How tea effects your blood pressure

Tea, having been brewed from the leaves of the Camellia sinensis for almost 4000 years, is the most popularly consumed beverage worldwide, second only to water. Owing to the high consumption of tea, even small effects in persons could have a large effect on public health. Tea contains more than 4000 chemical compounds that may affect the human body in many aspects. There has been a growing interest in recent years in exploring the preventive effect of tea, especially polyphenolic flavonoids in tea, against cardiovascular diseases.

A link between tea drinking and blood pressure reduction has been postulated for decades in general health care. However, there are few studies regarding the long-term effect of tea drinking on the risk of hypertension, and the results of the few studies investigating the relation between tea consumption and blood pressure were rather conflicting. In epidemiological studies, a higher consumption of black tea was associated with a lower systolic blood pressure , while green tea intake was unrelated to blood pressure. 

Nonhabitual tea drinkers are at higher risk of hypertension than habitual tea drinkers, and there are a progressive reduction in risk associated with higher levels of tea consumption in daily intake. The threshold of tea consumption likely to be beneficial for reducing the hypertension risk is to consume green or oolong tea, 120 mL/d or more, for at least 1 year.

From the present investigated physiological and pharmacological action of various components of tea, caffeine is well-known to have a short-term pressor effect following immediate tea ingestion within 30 minutes, but this effect will not translate into significant alterations 60 minutes later. Another potentially interesting component of tea with respect to blood pressure is theanine (γ-glutamylethylamide), which is one of the major components of amino acids in green tea and one of the neurotransmitters in the brain. Theanine administration to spontaneously hypertensive rats significantly reduced blood pressure. The possible hypothesis could be the antioxidant and vasodilatory effect of polyphenols in tea. Hypertension is characterized by increased peripheral vascular resistance and may, therefore, be associated with endothelial dysfunction through either loss of endothelium-dependent vasodilator activity or enhanced endothelium-dependent vasoconstriction. Oxidative stress has been implicated in the pathophysiological features, including hypertension and atherosclerosis. Thus, it has been proposed that impairment of nitric oxide synthesis, or increased inactivated nitric oxide by superoxide radicals, may account for the increased peripheral vascular tone associated with hypertension. 
There has been much evidence demonstrated in vitro and in vivo that tea polyphenols possess a strong antioxidant effect. Among various plant extracts of vegetables, fruits, teas, nuts, herbs, and spices, the top 5 that exhibited the greatest relaxing ability of vascular smooth muscle are cinnamon, peanut skin, red apple skin, guava pulp, and green tea. Accordingly, the endothelial dysfunction in the pathogenesis of hypertension may be reversed by the antioxidant-rich and vascular smooth muscle–relaxing tea extracts.

4 weeks of black tea consumption improves endothelium-dependent flow-mediated dilation of the brachial artery in patients with coronary artery disease.

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