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Natural does not equal safe: green tea edition
By AngryToxicologist | May 10, 2007
Poison ivy, nightshade, cobras, green tea.
Uh, green tea?
Yeah, you heard me right. Don’t put down your cup of tea just yet, but if you’re near a GNC please run, don’t walk, the other way (good advice anytime).
A review ($) came out in one of my two favorite journals, Chemical Research in Toxicology (the other being VQR - you’ve got to keep your nerd in check), on the chemicals found in green tea that are supposed to so healthy, polyphenols. A bit of background first. The major polyphenols found in green tea called catechins have shown some anti-cancer activity in vivo (in a living thing). A lot of people speculated that this was due to the anti-oxidant power of the chemicals in vitro (outside a living thing, like in a petri dish) but the anti-oxidant function couldn’t be shown in vivo. Sounds a lot like the Vitamin C pill vs O.J. issue, no? (here, if you hadn’t seen it)
Here’s what has always been confusing to me, how are catechins supposed to be supporting cells, but killing cancer cells? The thing is, to kill cancer you’ve got to be toxic, how else do you kill something? The trick is to come up with something that’s really nasty to the tumor but not so nasty to the rest of the body. This dichotomy presents an extremely difficult challenge.
So how do catechins have it both ways? Well, turns out they don’t. The catechins turn out to be pro-oxidants in vivo! So much for the anti-oxidant theory. Let’s start small and go big to understand this:
Cells
Under cell culture conditions, one of the main green tea catechins (EGCG), is unstable and undergoes oxidative polymerization, generating hydrogen peroxide. As you can guess, bathing the cells of your body with hydrogen peroxide is, as we scientists say, bad. It’s reactive and bounces around the cell screwing up the structure of proteins and the cell membrane, among other things. Further tests showed that EGCG will destroy cancer cells but not if you add the anti-oxidant enzyme, superoxide dismutase (This enzyme surely wears a cape). You can see from name that it goes around undoing all the mutations the oxidation created. So the anti-cancer ability likely comes from the pro-oxidant function but cause the anti-oxidant stopped the killing.
Animals
Studies of green tea extracts/supplements on rats and dogs caused kidney, liver, and GI toxicity (suffice it to say liver and kidney cells were dying ugly deaths and there was bleeding in the GI tract). Toxicity and blood levels in dogs were much higher if they took the green tea on an empty stomach. The blood level effect is the same in people, which leads me to….
People!
There have been a number of case reports of liver toxicity related to consumption of tea-based supplements. In almost all the cases, enzymes that imply liver damage were elevated. Once the supplement was stopped, everything returned to normal. I guess because the researchers didn’t believe it, they started the supplement again and sure enough, the toxicity returned. There is some evidence that these and similar chemicals taken during pregnancy can lead to an increased risk of leukemia in the children. Lab study suggests that this may be due to the inhibition of a fetal enzyme that repairs damaged DNA. This still needs some work to fill in some knowledge gaps, but it’s enough to be concerned about.
What does all this mean?
Don’t take tea-supplements! I wouldn’t worry about drinking tea, though (in fact, I’m drinking a cup right now) as long as you’re not a 10 cup/day drinker. If you are, you should have already been worried about the caffeine, anyway. If you’re pregnant (congrats!), you should lay off the tea; many herbal teas are fine but I’d look over this first. There are many things out there that are fine for you, but when you make an extract or concentrate, it becomes harmful (think poppy seeds and opium).
Another interesting aspect of this is how everyone agreed that green tea had all these anti-oxidants when they were actually pro-oxidant. When are people going to get it into their heads that a couple petri dishes do not a body make? We have a hard time understanding the complexity of the body, much less being able to predict how chemicals will behave in it.
Take away: forget supplements, ignore scientific marketing claims, and try to eat healthy and exercise-it works better than any pill can.
Other products you have questions about? If there’s enough scientific evidence one way or the other, I’ll write about it while munching on a poppy seed bagel and drinking some tea. Send nominations to tox@angrytoxicologist.com.
Topics: food, Consumer Tox |
May 10th, 2007 at 1:49 pm
Does this mean all anti-oxidants are crap? I think I just spent way to much on an all-natural/anti-oxidant full sunblock.
Love the site!
May 10th, 2007 at 7:32 pm
What about cranberry juice?
