Thursday, April 26, 2018

Green tea catechins and liver damage

A report* about possible toxicity for the liver of green tea catechins at high doses has raised concerns among Friends of Pairteas, so I looked into the matter this week.

In the US green tea catechins are available over the counter as supplements. Drugs considered dietary supplements are not regulated in the US in any significant way for either safety, effectiveness, or dosage limits. 

Epigallocatechin gallate (EGCG), the major catechin in green tea. Image from Wikipedia.

A major problem in determining whether green tea extracts have any effect, either beneficial or adverse: people differ tremendously in how much catechin a person absorbs from a given dose of supplement (or brewed green tea, for that matter). One person may have up to 6 times more catechins in their blood than the next person with a given dosage!**

The reason for this huge difference may lie, at least in part, in genetic differences in a person's capacity to transport drugs and the products of their metabolism for excretion in the liver and kidney. When certain drugs fail to be cleared from cells due to transport problems they can damage mitochondria, and ultimately lead to cell death. This phenomenon may explain why catechins, which are metabolized and excreted by the liver, may cause liver damage.

The question is then: how much catechin is needed to cause damage? and how severe is that damage? and one more question: do catechins interact with other drugs/suplements?

We don't know the answers to any of these questions. 

The European white paper stems from a spate of case reports and animal studies that have suggested that liver damage with catechin supplements may occur. In the case of animals, huge doses were delivered over multiple years, so these studies should not be extrapolated to humans. 

With respect to humans, one study of case reports that really scared me concerned a supplement called Slimquick®, where a person had to have a liver transplant.*** 

But case reports are problematic because you can't exclude the possibility that other issues, such as disease, the use of other medications or supplements, or even the purity of the catechin supplements, aren't the real cause of problems. 

These are the reasons why Isomura and colleagues decided to review human randomized control trials of catechins.**** In these trials, catechin supplementation was compared directly with placebo or no treatment, so that one could decide with some degree of certainty that the catechins were responsible for any adverse effects. 

Of the 34 usable trials reviewed by Isomura and colleagues, liver-related adverse effects were found in only four. There were 8 adverse events among the people received catechins and one event in a person receiving a placebo.

Of these four trials with adverse effects, only one involved healthy volunteers. Of the others, one involved women with breast cancer, one men with prostate cancer, and the third post-menopausal women who may have taken other medications. In other words, we cannot say whether any of the condition in these three trials may have contributed to the adverse events. 

Furthermore, adverse events in these trials consisted of elevation of liver enzymes, but no active disease. That said, elevation of liver enzymes are indeed an indication of active liver damage. The liver happens to have a rather large, though not infinite, capacity to experience damage without long-term consequences. 

Bottom line: we really don't know at this point whether catechin supplements cause liver damage, to whom, and at what dose. But the amounts in your favorite cup of green tea come nowhere close to the amounts in supplements. 

My advice: enjoy your green tea as a drink in a cup for its taste and avoid "magical" supplements that promise life-changing effects. Liver disease would indeed be life-changing!

Incidentally, Cornell University hosts a National Institutes of Health database where you can look at the toxic effects of different drugs and supplements on the liver:

Longing tea steeping in a gaiwan. Image from Wikipedia.

* EFSA ANS Panel (EFSA Panel on Food Additives and Nutrient Sources added to Food), Younes M, Aggett P, Aguilar F, Crebelli R, Dusemund B, Filipič M, Frutos MJ, Galtier P, Gott D, Gundert‐Remy U, Lambré C, Leblanc J‐C, Lillegaard IT, Moldeus P, Mortensen A, Oskarsson A, Stankovic I, Waalkens‐Berendsen I, Woutersen RA, Andrade RJ, Fortes C, Mosesso P, Restani P, Arcella D, Pizzo F, Smeraldi C and Wright M, 2018. Scientific Opinion on the safety of green tea catechins. EFSA Journal 2018;16(4):523. 9, 89 pp.

** Scholl C, Lepper A, Lehr T, et al. Population nutrikinetics of green tea extract. Atkin SL, ed. PLoS ONE. 2018;13(2):e0193074. doi:10.1371/journal.pone.0193074.

*** Zheng, E.X., Rossi, S., Fontana, R.J. et al. Risk of Liver Injury Associated with Green Tea Extract in SLIMQUICK® Weight Loss Products: Results from the DILIN Prospective StudyDrug Saf (2016) 39: 749.

**** Isomura T, Suzuki S, Origasa H, et al. Liver-related safety assessment of green tea extracts in humans: a systematic review of randomized controlled trials. European Journal of Clinical Nutrition. 2016;70(11):1221-1229. doi:10.1038/ejcn.2016.78.

Thursday, April 19, 2018

Why does Earl Grey tea contain bergamot?

Have been lost in the weeds (or better said, tea leaves) putting together a course for World Tea Academy on blending teas with other flavor bearing elements. While I have been having a lot of fun discovering new ways of thinking about tea blending, a deadline looms...

But I can't resist telling you about Earl Grey tea. It's perhaps the most famous flavored tea in the West and traditionally combines a black tea with bergamot, either as peel or oil derived from the peel.

