Susan Jeffrey

November 11, 2008

November 11, 2008 (New Orleans, Louisiana) — Results of a small randomized trial show that 3 cups of hibiscus tea daily for 6 weeks reduced systolic blood pressure (SBP) by about 7 mm Hg in prehypertensive and mildly hypertensive subjects.

Among those with SBP over the median of 129 mm Hg, the reduction was double that, almost 14 mm Hg after 6 weeks, and produced significant reductions in diastolic and mean arterial pressures.

The finding "suggests that regularly incorporating hibiscus tea into the diet may actually help control blood pressure in people who are at risk for developing hypertension," said lead author Diane L. McKay, PhD, from the Jean Mayer USDA Nutrition Research Center on Aging at Tufts University, in Boston, Massachusetts, at a press conference here.

On a population basis, even small changes such as those seen in this study would be expected to reduce stroke, coronary artery disease, and all-cause mortality, Dr. McKay added.

The findings of this trial, which was supported by the Agricultural Research Service of the United States Department of Agriculture (USDA) and by Hain Celestial Group, makers of the Celestial Seasonings brand of herbal teas, were presented here at the American Heart Association 2008 Scientific Sessions.

Bioactive Phytochemicals

Hibiscus is among the most common ingredients found in herbal tea blends sold in the United States, Dr. McKay said. The principal components of hibiscus include anthocyanins and other flavanoids, as well as polyphenolic compounds and phenolic acids.

A variety of bioactivities have been attributed to these compounds, she noted, including the ability to act as an angiotensin-converting–enzyme (ACE) inhibitor. Earlier short-term trials in humans used black tea as a control, which also has an effect on vascular reactivity, making it not a proper control to look at the effects of hibiscus tea, she pointed out. "It is also interesting to note that a study comparing hibiscus tea with captopril, an ACE inhibitor, found no difference in blood pressure–lowering effects."

The aim of their study, she said, was to determine whether hibiscus tea, "in an amount that can be readily incorporated into the diet," will lower blood pressure in prehypertensive and mildly hypertensive adults compared with a placebo beverage.

The study was a randomized, double-blind, placebo-controlled trial of 65 generally healthy men and women aged 30 to 70 years who had SBP readings of 120 to 150 mm Hg and a diastolic blood pressure (DBP) of < 95 mm Hg.

Subjects were not taking antihypertensive medications or other supplements or medications that could affect their blood pressure level. They were not excluded on the basis of body-mass index (BMI), and BMIs in the study ranged from 18.5 to 34.9.

Participants were randomized to receive either three 8-oz servings daily of hibiscus tea for 6 weeks or a placebo beverage. The hibiscus tea was prepared by brewing 1 tea bag containing 1.25 g of dried hibiscus calyces in 8 oz of boiled water for 6 minutes, after which the tea bag was removed. The placebo beverage was prepared by adding a small amount of hibiscus-flavored concentrate to 8 oz of water.

The beverage had to be consumed within 12 hours of preparation and could be served hot or cold and with or without milk and a sweetener of the subjects' choice, she noted. The placebo beverage had no anthocyanins, which they believe is the active component, Dr. McKay pointed out.

Outcomes of interest were the change from baseline in SBP, DBP, and mean arterial pressure (MAP).

"After 6 weeks, we found that subjects who consumed hibiscus tea had a significantly lower systolic blood pressure level compared with people in the placebo group," said Dr. McKay. A drop in DBP and MAP was also seen, but these changes were not significantly different from placebo.

Blood Pressure Change at 6 Weeks With Hibiscus Tea vs Placebo

Blood Pressure

Hibiscus Tea, Mean Baseline BP Hibiscus Tea, Change Placebo, Mean Baseline BP Placebo, Change
SBP (mm Hg) 129.4 -7.2 129.8 -1.3
DBP (mm Hg) 78.9 -3.1 79.6 -0.5
MAP (mm Hg) 95.7 -4.5 96.3 -0.8

size="1">SBP = systolic blood pressure
DBP = diastolic blood pressure
MAP = mean arterial pressure

However, in a subgroup analysis of subjects with systolic pressures higher than 129 mm Hg, the magnitude of the change found with hibiscus tea was almost double that seen in the overall group, and differences with placebo with regard to systolic, diastolic and mean arterial pressure were all statistically significant, Dr. McKay said.

Blood Pressure Change at 6 Weeks With Hibiscus Tea vs Placebo in Subjects with Baseline Systolic BP > 129 mm Hg

Blood Pressure Hibiscus Tea, Mean Baseline BP Hibiscus Tea, Change Placebo, Mean Baseline BP Placebo, Change
SBP (mm Hg) 133.8 -13.2 135.7 -1.3

size="1">SBP = systolic blood pressure

Dr. McKay put their findings into the context of previously published work suggesting that, on a population basis, a reduction of 3 mm Hg in systolic blood pressure would be expected to translate into a reduction in stroke mortality of 8%, of 5% in coronary heart disease mortality, and of 4% in all-cause mortality (Whelton PK et al. JAMA. 2002;288:1882-1888).

During her presentation, she was asked by an audience member about any potential adverse events from this amount of hibiscus tea.

No adverse effects were reported, she responded. "There are some data from Nigeria, where we know that the average per capita consumption of a hibiscus-containing beverage is about the equivalent to 25 cups of our hibiscus tea every day, and no adverse effects have been demonstrated."

The study was funded by the Agricultural Research Service of the USDA and by Hain Celestial Group. The authors report no disclosures.

 

American Heart Association 2008 Scientific Sessions: Abstract 3278. Presented November 10, 2008.

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