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Green Tea and Cholesterol
Green tea is one of the most popular and proven herbal remedies. Its medical benefits have been demonstrated in multiple clinical trials. One of this benefits is its cholesterol-lowering effect. Studies have shown that the catechins in green tea are responsible for its effect on cholesterol and that they inhibit the absorption rather than metabolism of cholesterol. Read on to find out how green tea catechins lower cholesterol and what other cardiovascular benefits can be derived from consuming green tea.
Green tea is the most healthful of teas. It is prepared from the leaves of Camellia sinensis. To preserve the bioactive phytochemicals in green tea, the leaves of the plant are only slightly oxidized during processing.
Although green tea is native to China, it is now a common beverage all over Asia and, because of its medicinal effect, it is increasingly consumed in the West too.
Green tea is a nutritional powerhouse. It contains carbohydrates, lipids, amino acids and enzymes as well as essential minerals and vitamins (especially carotenoids and tocopherols). However, it is prized for its phytochemicals.
Most of the bioactive phytochemicals in green tea are sterols, bioflavonoids and polyphenols. Some of these are potent antioxidants. The most important antioxidant in green tea is EGCG (epigallocatechin gallate).
The antioxidant content of green tea is higher than those of wine, fresh fruits and vegetable juices.
Over the years, green tea has been the subject of a number of medical studies and clinical reviews. It has been investigated for possible anticancer benefits as well as its role in reducing the risk of cardiovascular diseases.
In addition, green tea is believed to promote weight loss by inducing thermogenesis.
Of the proposed and investigated health benefits of green tea, the one with the most clinical support is its hypocholesterolemic property. There is conclusive evidence that green tea can reduce the levels of total cholesterol and low-density lipoprotein (LDL) cholesterol in the body.
Another hypocholesterolemic benefit of green tea is its effect on body fat. Studies have confirmed that regular consumption of green tea can reduce the amount of fats stored in the body.
Regarding cholesterol, a review of available studies shows that green tea affects the various types of cholesterol differently.
In addition, these studies show that the hypocholesterolemic benefits of green tea on cholesterol level is minimal for those who are already taking medications to lower cholesterol levels.
Furthermore, these studies indicate that green tea affects the level of LDL or “bad” cholesterol more than HDL (high-density lipoprotein) or “good” cholesterol. In fact, more than a few studies failed to find any connection between green tea supplementation and HDL cholesterol.
Clearly, regular, long-term consumption of green tea is recommended because it produces the best results. However, adopting green tea into one’s diet later in life can still provide modest health benefits.
Finally, these studies suggest that both green tea beverage and green tea supplements can improve lipid profile although the former produces better results.
Experts believe that the major mechanism by which green tea reduces cholesterol level is by blocking its absorption in the intestine. The polyphenols, especially catechins, in green tea are responsible for this blockage.
A 1996 study published in Japan’s Journal of Epidemiology investigated the link between regular green tea consumption and serum lipids and lipoproteins in over 2,000 Japanese men.
By tracking the men’s consumption of green tea as well as diet and lifestyle by questionnaires, the researchers of the epidemiological study correlated the data with the lipid profiles of the men.
After adjusting for factors such as body mass index, alcohol consumption, cigarette smoking and exercise, the researchers found that green tea consumption reduced the serum levels of total cholesterol as well as LDL cholesterol.
However, the researcher did not find evidence to suggest that green tea consumption affected the levels of triglycerides or HDL cholesterol.
In a 1986 study published in the Journal of Nutritional Science and Vitaminology, a group of Japanese researchers investigated the effect of the catechin extract of green tea on lipid metabolism in a group of male rats fed cholesterol diet.
In that study, the rats were divided into 3 groups. Two groups were given a casein diet rich in cholesterol for 28 days. During this period of time, one group of rats was given 1% green tea catechins while a second group received 2% of the same catechins along with their diet. The third group received no green tea catechin and, therefore, served as control.
The result of the study showed that green tea catechins improved lipid profile in the two groups who received them. Specifically, green tea reduced the plasma levels of total cholesterol, LDL and VLDL cholesterol while raising HDL cholesterol.
A 2003 study published in the Archives of Internal Medicine also confirmed the hypocholesterolemic effect of green tea.
In that study, the researchers investigated whether theaflavin-enriched green tea can improve lipid profiles in people with high cholesterol levels.
Although theaflavin is a common polyphenol in teas, it is not found in green tea. However, it is related to EGCG, the most popular antioxidant in green tea.
