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Registered User
Join Date: Jul 2005
Location: Spring, TX
Posts: 47
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Other benefits of green tea
Many of the ingredients in green tea are potent antioxidants. In vitro, green tea and/or EGCG prevent the development of or directly quench a variety of reactive oxygen species (ROS) including superoxide [55], peroxynitrite [56, 57], and hydroxy radicals [57]. In preventing lipid peroxidation by hydrogen peroxide, it was superior to both lipoic acid and melatonin [58]. In humans, acute administration of green tea significantly improves plasma antioxidant capacity [59-61], with 450 mL (which would contain about 375 mg EGCG) causing an increase of 12.7% after two hours in one study [61]. In turn, this enhanced protection against oxidative stress offers a variety of health benefits.
As discussed earlier, drinking green tea may delay death from cardiovascular disease by 1-2 years with a greater increase seen in men [31]. A study on 14,000 Japanese workers adjusted for dietary factors, age, BMI, alcohol consumption, tobacco use, coffee intake, and type of work found that green tea drinkers had significantly lower cholesterol levels [62] while a smaller study on 500 Japenese subjects found a statistically significant reduced risk of atherosclerosis in men, but not in women [63]. Although the present epidemiologic data does not support the idea that green tea increases HDL ("good") cholesterol in humans [62], it has been demonstrated that it does so in rats [64]. The data in this regard is still relatively preliminary so it is hard to draw too many conclusions, but the proposed mechanism of action for the delay in cardiovascular death is prevention of oxidative damage [57].
Due to its ability to increase superoxide dismutase and glutathione levels, green tea also may aid in the prevention of insulin resistance and type II diabetes [65], which is often closely interrelated with other cardiovascular conditions. In normal rats, green tea significantly increases glucose tolerance, while in diabetic rats it significantly reduces serum glucose [65]. Another study also found that green tea improved kidney function in diabetic rats [66].
Another area in which the activity of green tea is particularly important is in the brain. It goes without saying that green may protect against the development of brain tumors [67]. It also protects against oxidative damage in the brain [57] and improves brain recovery from ischemia/reperfusion injury in rats [68]. Green tea may also be useful in preventing Parkinson's disease through a fairly specific mechanism, and this has been an area of much study as of late [69].
Green tea also exert a protective effect in the liver, acting in a synergistic fashion with vitamin E [70], as well as the digestive organs. It protects against or lessens liver damage caused by alcohol and carbon tetrachloride in rats [71, 72] and protects liver cells from a variety of toxins in vitro [73]. In the gastrointestinal tract, it reverses intestinal damage induced by fasting in rats [74] and inhibits the production of a toxin (produced by Helicobacter pyroli) associated with some gastric diseases [75]. Other preliminary studies indicate that green tea may be useful in the treatment of arthritis [76] and cataracts [77].
Finally, recent cell culture studies have found that green tea may have strong antiviral activity. It has been tested sucessfully against influenza A and B and has been found to inhibit their growth [78], and it may also decrease the chance of HIV infection [79]. As of yet, it is unknown whether these observations are relevant in humans, in which the concentrations of the active ingredients wwould be much smaller.
Possible side effects and precautions
Green tea, even in large amounts, is associated with very few side effects. In mice, signs of toxicity were only observed when doses reached 2 g/kg daily of an 80% polyphenol abstract (this is about the equivalent of 8 cups per pound of body weight, per day – 1200 cups of tea in a 150 lb. individual) [80].
It is possible that large amounts of polyphenols could impair mineral absorption, making extra mineral supplements a wise course of action. Of primary importance is a significant inhibition of nonheme iron absorption, which is relevant if most of your iron comes from sources other than meat [81, 82]. It is possible that there is also mild inhibition of calcium, manganese, and zinc [83, 84], although there is a study that disputes the finding of impaired zinc absorption [84]. The only place where the phenomenon of significant mineral blockage by green tea has even been of worry is in Tunisia, where there is high tea intake and non-meat products are the primary source of dietay iron [81]. However, it may be prudent to take a multivitamin supplement that provides adequate amounts of these minerals at a separate time or a low-dose slow release iron supplement if one decides to consume large amounts of polyphenols.
