|Mckay, Diane -|
|Chen, C-Y (Oliver) -|
|Saltzman, Edward -|
|Blumberg, Jeffrey -|
Submitted to: American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 20, 2009
Publication Date: February 1, 2010
Citation: Mckay, D.L., Chen, C., Saltzman, E., Blumberg, J.B. 2010. Hibiscus sabdariffa L. tea (tisane) lowers blood pressure in prehypertensive and mildly hypertensive adults: a randomized, placebo-controlled clinical trial. American Journal of Clinical Nutrition. 140(2):298-303. Interpretive Summary: This report details the first randomized, double-blind, placebo-controlled clinical trial to examine the blood pressure-lowering effects of consuming 3 c of Hibiscus sabdariffa tea daily for 6 wk in pre- and mildly hypertensive adults, age 30-70 y. In our analysis of the 65 participants who completed the trial, we found the change in mean systolic blood pressure of those who consumed the tea was significantly greater than in those who consumed the placebo beverage (-7.16 vs. -1.26 mm Hg, P < 0.03). The changes in diastolic blood pressure and mean arterial pressure (MAP) were also greater in the tea group, but were not statistically different from the changes observed in the placebo group. The blood pressure change observed in this trial was of greater magnitude than that reported in two large dietary intervention trials, i.e., DASH and PREMIER, which tested the blood pressure-lowering effects of a diet high in fruit, vegetables, and low-fat dairy products, and low in total and saturated fat. The compounds present in H. sabdariffa most likely responsible for the observed effects on blood pressure are the anthocyanins, delphinidin-3-sambubioside and cyanidin-3-sambubioside. Anthocyanins belong to the flavonoid family of phytochemical compounds and are responsible for the red, purple, and blue colors of many fruits, vegetables, cereal grains, and flowers. Studies suggest that anthocyanins exert their cardioprotective effects both directly and indirectly via multiple mechanisms. Potential mechanisms of action for the blood pressure lowering effect of H. sabdariffa were not determined in this study. However, in vitro and animal studies have shown that H. sabdariffa is a vasorelaxant, a diuretic, and an angiotension converting enzyme (ACE) inhibitor.Future research is warranted to determine whether H. sabdariffa has cardiovascular benefits beyond its demonstrated hypotensive effects. For example, although benefits have been suggested by the actions of anthocyanins from other foods, the effects of H. sabdariffa on outcomes such as cholesterol, inflammation, and oxidative stress have not yet been assessed in human studies.
Technical Abstract: Background: In vitro studies have shown Hibiscus sabdariffa L., an ingredient found in many herbal tea blends and other beverages, has antioxidant properties, and, in animal models, extracts of its calyces have demonstrated hypocholesterolemic and anti-hypertensive properties. Objective: To examine the anti-hypertensive effects of H. sabdariffa tisane (hibiscus tea) consumption in humans. Design: A randomized, double-blind, placebo-controlled clinical trial was conducted in 65 pre- and mildly hypertensive adults, age 30-70 y, not on blood pressure-lowering medications, with either 3 c/d of brewed hibiscus tea or placebo beverage for 6 wk. A standardized method was used to measure blood pressure (BP) at baseline and weekly intervals. Results: At 6 wk, H. sabdariffa treatment significantly lowered systolic BP (SBP) compared with placebo (-7.2 vs. -1.3 mm Hg, P < 0.030). Diastolic BP (DBP) was also lower, although this change was not significantly different than placebo (-3.1 vs. -0.5 mm Hg, P = 0.160). The decrease in mean arterial pressure (MAP) (-4.5 vs. -0.8 mm Hg) was of borderline significance (P = 0.054). No effects were observed with regard to age, gender, or dietary supplement use. In a subgroup analysis, subjects with higher SBP at baseline (>129 mm Hg, n=30) showed a greater response to H. sabdariffa treatment. Conclusion: Daily consumption of hibiscus tea, in an amount readily incorporated into the diet, lowers blood pressure in pre- and mildly hypertensive adults, and may prove an effective component of the dietary changes recommended for people with these conditions.