Sources and Additional Links

Ajay, M., Chai, H.J., Mustafa, A.M., Gilani, A.H., Mustafa, M.R. (2007). Mechanisms of the anti-hypertensive effect of Hibiscus sabdariffa L. calyces. Journal of Ethnopharmacology, 109, 388-393.

Fakeye, T.O., Adegoke, A.O., Omoyeni, O.C., & Famakinde, A.A. (2007). Effects of water extract of Hibiscus sabdariffa, Linn (Malvaceae) “Roselle” on excretion of diclofenac formulation. Phytotherapy Research, 21, 96-98.

Herrera-Arellano, A., Miranda-Sanchez, J., Avila-Castro, P, Herrera-Alvarez, S., Jimenez-Ferrer, J.E., Zamilpa, A., … Tortoriello, J. (2007). Clinical effects produced by a standardized herbal medicinal product of Hibiscus sabdariffa on patients with hypertension. A randomized, double-blind, lisinopril-controlled clinical trial. Planta Medica, 73, 6-12. 

McKay, D.L, Chen, C.-Y. O., Saltzman, E., & Blumberg, J.B. (2010). Hibiscus sabdariffa L. tea (tisane) lowers blood pressure in prehypertensive and mildly hypertensive adults. The Journal of Nutrition, 140(2), 298-303.

Morton, J.F. (1987). Fruits of warm climates. Florida: Florida Flair Books.

Mozaffari-Khosravi, H., Jalali-Khanabadi, B.-A., Afkhami-Ardekani, M., Fatehi, F., Noor-Shadkam, M. (2009).The effects of sour tea (Hibiscus sabdariffa) on hypertension in patients with type II diabetes. Journal of Human Hypertension, 23, 48-54.

Nivsarkar, M., Patel, M., Padh, H., Bapu, C., & Shrivastava, N. (2005). Blastocyst implantation failure in mice due to “nonreceptive endometrium”: endometrial alterations by Hibiscus rosa-sinensis leaf extract. Contraception, 71, 227-230.

Ojeda, D., Jimenez-Ferrer, E., Zamilpa, A., Herrera-Arellano, A., Tortoriello, J., & Alvarez, L. (2010). Inhibition of angiotensin converting enzyme (ACE) activity by the anthocyanins delphinidin- and cyanidin-3-O-sambubiosides from Hibiscus sabdariffa. Journal of Ethnopharmacology, 127, 7-10.

roselle. (2010). In Encyclopædia Britannica. Retrieved November 28, 2010, from Encyclopædia Britannica Online: http://www.britannica.com/EBchecked/topic/509866/roselle 

Wahabi, H.A., Alansary, L.A., Al-Sabban, A.H., & Glasziuo, P. (2010). The effectiveness of Hibiscus sabdariffa in the treatment of hypertension: A systematic review. Phytomedicine, 17, 83-86.

Additional Links

Registered dietician discusses effects of Hibiscus tea on hypertension:

http://www.youtube.com/watch?v=Upd_5YyoNeM

Dr. Diane L. McKay discusses the results of her study:

http://www.youtube.com/watch?v=Wts2HHW1AdM

Adverse Effects/ Cautions/ Drug Interactions

Source: http://www.americanretiredseniors.com/wp-content/uploads/affordable_health_care.jpg

Before increased consumption of Hibiscus tea is recommended, researchers should investigate its potential adverse effects on female fertility. Nivsarkar et al. (2005) found that consumption of a water extract of the leaves of Hibiscus rosa-sinensis (a related species) led to the failure of blastocyst implantation in mice, possibly by interfering with uterine estrogen utilisation and therefore altering the physiology of the endometrium to make it “nonreceptive”.

In addition, it would be prudent to explore possible interactions that could occur between the chemical constituents of roselle and other drugs people are taking. Fakeye et al. (2007) found that patients who took diclofenac, an anti-inflammatory drug, together with with a Hibiscus sabdariffa beverage exhibited a reduced excretion of the drug in their urine on average compared to those who took the drug with water. This finding indicates that H. sabdariffa could have an impact on drug metabolism. Drug interactions of this nature would be particularly worrisome for drugs with a narrow therapeutic window for effectiveness and safety (Fakeye et al., 2007).

Current Use and What the Science Says

In addition to being an important component of commercially-marketed herbal tea blends (McKay et al., 2010), roselle is still used for its traditional medicinal properties, as well as for culinary purposes, in many countries around the world (Ojeda et al., 2010). Researchers are interested in exploring the anti-hypertensive properties of this plant, considering that a herbal tea remedy could be easily integrated into the diets of people with high blood pressure, especially in countries where Hibiscus tea is already consumed traditionally (McKay et al., 2010). 

