Over the years, green tea has garnered a reputation for being a potent superfood, and it’s worthy of its reputation. People have  been drinking it for 5000 years, and in vivo animal trials and epidemiological studies have attributed the following health benefits to green tea consumption:

• Prevention of all causes of death
• tumor suppression
• increased concentration and brain activity
• protection against neurodegeneration
• prevention and reversal of metabolic syndrome
• free radical scavenging
• obesity and cancer prevention
• reduction in LDL cholesterol levels

Not too shabby. What’s even more remarkable is that most (but not all) of the benefits of green tea have been attributed to a class of molecule called catechins.

Catechin Health Benefits

Catechins are naturally occurring polyphenols commonly found in chocolate, green and black tea, red wine, and a few other plant foods. They seem to exhibit their positive health effects by scavenging free radicals and regulating DNA function in cells, and perhaps through a few other mechanisms that are not very well understood.

Green tea is a potent source of catechins. Commercially processed green tea is typically heated with steam or pan fried, which actually increases the catechin concentration in the tea leaves by activating heat-sensitive oxidative enzymes. By weight, green tea leaves are about 30-40% catechin concentration, compared to 10% for black tea.

Green tea has four classes of catechin molecules: epicatechin (EC), gallocatechin (GC), epigallocatechin (EGC), epicatechin gallate  (ECG) and epigallocatechin gallate (EGCG). That’s a confusing jumble science-y sounding jibberish, and you need not remember their names, but those four molecules are the workhorse of green tea’s life-enhancing properties.

Green Tea Catechins and Cancer Prevention

A lot of in vivo (living organism) animal studies repeatedly suggest that catechins can help prevent and in some cases reverse abnormal cell growth. The good news is that these results have proven to be very robust and have been repeated in different circumstances with different animals and with different conditions and the results have been consistent. The bad news is that the amount of catechins ingested by study participants are typically much higher than those found in the common diet, and it’s unclear how potent catechins are in promoting cellular health at lower dosage levels. This would provide a good rational for taking a green tea catechin supplement. Epidemiological studies on green tea consumption have results that are more mixed than in vivo animal studies.

To save some time, here are two links from the Journal of Nutrition that summarize the results of 38 different animal studies conducted with hamsters, mice, and rats with intestinal, colon, lung, prostate, breast, and liver cancer. The results are varied, but all have the common denominator of reducing cancerous bio-markers in the test subjects.

1. http://jn.nutrition.org/content/134/12/3431S/T2.expansion.html
2. http://jn.nutrition.org/content/134/12/3431S/T1.expansion.html

How green tea catechins protect against carcinogenesis is not entirely understood, but there are a few well supported hypotheses.

The catechin ECGC in particular seems to be the most potent tumor suppressing molecule found in the tea leaves. Many studies have found that cancerous cell lines treated with ECGC extract will go into remission and sometimes even reverse themselves.

Catechins seem to reduce oxidative stress within the body, but it’s not entirely understood why this occurs. The first notion was that green tea catechins scavenge harmful free radicals, but it looks now as if that view is over-simplified. Currently it appears as if polyphenols activate certain  enzymes within the cell that set off a series of redox reactions that changes its oxidative state.

Effects on Metabolism

Green tea catechins have a positive effect on both lipid and carbohydrate metabolism. Green tea extract increases the absorption of triglycerides and cholesterol, and studies have shown that people who ingest green tea tend to excrete more fatty acids in their urine than those who don’t.  Other studies have shown that green tea catechins decrease plasma cholesterol, increase HDL cholesterol (the good kind) and decrease LDL cholesterol (the bad kind). However, in some of these studies the observed effects only take place at very high doses, making the benefits of modest consumption unclear.

In a few clinical studies conducted on rats, animals with Zucker syndrome (the rat version of type 2 diabetes) showed decreased levels of blood glucose and tri-glycerides and an improved insulin response.

Another well-cited study published in the Journal of Clinical Nutrition in 1999 found that people who regularly took green tea extract showed higher levels of energy expenditure over a 24 hour period with a higher baseline  metabolism and lipid oxidation (fat metabolism). This paper added credibility to the claim that green tea is “thermogenic” (a buzz word for something that boosts your metabolism).

Mental Benefits of Green Tea Extract

Another health benefit attributed to green tea is that it improves mental performance and protects against mental degeneration. Both of these claims have some truth to them. However, exactly how much truth is a little tricky because green tea also has caffeine, which has similar effects, so separating one from the other can be difficult.

Prevention of Neurodegeneration

As discussed before, green tea catechins are potent inhibitors of oxidative stress. Oxidative damage is the defining characteristic of brain aging and neurodegeneration found in mental diseases like Alzheimer’s and Parkinson’s, whose prevalence increases with age. Not surprisingly, many of the drugs that attempt to treat these disease mimic the anti-oxidizing functions found in polyphenols and other plant compounds.

The catechins found in green tea modulate a variety of signaling systems in the Central Nervous System (CNS) as well as a part of the brain called the hippocampus which controls spatial memory and emotional responses, among other things.

Improvements in Memory and Concentration

The same mechanisms that allow catechins to prevent mental atrophy also allow their consumption to promote modest improvements in mental performance over time.

