Prior investigations present a mixed picture, but well-designed new study suggests the answer is “yes”
by Craig Weatherby
The results of population studies generally indicate that drinking tea helps prevent cardiovascular disease.
As the German authors of a review published earlier this year put it, “Consumption of green or black tea has been inversely associated with the development and progression of cardiovascular diseases.” In other words, people who drink the most tea tend to have lower risks of cardiovascular disease.
Most researchers who’ve probed the reasons for the apparent cardio-protective effects of tea have focused on the ability of its polyphenol antioxidants—especially one called EGCG—to prevent oxidation of LDL cholesterol in the blood.
Oxidized LDL cholesterol gets swallowed up by immune system cells called macrophages, which recognize it as something that shouldn’t be allowed to roam free in the bloodstream.
However, a heavy diet of oxidized cholesterol turns macrophages into so-called “foam cells,” which go on to help form the atherosclerotic plaques that clog arteries and cause heart attacks or strokes.
Green tea seems to prevent oxidation of LDL cholesterol quite effectively, while black tea has a mixed record in this regard. Interestingly, three years ago an American research team reported that a green tea extract enriched with a polyphenol from black tea (theaflavin) lowered blood levels of total and LDL cholesterol substantially in adults with moderately elevated cholesterol levels (Maron DJ et al 2003).
And just last month, the Portuguese team whose new study is summarized below reported that green tea reduced oxidation of the fats and cholesterol in volunteers’ blood (Coimbra S et al October 2006).
However, studies designed to discover whether tea can improve blood fat profiles—that is, lower levels of total and “bad” (LDL) while raising blood levels of “good” (HDL) cholesterol—show mixed results.
But this month, the aforementioned Portuguese group published positive results from their investigation into this question.
Portuguese find green tea enhances blood fat profiles
Researchers at the Universities of Porto and Beira Interior, led by Susana Coimbra, Ph.D., evaluated the effects of green tea on the blood lipid (fatty acid and cholesterol) profiles of 29 healthy people.
The volunteers, who ranged in age from 22 to 63, drank one liter (4¼ cups) of green tea every day for four weeks. The tea was brewed fresh every day, always under the same conditions (temperature, brewing time, and amount of tea).
To eliminate the impacts of prior tea drinking, the volunteers first spent three weeks drinking one liter of water a day, before spending the next four weeks drinking one liter of green tea a day.
While the tea regimen produced no significant changes in blood levels of triglycerides or an undesirable form of cholesterol called lipoprotein(a), Dr. Coimbra and her colleagues recorded significant improvements in key aspects of the participants’ blood lipid profiles:
- Most importantly, the ratio of total cholesterol to HDL cholesterol decreased by six percent
- LDL cholesterol levels dropped by an average of 8.9 percent in 90 percent of the subjects
- HDL cholesterol levels rose an average of 4 percent in 69 percent of the volunteers
The Iberian investigators hypothesized that the beneficial effects of green tea seen in this study trace to its catechin-class polyphenols. As we said, studies suggest that these antioxidant compounds can block oxidation of blood fats and cholesterol by reactive oxygen species (free radicals).
As they wrote, “Our data suggest that green tea drinking… protects against CVD [cardiovascular disease] by improving blood lipid profiles.”
- Coimbra S, Castro E, Rocha-Pereira P, Rebelo I, Rocha S, Santos-Silva A. The effect of green tea in oxidative stress. Clin Nutr. 2006 Oct;25(5):790-6. Epub 2006 May 15.
- Coimbra S, Castro E, Rocha-Pereira P, Rocha S, Santos-Silva A. Green tea consumption improves plasma lipid profiles in adults. Nutrition Research. 2006 Nov; 26(11): 604-607.
- Hernandez Figueroa TT, Rodriguez-Rodriguez E, Sanchez-Muniz FJ. [The green tea, a good choice for cardiovascular disease prevention?] Arch Latinoam Nutr. 2004 Dec;54(4):380-94. Review. Spanish.
- Lin JK, Lin-Shiau SY. Mechanisms of hypolipidemic and anti-obesity effects of tea and tea polyphenols. Mol Nutr Food Res. 2006 Feb;50(2):211-7. Review.
- Maron DJ, Lu GP, Cai NS, Wu ZG, Li YH, Chen H, Zhu JQ, Jin XJ, Wouters BC, Zhao J. Cholesterol-lowering effect of a theaflavin-enriched green tea extract: a randomized controlled trial. Arch Intern Med. 2003 Jun 23;163(12):1448-53.
- Miura Y, Chiba T, Miura S, Tomita I, Umegaki K, Ikeda M, Tomita T. Green tea polyphenols (flavan 3-ols) prevent oxidative modification of low density lipoproteins: an ex vivo study in humans. J Nutr Biochem. 2000 Apr;11(4):216-22.
- Princen HM, van Duyvenvoorde W, Buytenhek R, Blonk C, Tijburg LB, Langius JA, Meinders AE, Pijl H. No effect of consumption of green and black tea on plasma lipid and antioxidant levels and on LDL oxidation in smokers. Arterioscler Thromb Vasc Biol. 1998 May;18(5):833-41.
- Riemersma RA, Rice-Evans CA, Tyrrell RM, Clifford MN, Lean ME. Tea flavonoids and cardiovascular health. QJM. 2001 May;94(5):277-82. Review.
- Stangl V, Lorenz M, Stangl K. The role of tea and tea flavonoids in cardiovascular health. Mol Nutr Food Res. 2006 Feb;50(2):218-28. Review.
- Tijburg LB, Wiseman SA, Meijer GW, Weststrate JA. Effects of green tea, black tea and dietary lipophilic antioxidants on LDL oxidizability and atherosclerosis in hypercholesterolaemic rabbits. Atherosclerosis. 1997 Nov;135(1):37-47.
- van het Hof KH, de Boer HS, Wiseman SA, Lien N, Westrate JA, Tijburg LB. Consumption of green or black tea does not increase resistance of low-density lipoprotein to oxidation in humans. Am J Clin Nutr. 1997 Nov;66(5):1125-32.
- Vinson JA, Dabbagh YA. Effect of green and black tea supplementation on lipids, lipid oxidation and fibrinogen in the hamster: mechanisms for the epidemiological benefits of tea drinking. FEBS Lett. 1998 Aug 14;433(1-2):44-6.
- Zhao W, Chen J. Candidate foods in the Asia-Pacific region for cardiovascular protection: Oriental tea. Asia Pac J Clin Nutr. 2001;10(2):138-42. Review.