Hibiscus sabdariffa, commonly known as Roselle is a member of the species of Hibiscus. It is an annual or perennial that is native to West Africa. The leaves and stems of Roselle are commonly used throughout the world as a tea.
The leaves of Roselle has been used medicinally for centuries and contain a large variety of polyphenols. The major identified compounds include: 1
- caffeoylshikimic acid
- chlorogenic acid
- cryptochlorogenic acid
- neochlorogenic acid
- protocatechuic acid
Figure 1. Dried Hibiscus sabdariffa (used in tea)
Extracts of the calyces of Roselle have demonstrated hypocholesterolemic and antihypertensive properties. The potential mechanisms for Roselle’s antihypertensive effects may be the antioxidant effects of the anthocyanins inhibition of LDL-C oxidation, which impedes atherosclerosis, an important cardiovascular risk factor. 2
There are five important researched studies that have found consumption of Roselle had antihypertensive effects and were able to lower systolic and diastolic blood pressure:
A study from February 2010 examined the antihypertensive effects of Hibiscus sabdariffa tisane (hibiscus tea) consumption in humans. A randomized, double-blind, placebo-controlled clinical trial was conducted in 65 pre- and mildly hypertensive adults, age 30–70 y, not taking blood pressure (BP)-lowering medications, with either 3 240-mL servings/d of brewed hibiscus tea or placebo beverage for 6 wk. A standardized method was used to measure BP at baseline and weekly intervals. At 6 wk, hibiscus tea lowered systolic BP (SBP) compared with placebo (−7.2 ± 11.4 vs. −1.3 ± 10.0 mm Hg; P = 0.030). Diastolic BP was also lower, although this change did not differ from placebo (−3.1 ± 7.0 vs. −0.5 ± 7.5 mm Hg; P = 0.160). The change in mean arterial pressure was of borderline significance compared with placebo (−4.5 ± 7.7 vs. −0.8 ± 7.4 mm Hg; P = 0.054). Participants with higher SBP at baseline showed a greater response to hibiscus treatment (r = −0.421 for SBP change; P = 0.010). 3
These results suggest daily consumption of hibiscus tea, in an amount readily incorporated into the diet, lowers BP in pre- and mildly hypertensive adults and may prove an effective component of the dietary changes recommended for people with these conditions.
Previous studies have demonstrated that Hibiscus sabdariffa extracts reduce blood pressure in humans, this study from 2010 demonstrated that this effect is due to angiotensin converting enzyme (ACE) inhibitor activity. The aim of the current study was to isolate and characterizer the constituents responsible of the ACE activity of the aqueous extract of H. sabdariffa. Bioassay-guided fractionation of the aqueous extract of dried calyces of H. sabdariffa using preparative reversed-phase HPLC, and the in vitro ACE Inhibition assay, as biological monitor model, were used for the isolation. The isolated compounds were characterized by spectroscopic methods. The anthocyanins delphinidin-3-O-sambubioside (1) and cyanidin-3-O-sambubioside (2) were isolated by bioassay-guided purification. These compounds showed IC(50) values (84.5 and 68.4mug/mL, respectively), which are similar to those obtained by related flavonoid glycosides. 4 Researchers in this study did not find that Roselle was not as strong an ACE inhibitor as pharmaceutical reference drugs.
In this study from 2004, researchers compared the antihypertensive effectiveness and tolerability of a standardized extract from Hibiscus sabdariffa with captopril, a controlled and randomized clinical trial was done. Patients from 30 to 80 years old with diagnosed hypertension and without antihypertensive treatment for at least 1 month before were included. The experimental procedure consisted of the administration of an infusion prepared with 10 g of dry calyx from H. sabdariffa on 0.51 water (9.6 mg anthocyanins content), daily before breakfast, or captopril 25 mg twice a day, for 4 weeks. The outcome variables were tolerability, therapeutic effectiveness (diastolic reduction > or = 10 mm Hg) and, in the experimental group, urinary electrolytes modification.
The results showed that H. sabdariffa was able to decrease the systolic blood pressure (BP) from 139.05 to 123.73mm Hg (ANOVA p < 0.03) and the diastolic BP from 90.81 to 79.52mm Hg (ANOVA p < 0.06). At the end of the study, there were no significant differences between the BP detected in both treatment groups (ANOVA p > 0.25). 5
This study from 2009 compared the antihypertensive effectiveness of sour tea (ST; Hibiscus sabdariffa) with black tea (BT) infusion in diabetic patients.
Sixty diabetic patients with mild hypertension, without taking antihypertensive or antihyperlipidaemic medicines, were recruited in the study. The patients were randomly allocated to the ST and BT groups and instructed to drink ST and BT infusions two times a day for 1 month. Their blood pressure (BP) was measured on days 0, 15 and 30 of the study. The mean of systolic BP (SBP) in the ST group decreased from 134.4+/-11.8 mm Hg at the beginning of the study to 112.7+/-5.7 mm Hg after 1 month (P-value <0.001), whereas this measure changed from 118.6+/-14.9 to 127.3+/-8.7 mm Hg (P-value=0.002) in the BT group during the same period. The intervention had no statistically significant effect on the mean of diastolic BP (DBP) in either the ST or BT group. The mean pulse pressure (PP) of the patients in the ST group decreased from 52.2+/-12.2 to 34.5+/-9.3 mm Hg (P-value <0.001) during the study, whereas in the BT group, it increased from 41.9+/-11.7 to 47.3+/-9.6 mm Hg (P-value=0.01). In conclusion, consuming ST infusion had positive effects on BP in type II diabetic patients with mild hypertension. 6
This study from 2012 investigated the effect of the water extract of the dried calyx of HS and Hibiscus anthocyanins (HAs) on left ventricular myocardial capillary length and surface area in spontaneously hypertensive rats (SHRs). Twelve-week-old male SHRs were divided into eight groups (six rats in each group). Three groups were given three doses; 10%, 15% and 20% of the water extract of HS in lieu of drinking water for 10 consecutive weeks (HS10, HS15 and HS20) with one group kept as control (C). Another three groups were given three doses of the HAs orally at doses of 50, 100 and 200 mg/kg for five consecutive days with one group kept as a control (C). Systolic (SBP) and diastolic (DBP) blood pressures, as well as heart rate (HR), were measured weekly. After the experimental protocols, the left ventricles (LV) of all rats were obtained. Capillary surface area density and length density were determined by unbiased sterological methods on 3 μm LV tissue samples from perfusion-fixed hearts. HS ingestion significantly reduced SBP, DBP and LV mass in a dose-dependent fashion but did not affect the HR. HS significantly increased surface area and length density of myocardial capillaries by 59%, 65% and 86%, and length density by 57%, 77% and 57%, respectively. Myocyte nuclear volume was significantly decreased in HS-treated rats. There was a decrease (although insignificant) in SBP and DBP with HA ingestion compared with controls. These changes suggest that the observed beneficial effect of HS on high BP in SHRs could be mediated through a reduction in the diffusion distance between capillaries and myocytes, as well as new vessel formation. 7
A published paper from January 2010 concluded that there is insufficient clinical evidence that Roselle can control and lower blood pressure.
The Cochrane Database of Systematic Reviews published an meta-analysis in which they searched for evidence from clinical studies to evaluate the effectiveness of red tea compared with placebo or no treatment in hypertensive patients. They found that there is a lack of evidence from randomised control trials to demonstrate a benefit of Roselle tea in reducing blood pressure. They concluded that rigorous studies need to be done in order to answer this question. 8