspects of tea, especially green tea, you are probably being referred to the polyphenol, theaflavins, and thearubigins 10, the second two found in black tea. These polyphenols have been shown to mess up cancer cells and their method of spreading 39,131415.

All that said, you also get anti-oxidants from what you eat and your body produces them itself 10. Vitamin C and E are amongst the most well-known of these substances. So while tea will give you a good source of anti-oxidants, the larger question of whether it is any better than other sources remains to be known.

Doing Your Heart Some Good – Tea and Heart Health?

There are some short-term studies on tea with improved “vascular reactivity”, meaning better blood pressure, in addition to black/green tea reducing Low Density Lipoprotein cholesterol4, the one that gets stuck on the sides of our arteries.

The downside to the data on tea and heart health is the type and length of most studies. A lot of information on this is correlational data: people who drink more black/green tea have lower incidence of heart attack/stroke 12 but that doesn’t mean one causes the other. Another issue is heart disease isn’t easily studied in the short-term; there haven’t been enough long-term studies to show conclusive effects of tea on cardiovascular health 6.

Sipping Off the Pounds – Tea for Weight Loss?

You will hear from numerous sources that tea helps with weight loss; hence the green tea supplements you find in natural food stores and pharmacies. What’s actually behind this, though? Well it looks like there may or may not be something to it, again specifically to do with green tea.

In one study, green tea “alleviated body weight gain and insulin resistance in diabetic and high-fat mice” 11. Yet a review of the data in 2012 7 from multiple randomized control trials (at least 12 weeks duration) with comparisons to control groups showed clinically non-significant weight loss in obese or overweight people. Another in 2014 1 found similar results.

This is not to discourage you from drinking tea for weight loss as the results of these and more studies do not state tea will cause you to gain weight. I’m sure any nutritionist would agree switching from high-sugar beverages to tea will inevitably lower one’s weight and improve health.

Conclusions

As you can see, there is some evidence for health benefits with tea, at least some teas.  There are a lot of articles you can read about the subject, some of which state simply the benefits of tea without citing where that information comes from. In my research I had to look carefully for those articles which provided a balanced perspective and linked to original empirical data (which itself can have bias depending on the testing criteria).


What I will encourage you to consider is your own experience: what does tea do for you in your day/life? Might you be getting benefits from the caffeine in tea or may you be having too much caffeine? What do you enjoy about making and drinking tea for yourself? “Health” means a lot more than the sum of my physiology and there may be many ways tea is improving your quality of life.

Continue reading:

References

  1. Baladia, E., Basulto, J., Manera, M., Martinez, R., & Calbet, D. (2013). Effect of green tea or green tea extract consumption on body weight and body composition; systematic review and meta-analysis. Nutricion hospitalaria, 29(3), 479-490.
  2. Carlsen, M. H., Halvorsen, B. L., Holte, K., Bøhn, S. K., Dragland, S., Sampson, L., & Barikmo, I. (2010). The total antioxidant content of more than 3100 foods, beverages, spices, herbs and supplements used worldwide.Nutrition journal,9(1), 1.
  3. Elmets CA, Singh D, Tubesing K, et al. (2001) Cutaneous photoprotection from ultraviolet injury by green tea polyphenols.Journal of the American Academy of Dermatology44(3):425–432. [PubMed Abstract]
  4. Fujita, H., & Yamagami, T. (2008). Antihypercholesterolemic effect of Chinese black tea extract in human subjects with borderline hypercholesterolemia. Nutrition research, 28(7), 450-456.
  5. Harvard School of Public Health.Antioxidants: Beyond the Hype.http://www.hsph.harvard.edu/nutritionsource/antioxidants/
  6. Helm, Laura, Macdonald Ian A. (2015) Impact of beverage intake on metabolic and cardiovascular health. Nutrition Reviews. Vol. 73 (52). P. 120-129 (http://nutritionreviews.oxfordjournals.org/content/nutritionreviews/73/suppl_2/120.full.pdf)
  7. Jurgens T.M., Whelan, A.M., Killian L., Ducette, S., Kirk S., & Foy E. (2012) Green tea for weight loss and weight maintenance in overweight or obese adults. Cochrane Database Systemic Review Dec 12; 12. DOI: 10.1002/14651858.CD008650.pub2
  8. Kristel Diepvens, Klaas R. Westerterp, Margriet S. Westerterp-Plantenga. (2007) Obesity and thermogenesis related to the consumption of caffeine, ephedrine, capsaicin, and green tea American Journal of Physiology – Regulatory, Integrative and Comparative Physiology Jan 2007, 292 (1) R77-R85; DOI:10.1152/ajpregu.00832.2005
  9. Lambert JD, Yang CS. (2003) Mechanisms of cancer prevention by tea constituents.Journal of Nutrition2003; 133(10):3262S–3267S [PubMed Abstract]
  10. National Cancer Institute. (2010) Tea and Cancer Prevention.http://www.cancer.gov/about-cancer/causes-prevention/risk/diet/tea-fact-sheet
  11. Park, Jae-Hyung et al. (2013) Green tea extract with polyethylene glycol-3350 reduces body weight and improves glucose tolerance in db/db and high-fat diet mice. Naunyn-Schmiedeberg’s Archives of Pharmacology DOI: 10.1007/s00210-013-0869-9
  12. Peters U, Poole C, Arab L (2001) Does tea affect cardiovascular disease? A meta-analysis. Am J Epidemiol.2001;154:495–503. (http://aje.oxfordjournals.org/content/154/6/495.full.pdf)
  13. Seeram NP, Henning SM, Niu Y, et al. (2006) Catechin and caffeine content of green tea dietary supplements and correlation with antioxidant capacity. Journal of Agricultural and Food Chemistry54(5):1599–1603.[PubMed Abstract]
  14. Steele VE, Kelloff GJ, Balentine D, et al. (2000) Comparative chemopreventive mechanisms of green tea, black tea and selected polyphenol extracts measured by in vitro bioassays.Carcinogenesis2000; 21(1):63–67. [PubMed Abstract]
  15. Zaveri NT. (2006) Green tea and its polyphenolic catechins: Medicinal uses in cancer and noncancer applications.Life Sciences78(18):2073–2080. [PubMed Abstract]