A randomized controlled trial (RCT) was designed by McKay et al. (2010) to study the effects of Hibiscus tea on blood pressure in pre- and mildly-hypertensive adults. Participants in the experimental group received three servings of H. sabdariffa tea each day for six weeks, while members of the control group were provided with a beverage designed to mimic the real tea using food colouring and artificial flavours. The systolic and diastolic blood pressure of the participants was measured at baseline and once each week using an automated device. After six weeks, the decline in systolic blood pressure was significantly lower in the experimental group than in the control group (-7.2 ± 11.4 vs. -1.3 ± 10.0 mmHg; P=0.030). The decline in the experimental group’s diastolic blood pressure was also lower than that of the control group (-3.1 ± 7.0 vs. -0.5 ± 7.5 mmHg; P=0.160), but the difference was not significant.

Source: http://www.itechnews.net/wp-content/uploads/2008/12/usb-blood-pressure-monitor.jpg

Some of the strengths of this study were that it was double-blinded, and that it actually used a true placebo, rather than using black tea or a hypotensive drug for the ‘control’ group. The use of a standardized and automated method for measuring blood pressure, rather than having it measured manually by a physician, was also commendable. Weaknesses of the study included the sample size (n=66) and the fact that the active components of the tea were not isolated, suggesting that each tea bag could have contained a different quantity of anthocyanins, even if each one contained exactly 1.25g of dried calyces.

Herrera-Arellano et al. (2007) also conducted a double-blinded RCT to investigate the anti-hypertensive effects of H. sabdariffa on adults with existing stage 1 or 2 hypertension. The experimental group drank 250 mg of anthocyanins isolated from dried calyces dissolved in 250 mL of water every day for four weeks, while the control group was given 10 mg of the angiotensin converting enzyme (ACE) inhibitor lisinopril mixed with artificial flavour and colour. The blood pressure reduction in the H. sabdariffa group was 17.14/11.97 mmHg, which was less than that of the lisinopril group (23.31/15.39 mmHg; P<0.001). This study had a larger sample size (n=193), but 12% of participants were excluded from analysis due to non-adherence, which makes one question the validity of the results (Wahabi, Alansary, Al-Sabban, & Glasziuo, 2010). The main weakness of this trial was the lack of a true control.

Overall, it seems that there is reasonable evidence, based mostly on the results of the study by McKay et al. (2010), that the calyces of H. sabdariffa contain anti-hypertensive compounds, and that daily consumption of tea containing these compounds may lower blood pressure in adults with mild hypertension. However, further studies should be done with a larger sample size, H. sabdariffa extracts with standardized amounts of anthocyanins, and a true control group.

Active Components and Preparation

In many parts of the world the calyces of H. Sabdariffa are used to make hot and cold beverages (Mozaffari-Khosravi et al., 2009). Today, the plant is one of the most common ingredients in many herbal tea blends sold in the United States (McKay, Chen, Saltzman, & Blumberg, 2010). While the hypertension study by McKay et al. (2010) provided participants with Hibiscus tea prepared from 1.25g of ground, dried calyces, Herrera-Arellano et al. (2007) prepared a standardized amount (250 mg) of anthocyanins from dried calyces, which was then dissolved in 250 mL of water. The anthocyanins delphinidin 3-sambubioside and cyanidin 3-sambubioside, which are both flavonoid pigments, were suggested as the active constituents contributing to the anti-hypertensive effects of H. Sabdariffa in the two studies above (Herrera-Arellano et al., 2007; McKay et al., 2010). The plant contains many other chemical components, including alkaloids, β –carotene, citric acid, pectin, and stearic acid (Mozaffari-Khosravi et al., 2009).

Basic structure of anthocyanins. Source: http://www.mobot.org/mobot/research/apweb/top/chemicals/anthocyanin_base.gif

History/Traditional Use

Hibiscus sabdariffa, also known as roselle, has long been used for the treatment of hypertension by practitioners of traditional medicine around the world (Ajay et al., 2007; Mozaffari-Khosravi et al., 2009; Ojeda et al., 2010). Roselle, which belongs to the family Malvaceae, is used to treat a variety of health problems by people in Africa, South East Asia, and Central America (Ojeda et al., 2010). The plant, which is thought to be native to West Africa, was present in the West Indies by the early 16^th century and in Asia by the 17^th century (Encyclopædia Britannica, 2010). For the purposes of lowering blood pressure, it has usually been administered in the form of a tea made from the edible external portion of its flower (the calyx) (Encyclopædia Britannica, 2010). However, various traditional medicine remedies around the world call for the leaves, seeds, and root of the plant, in addition to the calyces (Morton, 1987, p.281-286).

Hibiscus sabdariffa. Source: http://ahmadalikarim.files.wordpress.com/2008/11/roselle-mama.jpg

In Mexico, where roselle is known as “jamaica” or “flor de jamaica”, it has been used as a diuretic, and for the treatment of fever, liver diseases, hypercholesterolemia, gastrointestinal disorders, and hypertension in the indigenous system of medicine (Ojeda et al., 2010). In East Africa, Hibiscus tea, which is known as “Sudan tea” in that region, is also taken to relieve coughs (Morton, 1987, p.281-286). Interestingly, roselle has even been used to reduce the after-effects of drunkenness in Guatemala (Morton, 1987, p.281-286).