Tea, one the most common beverages in the world, has intrigued both researchers and health-conscious consumers. Numerous studies discuss the benefits of tea, especially green tea, on various illnesses and metabolic problems. It's possible the benefits for hardening of the arteries, clotting and inflammation explain the decline in cardiovascular disease among heavy drinkers of green tea.
All types of tea come from the camellia sinensis plant. The differences stem from the way the leaves are dried and processed. The key active ingredients in green tea leaves are called flavonoids; they belong to the catechin family, whose most important member is epigallocatechin gallate. This is a powerful antioxidant, the source of many of the benefits attributed to green tea.
So how can green tea help?
Cardiovascular disease. Many studies show a link between tea consumption and the absence of disease. For example, in a 2010 study in the Netherlands, scientists followed more than 37,500 men and women for 13 years. A clear reverse association was found between tea consumption and death from cardiovascular disease and stroke.
Some studies did not show a clear pattern, but a 2011 analysis of 18 studies in the American Journal of Clinical Nutrition showed a 28 percent decline in the risk of heart disease among green tea drinkers. The study showed that consumption of one cup of green tea a day reduced heart disease by 10 percent.
Another meta-analysis on the link between tea consumption and strokes was published in 2009 in the journal Stroke, surveying five studies that followed nearly 195,000 subjects. It showed a 21 percent drop in the risk of stroke among subjects who drank three cups of green tea a day or more, compared to those who drank one cup less. But most of the studies were carried out in the Far East, where green tea consumption is more common than in the West.
Cholesterol. Studies show a decline in the rate of bad LDL cholesterol following consumption of green tea, without a major impact on the level of good HDL cholesterol or triglycerides. A 2011 analysis of 20 studies involving 1,415 subjects showed that consumption of between 145 and 3,000 grams of catechins over 3 to 24 weeks was accompanied by a decline of about 5 milligrams per deciliter of LDL. The mechanism by which catechins operate isn't clear, but they apparently reduce the absorption of cholesterol in the intestines.
Weight. A number of studies examined catechins' impact on weight and body fat. Most showed that green tea helps slightly in weight loss and reducing body fat.
Other effects. The main mechanism attributed to catechins, mainly to epigallocatechin gallate, is antioxidation. Many studies on lab animals and humans show powerful antioxidation against cholesterol. Although antioxidants' importance in preventing hardening of the arteries is still debated, some studies show that drinking green tea improves the elasticity of the arteries.
Prof. Yaakov Henkin heads the preventive cardiology department at Soroka Medical Center, Be’er Sheva.