Three 240 mL servings a day of tea made with hibiscus (Hibiscus sabdariffa L.) were associated with a 7.2 mmHg reduction in systolic blood pressure and a 3.1 mmHg reduction in diastolic blood pressure, compared to 1.3 and 0.5 mmHg in the placebo group, according to findings published in The Journal of Nutrition.
Researchers from the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University report that this is the first placebo-controlled clinical trial to study if hibiscus tea, in an amount easily attained from the diet, may affect blood pressure.
“Hypertension is a major risk factor for cardiovascular disease and is associated with substantial morbidity and mortality, estimated to account for 35 per cent of myocardial infarction and stroke, 49 per cent of heart failure, and 24 per cent of premature mortality,” wrote the researchers, led by Dr Diane McKay.
“The dietary change assessed in this study, i.e. regularly incorporating 3 servings/d of hibiscus tea into the diet, effectively reduces blood pressure in pre- and mildly-hypertensive adults.
“This strategy may be useful in preventing the progression to moderate or more severe hypertension, potentially reducing the subsequent risk of developing cardiovascular disease,” they added.
Dr McKay and her co-workers recruited 65 adult with pre- and mild hypertension, and aged between 30 and 70, to participate in their randomised, double-blind, placebo-controlled clinical trial.
Subjects were randomly assigned to consume either three servings of brewed hibiscus tea per day or a placebo drink for six weeks. At the end of the study people in the hibiscus tea group displayed an average reduction of 7.2 mmHg in their systolic blood pressure, compared to 1.3 mmHg in the placebo group. A slight but not significant decrease in diastolic blood pressure was also recorded in the hibiscus tea group.
The benefits of hibiscus tea appeared to be greater in people who had higher systolic blood pressure at the start of the study.
Commenting on the potential mechanism, Dr McKay and her co-workers note that previous studies indicated that hibiscus may act by relaxing blood vessels, and this may be linked to calcium channels, or inhibition of the angiotensin converting enzyme (ACE), thereby preventing the conversion of angiotensin I to the potent vasoconstrictor, angiotensin II.
There is also evidence in the scientific literature that hibiscus may act as a diuretic. Another possible explanantion for the apparent benefits is related to the anthocyanin content of H. sabdariffa.
“The specific attributes of H. sabdariffa to cardiovascular health, including its ability to lower BP and its potential hypocholesterolemic effects, are not well understood and further research in this area is warranted,” added the researchers.
Source: Journal of Nutrition
February 2010, Volume 140, Issue 2, Pages 298-303
“Hibiscus sabdariffa L. tea (tisane) lowers blood pressure in pre-hypertensive and mildly hypertensive adults”
Authors: D.L. McKay, C.Y. Chen, E. Saltzman, J.B. Blumberg