Additionally, the presence of molecules called metabolites contribute to increased cognitive performance. Metabolites are chemicals in plants that allow them to adopt to environmental stimuli, but play no role in primary metabolic functions. Metabolites often play a key role in regulating the Central Nervous System (CNS) of plants and the insects that feed off them, and are hypothesized to help humans because of similarities in our biology.

Phenolic compounds comprise a wide variety of molecules, many of which are considered metabolites, and mediate signaling pathways in the CNS as well as improve performance on memory intensive tasks.

Availibility of Green Tea Catechins in Food and Supplements

If you’ve read this far, hopefully I’ve convinced you that green tea, and the catechins within their leaves are very good for you. Like really good.

So how do you consume an adequate amount?

Like I said before, one problem with the research done on green tea is that many of the studies use dosage levels that are much higher than what would normally be consumed in the diet, making the usefulness of their results dubious.

Furthermore, the phenolic kingdom is very diverse, and the bio-availibility of catechins and other phenolic compounds can vary greatly from one type of tea leaf to another depending on growing and manufacturing conditions.

Because of this uncertainty, the optimal quantity of green tea consumption is up in the air.

However, it’s worth noting that this uncertainty can be mediated both with regular consumption over long periods of time and/or a green tea extract supplement.

In epidemiological studies prolonged green tea consumption has a strong correlation to a decrease in metabolic diseases (the correlation is not as strong for cancer prevention), and green tea supplements have a greater catechin percentage by weight.

One study published in the American Journal of Clinical Nutrition in 2004 found that a green tea supplement increased the duration and intensity of the anti-oxidant activity of catechins compared with regular green and black tea.

Whatever method you choose, rest assured that the decision to drink green tea is a sound choice. No food is a wonder drug, but when taken regularly green tea helps with everything but the kitchen sink.

Sip, and enjoy!

References:

Mandel SA, Weinreb O, Amit T, Youdim MB. The importance of the multiple target action of green tea polyphenols for neuroprotection.Front Biosci (Schol Ed). 2012;4:581-98

(AssunA§A£o2010)

Assunção, M., Santos-Marques, M.J., Carvalho, F. & Andrade, J.P.

Green tea averts age-dependent decline of hippocampal signaling systems related to antioxidant defenses and survival

Free Radical Biology and Medicine, 2010, Vol. 48(6), pp. 831 – 838

(Crespy2004)

Crespy, V. & Williamson, G.

A Review of the Health Effects of Green Tea Catechins in In Vivo Animal Models

The Journal of Nutrition, 2004, Vol. 134(12), pp. 3431S-3440S

(Dulloo1999)

Dulloo, A.G., Duret, C., Rohrer, D., Girardier, L., Mensi, N., Fathi, M., Chantre, P. & Vandermander, J.

Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in humans

The American Journal of Clinical Nutrition, 1999, Vol. 70(6), pp. 1040-1045

(Henning2004)

Henning, S.M., Niu, Y., Lee, N.H., Thames, G.D., Minutti, R.R., Wang, H., Go, V.L.W. & Heber, D.

Bioavailability and antioxidant activity of tea flavanols after consumption of green tea, black tea, or a green tea extract supplement

The American Journal of Clinical Nutrition, 2004, Vol. 80(6), pp. 1558-1564

(Kennedy2011)

Kennedy, D.O. & Wightman, E.L.

Herbal Extracts and Phytochemicals: Plant Secondary Metabolites and the Enhancement of Human Brain Function

Advances in Nutrition: An International Review Journal, 2011, Vol. 2(1), pp. 32-50

(Lambert2003)

Lambert, J.D. & Yang, C.S.

Mechanisms of Cancer Prevention by Tea Constituents

The Journal of Nutrition, 2003, Vol. 133(10), pp. 3262S-3267S

(Mak2012)

Mak, J.C.

The Potential Role of Green Tea Catechins in Various Disease Therapies: Progress and Promise

Clinical and Experimental Pharmacology and Physiology, Blackwell Publishing Ltd, 2012, pp. no-no

(Mak2012b)

Mak, J.C.

The Potential Role of Green Tea Catechins in Various Disease Therapies: Progress and Promise

Clinical and Experimental Pharmacology and Physiology, Blackwell Publishing Ltd, 2012, pp. no-no

(McKayAugust2007)

McKay, D.L. & Blumberg, J.B.

Roles for Epigallocatechin Gallate in Cardiovascular Disease and Obesity: An Introduction

Journal of the American College of Nutrition, August 2007, Vol. 26(4), pp. 362S-365S

Sasazuki, S., Inoue, M., Miura, T., Iwasaki, M. & Tsugane, S.

Plasma Tea Polyphenols and Gastric Cancer Risk: A Case-Control Study Nested in a Large Population-Based Prospective Study in Japan

Cancer Epidemiology Biomarkers & Prevention, 2008, Vol. 17(2), pp. 343-351

Valcic, S., Timmermann, B.N., Alberts, D.S., Wächter, G.A., Krutzsch, M., Wymer, J. & Guillén, J.M.

Inhibitory effect of six green tea catechins and caffeine on the growth of four selected human tumor cell lines

Anti-Cancer Drugs, 1996, Vol. 7(4), pp. –