May 10th, 2007 at 8:49 pm
Linda,
Anti-oxidants on the skin are probably one the few areas where I think they would work (the sun’s rays and the active ingredients in sunscreens create a lot of free radicals - basically the same thing as a oxidative state) so sun away in peace of mind.
Anonymous,
I’m not sure. No one has done a test on cranberry juice and anti-oxident activity like the OJ test I posted on (http://angrytoxicologist.com/?p=17). Cranberry juice is really beneficial for other reasons (urinary system health). People who have had kidney stones should avoid cranberry juice, though.
May 11th, 2007 at 12:21 am
I like your blog and respect your knowledge.
But if “tea-supplements” are the issue, why do you put a photo of gree tea at the top? I think that is sending exactly the wrong message.
May 11th, 2007 at 7:02 am
Good point. I couldn’t find a good picture (clear what the picture is of) of green tea supplements without a brand name in a hurry. If anyone’s got one that I can slap up, let me known (I try to stay away from brands unless I’m talking about that brand’s product specifically). I’m not e-phisticated to photoshop a brand name off a bottle either, or I’d do that.
May 13th, 2007 at 10:06 pm
The antioxidants don’t “kill cancer cells” while protecting normal cells. Oxidative genetic damage, which can lead to cancer, is inhibited by antioxidants.
May 14th, 2007 at 1:07 pm
That’s the whole point behind it. Anti-oxidants can’t kill cancer cells, which is what the catechins were found to do. The resultant research found that catechins were not anti-oxidants but actually pro-oxidants, which really throws the whole theory of taking catechins to protect against oxidation down the drain.
Apparently I didn’t write that clearly. Apologies.
May 19th, 2007 at 12:19 pm
Would taking aspirin daily counter the oxidative effect of green tea?
May 24th, 2007 at 8:43 pm
Actually, I disagree. Maybe it would be helpful to go back to your petri dish and review a few simple things about how cancer cells can be created and destroyed in a laboratory setting. Cancer cells can be created by depriving regular cells of oxygen. And guess what you can do to bring the whole thing back into balance? You must find a way to re-supply oxygen to the oxygen starved cells!
Hmmm… It looks like that whole pro-oxidation with antioxidants theory is starting to make some more sense, huh?
Regulating oxygen levels within the environment of a human body is a complex and multi-faceted process that’s interwoven with the delicate balance of pH levels present. In other words, it’s not really all that simple. I just wanted to explain my point in the most basic terms possible.
May 25th, 2007 at 12:10 am
More sense? um, no, sorry. Well, actually it’s a lot more complex than that. First, cancer cells in the lab behave nothing like cancer cells in the body. Second you can’t ‘re-balance’ the oxygen. If fact, I’m not even sure that has a meaning, biologically.
If you want to get indepth about it read this http://www.ovid.com/site/catalog/Book/698.jsp?top=2&mid=3&bottom=7&subsection=11
and although it’s getting a bit dated, this is still solid:
http://www.amazon.com/Growth-Oncogenesis-Molecular-Biology-Updates/dp/3764357274
May 25th, 2007 at 12:18 am
Bicycle Bruce,
I’m not sure if it would, but it’s possible. I recall a study 3-4 yrs ago that found that aspirin increased levels of paraoxonase-1 an antioxident enzyme. I wouldn’t suggest taking aspirin for this, but if you’re taking it for something else anyway it might help.
May 25th, 2007 at 6:44 am
Like I said, I am aware of the complexity involved. I thought that a simplification might be useful, but I guess not. Anyway, here is a really good article that outlines the minutia of details on how ECGC and other green tea catechins work to the benefit of human health.
May 25th, 2007 at 11:17 am
I don’t agree with their interpretations of the studies and some of the claims on that page are simply baseless, but that’s a bit off the point. The crucial difference is the difference between the tea and the supplements. Tea seems to be helpful, the extracts and supplements not so much. The fact remains that people that take green tea supplements have liver toxicity. All the lab results in the world don’t change that. Also, it’s important to remember that the whole point of the post was to talk about how our understanding has changed due to our greater understanding. This site is using some studies that we now understand led to the wrong conclusions. So again, drink that tea, but don’t take the supplements.
June 14th, 2007 at 2:40 pm
I believe that I’ve read that our immune system (white blood cells? I’m not sure) actually uses hydrogen peroxide to kill bacteria. I’m just guessing, but wouldn’t that be an example of our body using oxygenation for a very positive, protective activity? If we inhibited the production of hydrogen peroxide in our bodies we might never age but we’d die of raging infections from common bacteria (but with very smooth skin).