A concern that is commonly brought up about green tea is the idea that it decreases levels of androgens such as testosterone and DHT. One study reported that after administered to rats, EGCG "significantly reduced food intake; body weight; blood levels of testosterone, estradiol, leptin, insulin, insulin-like growth factor I, LH, glucose, cholesterol, and triglyceride" [22]. However, a different study with green tea catechins in rats found decreased body weight but increased thyroid stimulating hormone (TSH), LH, and testosterone levels [85]. A final study in mice with green tea indicated drastic increases in both testosterone and DHT from green tea treatment, but levels of both were synergistically inhibited when it was adminstered along with soy phytochemicals [86]. In vitro, EGCG inhibits type I 5AR [2, 87], which is partially responsible for the conversion of testosterone to DHT (for this reason, it has been proposed in the topical treatment of acne and hair loss [2]), while in rats, green tea is an aromatase inhibitor, which (in theory) would be responsible for an increase in tesotsterone levels [85].
So, how does one make sense of this mess of contadictory data? It should first be noted that 5AR inhibition has only been shown in vitro [87], while it has not been observed in live animals – in fact, drastic increases in DHT have been found - and it seems that other constituents of green tea counteract the 5AR inhibition [88]. The conclusions of the first study, which found drastic decreases in body weight, testosterone, and other hormones, are very misleading. A drastic reduction in levels of all of the substances mentioned can unfortunately be expected from weight loss in any situation (which is one of the reasons losing weight without losing muscle mass is so difficult). Indeed, when the authors of the same study restricted the food intake of the rats to cause a similar weight loss to that induced by EGCG, similar effects were seen, implying that the changes were not due to EGCG but due to drastic body weight loss [22]. The effect green tea has on levels of androgens and other hormones is complex and depends on various factors, but no detrimental effects have as of yet been seen in human populations.
Green tea pharmacokinetics
This last section will examine the optimal dosage and dosing schedule for green tea. For cancer prevention, the present data indicate that relatively high amounts are required to achieve a significant effect – 10 cups or more per day [55, 88]. Luckily for those of us that do not have time to brew and drink ten cups of tea per day, there are supplements. (It has even been suggested that 10 cups a day in addition to supplements would be ideal for cancer prevention [89]). Ten cups is about 20 grams of tea leaves, which would contain about 2 grams of polyphenols, 1 gram of which would be EGCG. In comparison, 270 mg EGCG is all that is needed for significant fat loss [1], and this would still have positive health benefits. When we look at the pharmacokinetics of green tea, we can see that there may be ways to maximize the effect of a given amount. The most important thing to note is that green tea polyphenols undergo saturable presystemic elimination. This means that low doses only increase plasma EGCG levels marginally, but once the point of saturation is reached, the same amount of tea will have much greater effects.
The amount required to achieve saturation in humans varies from study to study. Using tea leaves, one study found 3.0 grams to increase plasma EGCG levels by 2.7-3.4 times as much as 1.5 grams, while the difference between 3.0 grams and 4.5 grams was not statistically significant [90]. However, a study measuring antioxidant potential of green tea leaves found that 2.5, 5.0, and 7.5 increased plasma antioxidant potential by 2.1%, 6.2%, and 12.7% respectively at the 120 minute mark, indicating that 7.5 grams was over twice as effective as 5.0 grams [61]. 7.5 grams equates to about 375 mg of EGCG (note that this is only an approximation), and a pharmacokinetic study with green tea extract yielded a similar result. Amounts containing 225, 375, and 525 mg EGCG raised plamsa concentrations by 657, 4300, 4410 pmol/mL, respectively [91]. However, in a last study, despite the fact that 400 mg EGCG (from an extract) overcame saturation as opposed to 200 mg (the AUC, in this case a measure of total bioavailability, was 23.0 and 64.9 respectively), 600 mg and 800 mg amounts kept getting significantly more effective, with AUCs of 111.1 and 258.2 respectively [92]. The maximum plasma concentrations similarly increased. It is also noteworthy that this study found that it took 600, not 400 mg of pure EGCG (without other catechins) to overcome saturation, once again emphasizing that the other catechins operate synergistically with EGCG.
With this data in mind, we could safetly say, for example, that taking an extract containing 400 mg EGCG once daily would be considerably more effective than 200 mg twice daily. Increasing this amount to 600 mg may or may not have a significant effect, depending on the study we look at. Either way, a minumum of 400 mg EGCG should be taken at a time to overcome saturation. An ideal dosing schedule would be 400 mg 2-3 times daily, while a more economical (but still very effective) one would be 400 mg once daily (preferably in the pre-workout period).
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