Time for coffee and tea
Drinking tea and blood pressure
Time and again, it has been bruited about that tea has many beneficial effects on health. This could be of great import as next only to water, tea is the liquid with the largest consumption worldwide. If there are any health benefits to be had from long term consumption of tea, any such physiological effects would have a wide impact on public health.
Many population studies have in fact led to the suggestion that long term consumption of tea may help minimize the risk of developing cardiovascular disease. These are only epidemiological studies, however, and they need to be validated by more rigorous intervention studies. Nevertheless, the findings are very encouraging.
A standard cup of tea contains about 30-50 mg of caffeine. The presence of caffeine would naturally lead to the supposition that tea will cause an increase in blood pressure.
But, studies in laboratories have indicated that tea flavonoids can reduce blood pressure, despite the transient increase in blood pressure caused by caffeine. The results, however, are not consistent.
A A Woman has her blood pressure checked: Photograph by Greater Louisville Medical Society.
For instance, black and green tea flavonoids appeared to regulate blood pressure increases in rats with hypertension, but another study using the same rat model found that green tea flavonoids had no effect on blood pressure. Studies have also shown that green tea appears to reduce blood pressure in rats fed with fructose (the sugar from fruits), but does not do so in salt-sensitive rats.
Nevertheless, population studies do suggest that long-term regular consumption of tea may lower blood pressure. In a study on Norwegian men and women, higher intake of black tea was linked with lower systolic blood pressure in the cohort. Another study showed the same favorable effects of tea consumption on systolic and diastolic blood pressure of older women.
In a study on men and women above age 20, in comparison with those who did not drink tea, the risk of hypertension went down 46% in those who drank 2-3 cups of tea per day, and 65% in those drinking more than 3 cups per day.
These findings give indications that tea could indeed reduce blood pressure, or, at the very least, prevent it from increasing, over time. However, these results need to be validated by more controlled trials to confirm that lowered blood pressure is the result of tea consumption and not lifestyle factors usually associated with tea consumption.
There really is a lack of data from controlled trials that study regular tea consumption over a longer period (over 4 weeks’ continuous intake). There are research data from intervention trials on short term (up to 4 weeks) regular consumption, and these do not show changes in blood pressure. It is possible that longer-term effects on blood vessel dilation have to happen first before blood pressure is affected.
The acute effects, or the immediate impact, of tea on blood pressure seems contrary to the effects of regular intakes. One reason for this could be the presence of caffeine in tea, as mentioned earlier.
One study in particular reported that one dose of tea with 180 mg caffeine caused blood pressure to rise almost three times more than the increase observed from 180 mg caffeine acting alone, but this test was conducted on people who had fasted and avoided caffeine for over 12 hours. The same researchers also noted that this response to the tea flavonoids was not as intense when the subjects also had meals to go with the tea.
The research studies so far point to indications that tea and its flavonoids may retard the development of hypertension and reduce blood pressure, but conclusive validation is needed. There is a particular need to investigate the longer-term effects of regular tea consumption on blood pressure.