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:
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.
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….
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 firstname.lastname@example.org.