Image from Wikipedia, photo from the “Nürnbergischen Hesperidum - Volkamer”
by Johann Christoph - Nürnberg, 1714.
My exploration of Earl Grey tea led me to wonder: where did Lady Grey get the bergamot to add to the tea? Did she get it from Italy directly or from an orangery at her home, Howick Hall in Northumberland? (Orangeries were popular in 18th and 19th century noble houses—richly windowed buildings where the most exotic tropical and Mediterranean fruits could be grown successfully in frigid Northern climes.) This question led me to learn more about Howick Hall, built and rebuilt over the years starting in the 14th century.

Howick Hall, image from Wikipedia
While I still don't know whether Howick Hall had an orangery or not, I did learn that, of the many legends concerning the origins of Earl Grey tea's formulation, the one cited by the Howick Hall website is as follows: the addition of bergamot was suggested to the Earl by a Chinese envoy to counteract the lime (= calcium carbonate) content of the Hall's water. Water with a high lime content is more alkaline (higher pH) and of course has more calcium than pure water. 

It turns out that water high in calcium limits extraction of tea leaf compounds during brewing, leading to a tea with less caffeine and less amounts of polyphenols. This effect can be modulated by the acidity of the water, with greater acidity (lower pH) leading to greater extraction and less effect of the calcium. Bergamot's acidity would thus counteract this effect of calcium carbonate.

The other effects of calcium carbonate are on the extracted brew itself. As the tea cools down, "tea cream" develops—a turbidity that dulls the shine of the tea. Another problem is that the polyphenols continue to transform, yielding a more brown-orange and less red color. Look for this color change if you add milk to tea in a glass. Both of these transformations would make the tea less attractive to people who are used to a redder tea, with or without milk.

Black tea with and without milk—notice the color difference! Photo by Joanna Kosinska on Unsplash

But mostly, a lower pH yields a tea that simply tastes better.

Oh, and why bergamot instead of, say, lemon, which could accomplish the same goal?

I would imagine that it is because bergamot is more fragrant—and more exotic—than lemon. 

If you like your black tea better with lemon than without, now you know why.

==> Three Basic Teas & How to Enjoy Them, available in paperback and Kindle on Amazon!


Yong-Quan Xu, Chun Zou, Ying Gao, Jian-Xin Chen, Fang Wang, Gen-Sheng Chen, Jun-Feng Yin. Effect of the type of brewing water on the chemical composition, sensory quality and antioxidant capacity of Chinese teas. Food Chemistry, Volume 236, 2017, Pages 142-151, ISSN 0308-8146,

Chandini, S. K., Jaganmohan Rao, L. and Subramanian, R. (2011), Influence of extraction conditions on polyphenols content and cream constituents in black tea extracts. International Journal of Food Science & Technology, 46: 879-886. doi:10.1111/j.1365-2621.2011.02576.x

Wednesday, April 4, 2018

US League of Tea Growers and the aromas of tea

So excited about giving a talk via Skype about the development of tea aromas to the members of the US League of Tea Growers at their annual meeting in Mississippi. 

They will be hosted by Friend of Pairteas Jason McDonald of The Great Mississippi Tea Company. (Incidentally, their green tea won a silver medal among USA-grown teas at the Global Tea Championship last year, with a score of 93% in blind tasting!)

My talk will center around the aromas in teas and the processes by which they come into the cup. I'll emphasize time, temperature, and especially handling of the leaves as important for the development of the most delicious aromas. Here's one of the slides I prepared for the talk:

This slide shows compounds that emerge early in the processing of the tea leaves, and contribute to green tea flavor.

When a leaf is damaged, its cells immediately release hexanals—they give us the aroma of new-mown grass.

As injury and stress continue, leaves produce the three compounds in red—jasmonates, abscissic acid, and salicylic acid.  

Among its many functions, abcissic acid closes the stomata—the little "mouths"—on the underside of leaves that slow down water loss. You can easily imagine that large amounts of this compound are produced in the withering room! 

Notably, abscissic acid is also the precursor for the formation of nerolidol, the aroma compound that is the hallmark of high quality oolongs. The more punishment tea leaves experience when being transformed into oolongs, the more nerolidol is formed.*

Linalool and geraniol are normally stored as glycosides in the plant cell's central vacuole, far away from the enzymes that break up the glycosides. When the cell is damaged, the glycosides leak out of the central vacuole, come into contact with the enzymes, and the delicious cool rose-like aromas of linalool and geraniol waft in the air.

As for salicylic acid, it is the precursor for methyl salicylate. It takes time and a lot of processing for the leaf to form methyl salicylate, so you won't find it in green tea, only black. It is one of the compounds that give black tea is rich sweetness.

As for the green border around ß-ionone? As you may have seen me mention before, I can't smell this compound, and neither can some 40% of people of European descent. Pity, because people who can smell it say it smells delightfully floral!

Ying Zhou  et al. Formation of (E)-nerolidol in tea (Camellia sinensis) leaves exposed to multiple stresses during tea manufacturing. Food Chemistry 231 (2017) 78–86.

==>> Available on Amazon in paperback and Kindle: "Three Basic Teas & How to Enjoy Them."