For this study, the researchers recruited 240 adults suffering from mild to moderate hypercholesterolemia and placed them on low-fat diets. Each of these participants received either placebo or 375 mg of theaflavin-enriched green tea capsule every day for 12 weeks.
The results of the study showed that theaflavin-enriched green tea reduced total cholesterol and LDL cholesterol significantly while increasing HDL cholesterol to a lesser extent.
These 2 studies demonstrate that green tea can improve lipid profile. However, its effects on the cholesterol levels are not big enough. Therefore, green tea should be used as a supplement to lower cholesterol levels in combination with low-fat diet, exercise and cholesterol-lowering drugs.
A 1999 paper published in the journal, Life Sciences, detailed the work of a group of researchers who investigated the possible mechanism by which green tea lowered cholesterol.
The researchers determined whether green tea affected the metabolism or absorption of cholesterol.
First, they placed a group of rats on cholesterol-rich diets and then gave them Chinese green tea. The researchers then measured the activities of the 3 major lipid-metabolizing enzymes (fatty acid synthase, cholesterol 7-alpha hydroxylase and HMG-CoA reductase) as well as the fecal excretion of cholesterol and bile acids.
After giving green tea to these hypercholesterolemic rats for 8 weeks, the researchers confirmed that green tea can indeed lower cholesterol levels.
The results also showed that the activities of the 3 lipid-metabolizing enzymes remained unchanged. However, fecal bile acids and cholesterol excretions significantly increased following green tea supplementation.
This study showed that green tea improved lipid profile not by increasing the breakdown of cholesterol but by reducing the absorption of cholesterol and increasing its excretion from the body.
A 2008 study published in the Journal of Nutritional Biochemistry also arrived at this conclusion.
This study provided a deeper insight into how green tea may block the absorption of cholesterol. The authors of the paper cited in vitro studies that demonstrated that green tea catechins interfered with the processes required for the absorption of lipids from the gut.
The study also identified EGCG as the most important green tea catechin responsible for inhibiting lipid absorption.
EGCG and other catechins disrupt the emulsification, digestion and micellar solubilization of lipids.
These 3 processes are essential to the repackaging of dietary fat and cholesterol in the gut before they are absorbed into blood circulation.
By interfering with these processes green tea also prevents the accumulation of lipids in tissues. When lipids are not prepared for absorption, the body rapidly excretes them.
The authors concluded the study by recommending green tea or its catechin extracts as safe lipid-lowering agents.
Therefore, green tea catechins are among the natural cholesterol-lowering agents that have the advantage of clearing out cholesterol even before it is absorbed. This greatly reduces the negative impact of cholesterol because it is prevented from reaching systemic circulation.
The benefits of green tea and black tea on lipid profile and cardiovascular health was investigated in a study published in the journal FEBS Letters in 1998.
In this study, the researchers fed different groups of hamsters with normal or high cholesterol diets for 2 weeks. The hamsters were also given black or green tea. At the end of the study period, the researchers found that both teas improved lipid profile but green tea produced better results.
In addition, both teas reduced lipid oxidation especially the oxidation of LDL and VLDL cholesterol.
Lastly, the study showed that both teas reduced the levels of fibrinogen in the hamsters placed on normal diet but not in the high-cholesterol groups.
This study shows that green tea (and black tea) can improve cardiovascular health by its hypolipidemic and antioxidant properties with possible fibrinolytic benefits too.
In a 2000 study published in the journal, BioFactors, a group of researchers determined whether regular green tea consumption can lower the risks of cancer and cardiovascular health.
This lengthy Japanese study involved over 8,500 adults. At the end of the study, the data gathered showed that those who consumed over 10 cups of green tea daily had lower risks of cancer and cardiovascular diseases than those who consumed less than 3 cups.
The researchers concluded that regular and high consumption of green tea can delay the onset of cancer and improve survival among those suffering from cardiovascular diseases.
Another Japanese study published in the journal, BMJ, in 2005 investigated the benefits of green tea consumption on cardiovascular and liver health.
This epidemiological study involved over 1,300 men over the age of 40. The researchers collected data on the living habits, diets and daily green tea consumption of these participants and correlated those with results obtained from blood samples given by these men.
The results of the study showed that green tea reduced the levels of total cholesterol, LDL cholesterol and triglycerides while increasing HDL cholesterol level especially in men who consumed more than 10 cups of green tea daily.
In addition, green tea improved liver health by reducing the serum concentrations of hepatological markers such as ferritin and the enzymes responsible for amino acid metabolism.
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