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.
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I don't take anti-oxidants to avoid cancer, i take them so i won't rust!
Don't you mean 'ignore pseudoscientific marketing claims'?
Welcome! As a lurker here, and a physician who thinks tox is cool, I look forward to reading your posts.
Just to clarify, as Im sure you know, one of the antioxidant theories (never proved) is to prevent, not cure cancers. Oxidative killing of cancer cells is good, healthy cells get in the way. But oxidative free-radical damage to cellular DNA can be bad (but is usually neutral). The idea of so-called antioxidants is to prevent this damage, therefore interrupt one of the "hits" of the two-hit hypothesis.
Of course, if you want to take beta-carotene as one of your antiox's, you better hope you don't have an occult lung cancer...they like b-carotene.
Not trying to troll here, but I'd expect better from a blog named the angry toxicologist. Your body uses pro-oxidative substances all the time as apart of the immune response('inflamation'). The fact that EGCG has a pro-oxidant reaction isn't all that crazy, nor are the population studies linking it's action to an anti-cancer effect. The reason being is the very anti-oxidant you mentioned, superoxide dismutase, which, if I'm not mistaken, tends to be found in highest concentrations in healthy mitochondria. Mitochondria produce most of the free radicals in your body, so you better be happy that there are some anti-oxidants nearby.
Mitochondria are funny organelles in that they tend to be turned off in many types of cancers. After all, mitochondria hold the self-destruct button, so if you're a smart cancer cell you'd turn them off so they don't blow you up. No active mitochondria, less superoxide dismutase, less superoxide dismutase means more damage done by EGCG.
The anti-oxidant theory of cancer is pretty weak to begin with, but just because you can show a hole in the theory(which I don't think many real cancer researchers buy anyway) that any type of 'anti-oxidant' is good for you, doesn't mean you can dismiss population studies or placebo controlled trials(if there is any of the latter, I believe those are currently ongoing). Further, the dangers of drinking over 10 cups of green tea a day have already been elucidated, and many green tea supplements are more around the 4-8 cup a day strength. By claiming that any supplement form of green tea is dangerous just because it can become toxic in high amounts is falling dangerously in line with the thinking of organic food eaters who try to avoid trace amounts of pesticide residue because in much higher amounts it can cause toxicity.
I'm not sure what the point of the above post was. I also am not sure what he meant about the mitochondria. My cellular bio is a bit rusty, but if you turn off all the mitochondria in a cell, it's dead.
And yes, apoptosis can be initiated in the mitochondria, which is one way of controlling cell proliferation, but I'm not aware of this "turn off the mitochondria" thing to interrupt apoptosis. There are other ways in which apoptosis can be inhibited in cancer cells, an area of active research.
JGraham,
I think you're missing the point. The point is that everyone (including the anti-cancer people) are touting it as anti-oxident and it's not one. Especially for people who don't have cancer, this can be a dangerous lie. Also, your chastisement about "dose makes the poison" is a bit off. First, I note that drinking tea is fine, it's the concentrated supplements that are a problem. Sencond, you might want to read up on some of the research coming out on low-dose toxicity of OP pesticides; I think you climbed up the wrong tree.
As with PalMD, I'm not buying the mitchondria shut down. Your idea about how cancer cells would be more sensitive to pro-oxidents is completely backwards. In fact, most cancer cells are VERY resistant to dying due to oxidative stress. That's the hallmark of a cancerous cell, it has overcome the signals that tell it that it's time to die.
Please also see the later post on the tea trials, which don't really show much.
I thought I had made that point, but perhaps I wasn't clear. I was responding to the fallacy listed by the other poster.
Cancer cells don't "turn off" mitochondria. The apoptotic pathway can become compromised, but if you were to shut down the mito's the cell would be dead.
The mito thing just doesn't make biologic sense. Cancer cells find ways to escape proliferation controls, such as apoptosis, but they don't "turn off" mitochondria.
I have a feeling I'm being terribly unclear.
PalMD, Your post was clear. I actually was agreeing with you ("As with" not "As for"). Perhaps I should have written "In agreement with PalMD".
Tell you what. Why don't we have a couple of more posts trying to 'argue' the functionality of mitochondira in cancer cells to each other and we'll have enough for a textbook entry. :)
I hate when I'm arguing about agreeing.
Thx.
thanks..
thought I had made that point, but perhaps I wasn't clear. I was responding to the fallacy listed by the other poster.
Cancer cells don't "turn off" mitochondria. The apoptotic pathway can become compromised, but if you were to shut down the mito's the cell would be dead.
I like the wizard of oz...I like the tin man.
The dangers of drinking over 10 cups of green tea a day have already been elucidated, and many green tea supplements are more around the 4-8 cup a day strength.
hello admin thanks for you site good Please also see the later post on the tea trials, which don't really show much.
hello 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: