Hypertension and diabetes often coexist; hypertension is twice as frequent in diabetic as in non-diabetic persons. Hypertension contributes significantly to the morbidity and mortality of diabetic persons and accounts for as much as 75% of the cardiovascular disease risk in this population. Although hypertension is more frequent in developed than in developing countries, its prevalence is rapidly increasing in many developing nations—particularly in Iran. Both animal and human studies have shown that extracts of hibiscus (Hibiscus sabdariffa, Malvaceae) calyces (outer coverings of the flower petals) beneficially affect lipid profiles and reduce hypertension. This is especially true of extracts standardized to total anthocyanins.^1,2 The mechanisms responsible for the blood pressure-lowering effect are not proven; however, the antioxidative and diuretic effects of hibiscus, which is also known as roselle and sour tea, are thought to be primarily responsible for its beneficial effects.

The objective of the present study was to compare the short-term effects of hibiscus tea with those of black tea (Camellia sinensis, Theaceae) on blood pressure in patients with type 2 diabetes. Sixty mildly hypertensive (systolic blood pressure [SBP] not >160 mm Hg and diastolic blood pressure [DBP] not >100 mm Hg) patients with type 2 diabetes (duration: >5 years) were enrolled in this double-blind, randomized, controlled trial, which was conducted at the Yazd Diabetes Research Center in Yazd, Iran.

The patients were randomly assigned to consume a glass of either hibiscus or black tea twice daily for 1 month. The hibiscus was imported from Saudi Arabia and the black tea from Sri Lanka. Each tea sachet weighed 2 g and was steeped in 240 ml of boiling water, to which 5 g of sugar was added, before ingestion. The subjects were prohibited from drinking any other tea during the study. SBP, DBP, and pulse pressure (PP) were measured on days 1, 15, and 30. Fifty-three patients (45 women and 8 men), 27 in the hibiscus group and 26 in the black tea group, completed the study.

At baseline, no significant differences in weight, age, or body mass index were observed between the 2 groups; however, significant differences in DBP (P = 0.01), SBP (P < 0.001), and PP (P = 0.003) were observed between groups. DBP did not change significantly during the study and did not differ significantly between groups at any time point. In contrast, SBP decreased significantly (P < 0.05) by 7.8% from baseline (134.4 ± 11.8 mm Hg) to day 15

(123.3 ± 10.9 mm Hg) and by 8.1% from day 15 to day 30 (112.7 ± 5.79 mm Hg) in the hibiscus group and increased significantly (P < 0.05) by 2.7% from baseline (118.6 ± 14.9 mm Hg) to day 15

(120.7 ± 13.6 mm Hg) and by 6.2% from day 15 to day 30 (127.3 ± 8.74 mm Hg) in the black tea group. Furthermore, SBP was significantly different between the hibiscus and black tea groups at baseline and on day 30 (P < 0.001). PP decreased significantly (P < 0.001) from baseline (52 ± 12.2 mm Hg) to day 15 (34.5 ±

9.3 mm Hg) in the hibiscus group and increased significantly (P = 0.01) from baseline (41.9 ± 11.7 mm Hg) to day 30 (47.3 ± 9.6 mm Hg) in the black tea group. PP was significantly different between the hibiscus and black tea groups at baseline (P = 0.003)

and day 30 (P < 0.001). The therapeutic effectiveness of the interventions (defined as a decrease of ≥10 mm Hg in the measured variables) over the 30-day study period was calculated as 48.1% in the hibiscus group and as 15.4% in the black tea group (P = 0.01). Compliance was 95% in the black tea group and 92% in the hibiscus group.

A significant positive therapeutic effect of hibiscus ingestion on blood pressure was observed in the diabetic patients in this study. The authors conclude that the present study “supports the results of similar studies in which antihypertensive effects have been shown” for hibiscus.

The safety of hibiscus as a widely consumed beverage is well established; previous short-term clinical trials measuring bloodpressure-lowering effects have not indicated any adverse effect. The authors note that the sustainability of effects on BP should be evaluated further. They also admit to 2 egregious shortcomings of their study, namely (1) the lack of a placebo control group and (2) the lack of monitoring of changes in blood chemicals such as sodium, potassium, and angiotensin converting enzyme (which causes an elevation of blood pressure).

References

1. Herrera-Arellano A, Flores-Romero S, Chavez-Soto MA, Tortoriello J. Effectiveness and tolerability of a standardized extract from Hibiscus sabdariffa in patients with mild to moderate hypertension: a controlled and randomized clinical trial Phytomed. 2004;11:375-382.

2. Herrera-Arellano A, Miranda-Sanchez J, Avila-Castro P, et al. Clinical effects produced by a standardized herbal medicinal product of Hibiscus sabdariffa on patients with hypertension. A randomized, double-blind, lisinopril-controlled trial. Planta Med. 2007;73:6-12.