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Tea and Cholesterol
Recent data are revealing that in addition to functioning solely as antioxidants, components in tea may be able to alter lipid levels. This reduction in cholesterol may be another key pathway by which tea is able to modify the risk of cardiovascular disease. A study published last year in The Annals of Epidemiology evaluated the effect of green tea consumption on serum lipids in a healthy Japanese population. More than 13,000 men and women aged 40 - 69 completed food frequency questionnaires and serum lipid panels over the course of 1 year. After controlling for confounding variables, the consumption of 1 cup of green tea was shown to be significantly and inversely correlated with a reduction in total serum cholesterol. This relationship appeared to be present in those consuming up to 10 cups/day, after which the relationship leveled off. Unfortunately, other studies in the US and Israel have failed to find such an association with tea consumption. The lack of findings from other studies may be a reflection of both the type and quantity of tea consumed as well as poor reporting of the exact method of preparation of the tea. Data presented at the Experimental Biology meeting held in 2002 in New Orleans, reported that the consumption of 5 cups/d of black tea for 3 weeks resulted in a 10% reduction in serum LDL-C compared with a placebo tea beverage. While the mechanisms that may be responsible for tea's ability to lower cholesterol are just beginning to be investigated, flavonoids have been shown to inhibit both HMG CoA reductase as well as acyl CoA:cholesterol acyltransferase activities (ACAT). HMG CoA reductase regulates endogenous cholesterol synthesis while ACAT catalyzes the esterification of cholesterol for the creation of lipoproteins. Inhibition of these enzymes could ultimately result in a reduction in circulating cholesterol levels. In addition to inhibiting these two enzymes, catechins present in tea have been shown to alter the secretion of apolipoprotein B (ApoB) in a cell culture model. Reductions in this lipoprotein component could alter the manner in which lipoprotein particles are secreted from the liver into circulation. Animal studies have also shown that tea catechins can reduce intestinal absorption of cholesterol as well as increase fecal excretion of fat and cholesterol.
The most compelling data on the ability of tea flavonoids to alter cholesterol levels comes not from the intake of a tea beverage, but from the study of a unique tea extract. Data from this recent study were presented at the American College of Cardiology meeting in March of 2003. In this double-blind, placebo-controlled trial, 240 men and women with mildly elevated cholesterol levels were given either 375 mg of a novel theaflavin-enriched green tea extract containing 20% theaflavins and 40% catechins (made via a unique controlled fermentation process of the tea leaves in which some of the catechins present in the green tea are converted to theaflavins) or a placebo for 12 weeks. Subjects in the group receiving the green tea extract experienced statistically significant 11.3 and 16.4% reductions in total cholesterol and LDL-C, respectively. Triglycerides were unchanged and HDL-C rose slightly in the supplemented group but was not statistically different from placebo. There were no findings of adverse effects or changes in routine blood chemistries. This report is among the first documentation of a tea-derived product having the ability to lower LDL-cholesterol in humans in a placebo-controlled trial. These clinical findings support the observational data on tea that has been previously reported.
For thousands of years drinking tea has played a significant role in many cultures, but only recently have researchers realized that tea may hold many more health benefits than previously thought. While the complex nature of tea makes it difficult to study, recent insights gained from both observational as well as controlled trials hint at the fact that we are only beginning to tap the full potential of this plant.
About Cholesterol |
Cholesterol is a molecule that is vitally important for many processes, including the stability and function of cellular membranes. Without cholesterol, our bodies could not be capable of synthesizing molecules such as CoQ10 or steroid hormones. However, data continue to mount demonstrating the deleterious effects of elevated cholesterol, especially elevated levels of LDL-cholesterol. In fact, data are now clearly showing that reducing elevated LDL-cholesterol can significantly reduce the risk for coronary heart disease. It is estimated that for every 1% reduction in LDL-cholesterol, there will be a 1.0 - 1.5 % reduction in the risk of major cardiovascular events. The third report of the National Cholesterol Education Program (NCEP), Adult Treatment Panel III, recommends that LDL-cholesterol reduction should be a target of lipid lowering therapy. Below is the NCEP Adult Treatment Panel III classification of cholesterol levels.
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References
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Hakim IA, Alsaif MA, Alduwaihy M, et al. Tea consumption and the prevalence of coronary heart disease in Saudi adults: results from a Saudi national study. Prev Med 36:64-70;2003.
Hertog MGL, Sweetnam PM, Fehily AM, et al. Antioxidant flavonols and ischemic heart disease in a Welsh population of men: the Caerphilly Study. Am J Clin Nutr 65:1489-1494;1997.
Hirano R, Momiyama Y, Takahashi R, et al. Comparison of green tea intake in Japanese patients with and without angiographic coronary artery disease. Am J Cardiol 90:1150-1153;2002.
Hodgson JM, Puddey IB, Burke V, et al. Regular ingestion of black tea improves brachial artery vasodilator function. Clin Sci 102:195-201;2002.
Maron DJ, Lu GP, Sheng CN, et al., "Theaflavin-enriched green tea extract lowers low-density lipoprotein cholesterol." Presentation 1057-146. American College of
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