NHP Forum: Green tea packs powerful punch

It seems everyone is going green these days, including tea drinkers! From anti-angiogenesis to weight loss, the benefits of green tea are wide-ranging—which is why this month, we are looking at the greener side of tea.Cardiovascular diseaseGiven its antioxidant properties, it is not surprising that green tea is used to support cardiovascular health. Animal studies have shown that green tea inhibits oxidation of LDL cholesterol, intestinal absorption of cholesterol and dietary fat, and also has anti-atherosclerotic effects. In addition, there is evidence that green tea improves circulatory function by inhibiting smooth muscle proliferation and platelet aggregation, promoting vasorelaxation, and neutralizing free radicals.The cardiovascular benefits of green tea in humans have been demonstrated primarily by epidemiological studies. The large prospective Ohsaki trial in Japan (n=40,530) showed that green tea consumption of > 5 cups daily over an 11-year period reduced cardiovascular disease mortality by 26%. The largest reduction was observed for stroke (37%), in particular cerebral infarction (51%). These effects were observed after adjusting for lifestyle and nutrient differences.Early indicators are that green tea also helps reduce postprandial (but not fasting) triglycerides. One small, randomized triple-crossover trial measured the effects of tea catechins on postprandial plasma lipid responses in subjects with mildly elevated triglycerides. Subjects were randomized to receive either control (10 mg), moderate dose (224 mg) or high dose (674 mg) catechins three times daily along with a piece of bread spread with 20 g butter. Results showed that moderate and high doses of tea catechins significantly reduced the incremental area under the plasma triacylglycerol curves by 15.1 and 28.7%, respectively. Green tea also significantly inhibited rapid elevation of remnant-like particle cholesterol two hours post prandially. Thus, consumption of green tea may be useful in reducing lipid elevations after meals in at-risk populations.DiabetesEvidence of the benefits of green tea in diabetes patients is mixed. A two-month randomized controlled trial of 66 patients with borderline or active diabetes found no difference between the control group and the active treatment group (456 mg catechins daily) with respect to inflammation markers or insulin resistance. However, a proprietary green tea extract did produce a statistically significant drop in plasma glucose levels in a randomized controlled trial of 38 overweight post-menopausal women. And a retrospective cohort study reported that green tea drinkers (> 6 cups per day) had a 33% risk reduction for diabetes versus non green tea drinkers. The same study found no reduction in risk for black tea or oolong tea drinkers.CancerThe antioxidant properties of green tea are believed to be responsible for many of its anticancer benefits; however, other anticancer properties have also been suggested. EGCG has been shown in animal studies to inhibit angiogenesis, promote apoptosis of cancer cells, and prevent UV-related DNA damage.Most of the research on green tea use in cancer has focused on its preventive effects. Some of the findings reported so far: subjects who consumed more than 10 cups of green tea per day had lower total cancer incidence rates compared to those consuming fewer than three cups per day; women who drank more than five cups of green tea daily had half the risk of distal gastric cancer compared to women who drank less than one cup; and consumption of more than three cups of green tea per day before breast cancer diagnosis was associated with a decreased risk of recurrent disease. The Ohsaki trial also found that men who drank five or more cups a day of green tea were approximately half as likely to develop advanced prostate cancer compared to men who consumed less than one cup per day.Weight lossUnlike other areas of green tea research, most weight loss studies have utilized green tea solid extracts rather than brewed tea. A randomized, double-blind, placebo-controlled trial found that fat oxidation increased by 35% after supplementation with green tea extract. Another study compared placebo to green tea extract (270 mg EGCG + 150 mg caffeine) and to caffeine alone (150 mg). Caffeine alone stimulated the sympathetic nervous system, thus increasing energy expenditure (EE), while EGCG combined with caffeine increased EE more than caffeine alone. And despite the fact that green tea catechins increase fat burning, only one open-label trial has shown significant weight loss (4.6%) with a green tea extract.Safety and doseThe adverse effects and drug interactions associated with green tea are mostly theoretical and mostly related to its caffeine content. Theoretically, high doses of caffeine can raise blood pressure, but consumption of more than 10 cups of green tea daily has not been associated with increased blood pressure. There is also concern that green tea may have additive effects with anticoagulant drugs, but this interaction has not been proven in humans.Unfortunately, there is no consensus regarding the ideal daily dose of green tea. The Ohsaki study saw a 16% drop in all-cause mortality at five or more cups a day, so that is a reasonable recommendation for a daily preventive dose. As with all natural products, there can be substantial variation in quality from brand to brand: this is true for both teas and solid extracts. Advise patients that in order to reap the full benefits of this green revolution, they should ideally consume high-quality loose-leaf Japanese or Chinese green teas or green tea extracts backed up with human clinical data.Now, I think I’ll go brew myself a nice hot cup of green tea!Tracy Marsden is a pharmacist, natural medicine consultant and co-owner of Rocky Mountain Analytical, a CAM laboratory.Click here to get the facts on tea

NHP Forum: Green tea packs powerful punch

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