A small Australian study, published in the journal Archives of Internal Medicine last month, has found that three cups of black tea a day may significantly lower blood pressure, reducing heart disease risk by as much as 10%.
The research, led by Dr. Jonathan Hodgson of the School of Medicine and Pharmacology, University of Western Australia, involved 95 men and women who were randomized to receive either three cups of black tea a day or a placebo that matched the tea in flavour and caffeine content.
The study group had blood pressure ranges that were broadly representative of the overall population, the average blood pressure at the beginning of the study was 121/72 mmHg with systolic blood pressures ranging from 115 mmHg (normal) to 150 mmHg (mildly hypertensive).
The ambulatory blood pressures of the participants were monitored throughout the 6 month study. The researchers found that the blood pressures of the tea group decreased significantly relative to the control. Systolic blood pressure was 2.7 mmHg and 2.0 mmHg lower at 3 and 6 months respectively, while diastolic blood pressure was 2.3 mmHg and 2.0 mmHh lower at 3 and 6 months. The authors calculated that this would be enough to reduce the prevalence of hypertension by 10% at a population level and would cut overall risk of cardiovascular disease by between 7% and 10%.
This isn’t the first study to find a link between black tea consumption and heart health. A 2003 study of 15 mildly hypercholesterolemic adults found that drinking 5 cups of black tea a day for 3 weeks resulted in a 6.5% reduction in total cholesterol and a 11.1% reduction in LDL cholesterol levels. The researchers concluded that “based on our study, the inclusion of tea in the diet has the potential to significantly reduce blood cholesterol and thereby reduce the risk of CVD”. Full results of that study can be found here.
A study, published in the journal Preventative Medicine in 2002, looked at the risk of coronary heart disease across varying levels of tea intake in a cohort of 3,430 Saudi men and women. The researchers found a significantly lower prevalence of coronary heart disease in those who consumed large amounts of tea daily. In the fully adjusted model, those who consumed more than 6 cups of tea a day had 51% lower odds of developing coronary heart disease compared to non drinkers.
Black tea is a rich source of flavonoids, which might explain the heart benefits of drinking the beverage. Flavonoids are believed to increase the synthesis of nitric oxide in the body. Nitric oxide is a powerful vasodilator meaning it relaxes the smooth muscle cells of the veins and arteries, widening blood vessels and thus reducing blood pressure. Flavonoids have also been shown to reduce plasma levels of endothelin-1 in laboratory studies. The over-expression of endothelin-1 has been linked to an increased risk of hypertension. Studies have also found a link between consumption of chocolate, which is rich in flavonoids, and small reductions in blood pressure. Other dietary sources of flavonoids include onions, red wine, citrus fruit, cranberries, strawberries, and tomatoes.
Black tea consumption rates vary substantially between countries. The largest consumers of black tea on a per capita basis include the UK, Ireland, Mauritania, Turkey, and Middle Eastern countries such as the UAE, Kuwait, and Qatar. Asian countries tend to drink a greater proportion of green tea rather than black tea.
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