This study identified and measured the effect of green tea and its extracts on levels of total cholesterol (TC), low-density-lipoprotein “bad” cholesterol (LDL-C), and high-density-lipoprotein (HDL) “good” cholesterol. The results of 14 previous studies involving 1,136 adults were analyzed statistically to estimate the effects of green tea on lipid profiles. Influences like the dose of tea, the time of the study, and an individual’s health were ruled out. The results suggest that intake of green tea significantly reduces levels of total cholesterol. It has no effect, however, on levels of HDL cholesterol.
High cholesterol (hyperlipidemia), a result of abnormal lipid metabolism, is widespread around the world. It is the most common cause of cardiovascular diseases and atherosclerotic plaques. A one percent reduction in blood lipids reduces the chances of a heart attack by three percent. Green tea is a popular brew made from fresh leaves of Camellia sinensis. It contains valuable nutrients including antioxidants, vitamins and minerals. Epidemiological studies indicate that increased consumption of green tea leads to a reduction in the risk of cardiovascular disease. Studies have shown that individuals who consume two cups of green tea per day have lower plasma total cholesterol levels. Their risk of death from cardiovascular disease is reduced by 22 to 33 percent. The chemical catechin, which is present in tea, helps reduce oxidative stress and inflammation of blood vessels, in addition to maintaining the balance of blood lipids like cholesterol. This paper analyzes previously published reports to correlate tea consumption with blood cholesterol levels.
* Research papers published between 1967 and 2010 were searched online as well as manually, by using search words related to “green tea” and “cholesterol”.
* Studies on human subjects with at least two weeks of tea consumption, baseline and endpoint records of cholesterol values, controlled diet, and blood-records were used.
* Information about the size of each study, health of each participant, and values of LDL, HDL, and total cholesterol before and after the experiments were extracted from the searches.
* Statistical analysis was carried out for the extracted data.
* For this meta-analysis, 14 published articles including 1,136 participants were used.
* Experiments varied from three weeks to three months. Green tea doses ranged from 150 mg/day to 2,500 mg/day. Five studies were on healthy individuals, five on obese adults, and four on patients with heart problems and high cholesterol levels. Trials varied in their designs, use of placebo controls and diet.
* Total cholesterol and LDL-C decreased markedly in participants who consumed green tea, but there was no difference in the HDL cholesterol levels.
* Subgroups were analyzed for possible influential factors like doses of tea and duration of study. These had no significant effect on cholesterol levels. Drinking grean tea lowered cholesterol levels in healthy as well as obese individuals. It also lowered them in patients with cardiovascular problems.
There was no general agreement on the exact quantity of tea that can be measured as one cup. Therefore, the doses of tea consumption varied widely across the studies. This means it isn’t possible to recommend an optimal dose of tea. Also, the presence of caffeine in green tea, which increases lipid levels in blood, may have influenced the results. Finally, the quality of the trials was inconsistent and safety data and side effects were not studied.
Drinking green tea (or using green tea supplements) decreases total cholesterol and LDL-C levels, but does not affect HDL cholesterol values. This effect is independent of the dose, duration, and the previous health status of the consumer. Reduced risk of death from heart problems in green tea drinkers had been demonstrated in previous studies. The chemical catechin in green tea is known to modulate blood LDL and HDL, the lipoproteins involved in transport of cholesterol into and out of blood. It may directly inhibit the production of cholesterol. The authors conclude that consumption of green tea reduces the risk of heart disease by lowering levels of blood cholesterol.
For More Information:
Green Tea Intake Lowers Fasting Serum Total and LDL Cholesterol in Adults: A Meta-Analysis of 14 Randomized Control Trials
Publication Journal: American Journal of Clinical Nutrition, 2011
By Xin-Xin Zheng; Yan-Lu Xu, The Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China