Time for coffee and tea
Drinking tea and its effect upon blood pressure and endothelial function
The leaves of the plant, Camellia sinensis, are used to brew tea. There are many kinds of tea, and their differences lie principally in their ingredient profile. The most common are green teas (consumed primarily in China and Japan) and black teas (the kind more popularly used in Europe and the rest of the world). Tea is second only to water as the liquid most commonly consumed worldwide.
There have been a number of studies suggesting that tea has beneficial effects on the functioning of endothelial cells and on blood pressure. The main components responsible for these effects are thought to be the flavonoids in tea, which are antioxidant compounds.
The weight of the tea leaf, both in black and green teas, is comprised 35-40% by flavonoids. Because of the difference in oxidation of flavonoids, green tea has higher concentration of catechins, the main class of flavonoids found in tea. The level of catechins in black tea goes down below 10% as a result of continued oxidation of flavonoids.
On the other hand, black tea also becomes richer than green tea in flavonoid-oxidation products that result from the enzymatic processing of catechins. The enzymes polymerize the monomeric catechins, producing theaflavins and thearubigens which are also thought to be beneficial compounds. The different flavonoid composition in these two kinds of tea may produce different physiological effects.
The endothelium is a thin layer of cells that coat the inner lining of your blood vessels — the veins, arteries, the heart and the lymphatic vessels. Their normal function includes mediation of the blood clotting process (or coagulation), the functioning of the immune system, and controlling the volume of flow within, as well as immediately outside, the blood vessels. Endothelial dysfunction disrupts these biochemical processes. In endothelial dysfunction, the arteries particularly are unable to dilate fully, or open wider, even under proper stimuli.
One study assessed the effect of chronic (or over 4 weeks) consumption of tea on the dilatation of the important brachial artery in persons who suffered mild dyslipidaemia (a disease that causes endothelial dysfunction). The findings suggested that the effects of tea on dilation of the blood vessels were on the endothelium and also on the body’s ability to produce nitric oxide (a chemical that triggers vasodilation). A subsequent study on individuals with coronary artery disease (as they went through fasting and post-fasting stages) also showed that black tea improved flow-mediated dilatation but only when tea was taken together with a meal. There was little data on green tea, but the few data available do suggest that green tea improves endothelium-dependent dilation of the blood vessels.
These studies on the effect of tea on endothelial function provide some evidence that higher consumption of black tea and the flavonoids obtained from tea (green or black) may reduce the risk of developing cardiovascular disease, but this is not yet conclusive. Researchers believe more studies are needed to evaluate the effect of flavonoid metabolism on the endothelium. Until more definite results are obtained, you can continue drinking tea knowing that the chances of benefiting immensely from it are great.