Montalvo-González E, Villagrán Z, González-Torres S, et al. Physiological effects and human health benefits of Hibiscus sabdariffa: A review of clinical trials. Pharmaceuticals (Basel). April 2022;15(4):464. doi:10.3390/ph15040464.

The World Health Organization declared that chronic non-communicable diseases are the main cause of death worldwide. These diseases include hyperglycemia, hyperlipidemia, hypercholesterolemia, diabetes mellitus type 2, hypertension, arteriosclerosis, cancer, and chronic lung illnesses. These diseases can affect people of all ages, with people living in middle- and low-income countries at a higher risk. Prevention and control of the diseases are crucial for the health of all populations. Risk factors associated with the diseases include elevated blood pressure, overweight, obesity, high glucose, and lipid blood levels. Hibiscus (Hibiscus sabdariffa, Malvaceae) is one herb that has many beneficial effects. It contains phenolic acids, flavonoids, anthocyanins, organic acids, and dietary fiber. Several studies have documented the ethnopharmacological efficacy of hibiscus for a range of effects. The authors conducted a narrative review to summarize the physiological effects and health benefits of hibiscus reported in clinical trials.

Hibiscus is used for non-medicinal and medicinal properties throughout the world and is readily available commercially. It is used in hot and cold drinks, tea, jellies, jams, sauces, wines, syrups, ice cream, and chutneys. Traditionally, it is prepared as a decoction, infusion, or maceration. Therapeutic properties include as an antimicrobial, antiparasitic, antioxidant, laxative, antispasmodic, diuretic, hepatoprotective, antianemic, anti-inflammatory, analgesic, antitussive, choleretic, antipyretic, hypotensive, cardioprotective, and neuroprotective agent. In vitro and in vivo studies have indicated hibiscus has antioxidant, antihypertensive, antidiabetic, vasorelaxant, cardioprotective, antibacterial, antiviral, antiproliferative, cytotoxic, neuroprotective, sedative, antianxiety, antidepressant, hepatoprotective, antihyperinsulinemic, anti-obesity, anti-inflammatory, antianemic, and anti-ulcer activities.

In clinical trials, hibiscus was found to prevent or control chronic non-communicable diseases through its antihypertensive, antidyslipidemic, hypoglycemic, antianemic, nephroprotective, antioxidant, anti-xerostomic, and anti-inflammatory properties and have an effect on body fat mass reduction.

In an observational study with one male patient with hypertension, it was found that a single dose of hibiscus tea reduced systolic and diastolic blood pressure. Similarly, an intervention study showed a beneficial effect for systolic and diastolic blood pressure in healthy patients. Over a dozen other randomized clinical trials and quasi-experimental studies also indicated positive effects on blood pressure; however, there was an inconsistency regarding the effects on systolic versus diastolic blood pressure.

Hibiscus was found to reduce total cholesterol and low-density lipoprotein and increase high-density lipoproteins in over six interventions and placebo-controlled trials; however, hibiscus did not show an effect on serum lipid levels in a number of other trials. There were more trials that had positive effect than no effect.

When taken with a high-carbohydrate breakfast, the intake of hibiscus appeared to slow the rise of blood glucose. In a quasi-experimental and control study, the consumption of hibiscus lowered fasting blood glucose levels; however, there was no improvement in postprandial blood glucose levels. Other studies indicated a reduction in the fasting blood glucose, fasting insulin levels, postprandial glucose, and cortisol levels, an improvement in insulin resistance, and a tendency for lower postprandial insulin response. Two studies, however, did not show any change in blood glucose levels.

Hibiscus indicated a reduction in weight and abdominal fat in a randomized clinical study of 36 patients with obesity. In another double-blind, placebo-controlled, and randomized study, hibiscus supplementation was associated with an increase in adiponectin levels. There was also a reduction in body weight, body mass index, and fat mass in another double-blind, placebo-controlled study.

In a study with patients with diabetic nephropathy, hibiscus supplementation improved renal function and reduced blood urea nitrogen, blood creatinine, urine creatinine, urine albumin, and high-sensitive C-reactive protein levels. Another study showed an increase in oxalate, citrate, and uric acid excretion levels after consuming hibiscus in patients who had renal stones; however, a different trial demonstrated no effect on renal stone formation. In a randomized, double-blind, lisinopril-controlled study, there was a decrease in sodium levels after consuming hibiscus; however, there was no difference in potassium. In a prospective randomized clinical-case control study, there was a decrease in creatinine and uric acid levels after consuming hibiscus for 28 days, and in a randomized phase three clinical study, there was a reduction in urinary tract infection symptoms after taking a hibiscus supplement for seven days.

In a study with patients with anemia, it was found that hibiscus exhibited hematopoietic effects. In healthy patients, there was an improvement in hematological parameters. Another study found the consumption of a hibiscus water drink increased hemoglobin levels; however, a different study indicated no effects on any hematocrit, platelet, and erythrocyte values.

The antioxidant effect was shown in multiple trials and interventions. The hibiscus intervention resulted in an increase in average antioxidant capacity in the blood samples. The trials found increased antioxidant activity, a decrease in malondialdehyde levels, an increase in ferric reducing antioxidant power and ascorbic acid levels, and an increase in urinary hippuric acid excretion. There was also an improvement in the activities of extracellular superoxide dismutase, glutathione peroxidase, glutathione-S-transferase, and total antioxidant capacity and ascorbic acid.

Other activities found in trials included a decrease in the production of monocyte chemoattractant protein-1, a reduction in the expression of interleukine-6 and interleukine-8, an improvement in dry mouth symptoms, an increase in saliva production, and a regulating effect on saliva pH.

The authors conclude that hibiscus has a beneficial effect on health. Trials have shown antihypertensive, hypoglycemic, lipid-lowering, antianemic, anti-inflammatory, antioxidant, anti-xerostomic, and diuretic effects. The authors also found numerous limitations in the included studies and recommend further large-scale trials with higher doses and follow-ups to verify study findings. The authors state no conflict of interest.

—Dani Hoots