Also, on the whole oxygenation thing, seems like our body must be saturated with it, given the incredibly common nasty habit of breathing air that so many of us have. They told me in elementary school science class that we need oxygen, and that our body uses our lungs to extract oxygen from common air! A lot of old scientific notions have gone by the wayside, but I haven’t heard that this had changed. Why do we go to so much trouble to obtain oxygen constantly if it isn’t a “good thing”? And I understand that if oxygen is withheld “most” organisms return to room temperature very quickly. Maybe it would help global warming, if we weren’t contributing all this body heat to the biosphere?
Maybe this is a classic example of the axiom “every medicine contains a little poison”, and maybe we just ought to move on to a more useful and practical health obsession.
June 19th, 2007 at 12:51 pm
Of course oxygen is a good thing. But it’s a necessary evil. What you don’t want is other oxidants running around the cells because they do all the damage that oxygen can but provide none of the benefits that oxygen does (helping run cellular respiration, which is the main energy source for cells). Even with oxygen, you don’t want any more than you need.
October 23rd, 2007 at 12:52 pm
So, you are saying that this news article from webmd doesn’t have any value?
Green Tea May Aid Liver Disease Patients
NewsApril 23, 2002 — It’s already been shown to reduce the risk of heart disease and cancer, and now there’s evidence that the miracle brew — green tea — may help prevent transplant failure in people with liver failure.
Right now, there are far more people in need of a liver transplant than there are suitable donor livers. The problem is that donor organs usually become available due to accidents, and quite often, accidents involve alcohol. Livers subjected to excess alcohol are not good candidates for transplantation. They are too fatty — full of dangerous free radicals that make them susceptible to transplant failure, which can kill the recipient.
Free radicals are naturally produced in the body, and antioxidants help get rid of them.
Zhi Zhong, PhD, from the University of North Carolina at Chapel Hill, and colleagues looked at whether the powerful, free-radical scavenging antioxidants in green tea could alleviate some of the problems associated with fatty livers.
First, the researchers reproduced alcohol abuse in rats. After a bout of “binge drinking,” the drunken rats were put to sleep and their livers removed. These fatty livers spent 24 hours in cold storage, and then some of them were bathed in a solution containing green tea extract. The team then transplanted a group of rats with these seemingly unfit organs and others with normal, healthy livers.
Only 13% of the rats that received untreated fatty livers survived, compared with 88% of those that received healthy livers. In contrast, survival rate was bumped up to 77% for rats that received a fatty liver bathed in green tea extract.
Green tea extract scavenges harmful free radicals in fatty livers and therefore could be an effective treatment to prevent failure of liver transplants, according to the researchers.
October 28th, 2007 at 11:26 pm
I am probably one of the few people who actually have access to your cited article. I am alarmed when people cite esoteric, inaccessible articles and do not provide any data extracted from those articles to support their arguments. Case in point: the lethal dosage of EGCG in green tea according to the reference (Chem Res Toxicol 2007, 20, 583-5) consisted of 500 mg/kg po. Translation: the average over the counter green tea supplement may be standardized to contain 50 mg of EGCG. So, if your dog is medium size, say weighs 20 kg (probably the size of a beagle), you would have to give the dog 10,000 mg (10 grams), or 200 green tea pills per day for 13 weeks to cause kidney failure! Since the average sup of green tea provides about 25 mg of EGCG, this would be the equivalent of having your medium size dog drink 400 cups of green tea per day. For a good size man, 80 kg, he would have to drink 1,600 cups of green tea per day or take 800 green tea supplements to have this same dosage level.
Now, I am not saying that green tea does not have the potential to cause negative side effects, but let’s get our numbers straight here, people!
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February 5th, 2008 at 9:30 am
Love the site… very informative.
I drink alot of green tea, but only as a beverage - not as a nutritional supplement. Only recently have I seen all of the ads for the “green tea weight loss craze”. But, I was under the impression that green tea was lower in caffine than black tea - is that true??
April 29th, 2008 at 6:09 pm
Im confused im i supposed to stay away from green tea suppliments like pills etc ro from drinking green tea ? (I also have a problem with my liver so Im a bit worried)
May 27th, 2008 at 12:43 am
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