Effects of Green Tea on Cholesterol

By M. Park, PharmD

High cholesterol is one of the major health concerns affecting many people worldwide. According to the World Health Organization, about 39% of the world’s population has high cholesterol [1]. Cholesterol is one of the substances essential in maintaining the normal functions of the body, including the structuring of cells and production of hormones. High cholesterol, however, can lead to increased risk of heart disease and stroke.2 Current high cholesterol treatments primarily target Low Density Lipoprotein (LDL), which is often referred to as the “bad cholesterol.” LDL is known as “bad” because it carries cholesterol from the liver to body cells and often causes plaque buildup in the arteries [2].

Many clinical trials show an increased risk of heart disease when there is a raised level of LDL, making LDL the primary target of therapy [3]. Green tea contains potent antioxidants known as catechins, and its beneficial effects on cholesterol have been suggested by many epidemiological studies, clinical trials, and animal experiments. Lower levels in both total cholesterol and LDL were observed with consumption of green tea in many population studies [4]. The cholesterol-lowering effects of green tea have been suggested to be mediated by reduced absorption of cholesterol from the small intestine and its production by the liver [5, 6]. Through several animal experiments, catechins in green tea, especially Epigallocatechin gallate (EGCG) – the most abundant catechins – have been shown to interfere with intestinal absorption of cholesterol and production of LDL by the liver enzymes [5-7]. In addition to the cholesterol-lowering effects, some studies suggest catechins in green tea may also prevent plaque formation by LDL [7]. Although the exact process of plaque formation in the arteries is unknown, one of the proposed mechanisms involves LDL oxidation in the artery walls [7, 8]. LDL deposited in the blood vessels can react with free radicals and become oxidized.

Oxidized LDL causes direct damages and initiates an inflammation process involving the surrounding vessel walls, resulting in the buildup of more cholesterol as well as other substances including cell debris to the injured site of the blood vessel.

Then, over time, this “plaque buildup” causes narrowing and hardening of the vessels, and, depending on its severity and the tissues involved, it can cause a heart attack or stroke.8 Green tea catechins were shown to reduce LDL oxidation in several animal experiments, and these result suggest that catechins might play a significant role in reducing plaque formation [7, 9].

Current research suggests that green tea and its catechins may have beneficial effects on cholesterol, further reducing the risk of cardiovascular disease. More studies are still needed, however, to determine the clinical implications of these findings and to better understand their physiological effects on the human body.

References

1. World Health Organization. Raised Cholesterol. Retrieved from http://www.who.int/gho/ncd/risk_factors/cholesterol_text/en/index .html

2. National Heart Lung and Blood Institute. What is Cholesterol? Retrieved from http://www.nhlbi.nih.gov/health/health- topics/topics/hbc/

3. Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults. Executive summary of the third report of the National Cholesterol Education Program Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (ATP III). JAMA 2001; 285:2486-2497.

4. Zheng XX., Xu YL., Li SH et al. Green tea intake lowers fasting serum total and LDL cholesterol in adults: a meta-analysis of 14 randomized controlled trials. Am J Clin Nutr 2011; 94(2): 601-10.

5. Koo SI., Noh SK. Green Tea as Inhibitor of the Intestinal Absorption of Lipids: Potential Mechanism for its Lipid-Lowering Effect. J Nutr Biochem 2007; 18(3): 179-183.

6. Bursill CA., Abbey M., Roach PD. A green tea extract lowers plasma cholesterol by inhibiting cholesterol synthesis and upregulating the LDL receptor in the cholesterol-fed rabbit. Atheroscloerosis 2007; 193: 86-93.

7. Velayutham P, Babu A, Liu D. Green tea catechins and cardiovascular health: An update. Curr Med Chem 2008; 15(18): 1840-1850.

8. American Heart Association. Atherosclerosis. Retrieved from http://www.heart.org/HEARTORG/Conditions/Cholesterol/WhyC holesterolMatters/Atherosclerosis_UCM_305564_Article.jsp

9. Inami S., Takano M., Yamamoto M et el. Tea catechins consumption reduces circulating oxidized low-density lipoprotein. Int Heart J 2007; 48(6): 725-732.