Results of a six-month intervention trial on 95 adult tea drinkers.
Black tea is a major contributor of dietary flavonoids to the global population and, like other dietary sources of flavonoids, it appears drinking the tea may have a positive effect on blood pressure.
Australian researchers recruited 95 adult tea drinkers for a six-month intervention trial. Participants were instructed to follow a low-flavonoid diet with the exception of black tea, which was assigned at three cups daily during a four-week run-in period. After the four weeks, participants were assigned to consume three cups of black tea solids (containing 429 mg of polyphenols and 96 mg of caffeine) or flavor- and caffeine-matched placebo daily for six months.
Those who consumed black tea solids experienced mean reductions in systolic blood pressure by 2.7 mm Hg and 2.0 mm Hg at three and six months respectively, compared to baseline. Diastolic blood pressure also decreased, with drops of 2.3 mm Hg and 2.1 mm Hg at three and six months. Between-group differences in gender, starting blood pressure, age, and other key variables were considered by the researchers to be insignificant.
Previous intervention trials with black tea have failed to observe a blood pressure benefit, wrote the researchers behind this new study. But they believe those studies may have been too low-powered and time-constrained to detect a benefit. The results of the new trial, published in the journal Archives of Internal Medicine, reflect what could be a serious benefit to tea drinkers at large.
“At a population level, the observed differences in [blood pressure] would be associated with a 10% reduction in the prevalence of hypertension and a 7% to 10% reduction in the risk of cardiovascular disease,” the authors said.
Funding for the study was provided by the National Health and Medical Research Council of Australia and Unilever (Vlaardingen, the Netherlands), which owns the Lipton tea brand.