Traditionally, all parts of the hibiscus (Roselle; Hibiscus sabdariffa, Malvaceae) plant are used for medicine and food. The young leaves and stems are eaten raw. The seeds are boiled and eaten in soup. The calyces are frozen or sun-dried and eaten. The calyces/flowers are used worldwide in drinks, jams, jelly, sauces, and as a natural food colorant. In traditional medicine, hibiscus is used to treat colds, toothaches, urinary tract infections, hangovers, flatulence, diarrhea, dysentery, hypertension, liver disease, fever, and high cholesterol. According to the authors, this is the first review to focus on hibiscus calyces. The authors do not describe their method of assessing the literature. It is therefore not clear whether they are reporting on all available research or only research that they chose to discuss.
Hibiscus is cultivated until approximately three weeks to the onset of flowering. The calyces are rich in carbohydrates, fiber, protein, vitamins, minerals, and bioactive compounds. The bioactive compounds include flavonoids (mainly anthocyanins) and organic acids (mainly malic acid and citric acid). However, differences in extraction techniques and varieties of H. sabdariffa make comparing research a challenge.
Several in vivo studies demonstrate that extracts or ground calyces administered orally lower total cholesterol, triglyceride, and low-density lipoprotein cholesterol (LDL) in the serum; and reduce the body weight and obesity. Three studies evaluated the effect in humans. One study was a randomized, triple-masked, placebo-controlled study of patients (n = 72) treated with 6 g/day of hibiscus powder for four weeks and concluded that hibiscus significantly decreased total cholesterol, LDL, and triglyceride levels without any significant decrease in high-density lipoprotein cholesterol (HDL). In another study, patients with metabolic syndrome treated with 100 mg/day hibiscus extract for one month had a significant decrease in total cholesterol and glucose level and an increase in HDL. In the third randomized, controlled study, patients treated with 1000 mg hibiscus extract significantly reduced serum cholesterol. For all three studies, the P-values were not reported, and it is not clear if the difference was compared with placebo or baseline. The authors conclude that longer studies are needed. Also, all three studies used a different extract, so it is difficult to make conclusions about the antihyperlipidemic effect.
In vivo studies demonstrate that the aqueous hibiscus extract lowers blood pressure. Four studies evaluated the effect on humans. In patients (n = 54) with moderate hypertension, hibiscus tea for 12 days lowered blood pressure (dose not reported). In a randomized, double-blind, lisinopril-controlled clinical trial, patients with hypertension (n = 171) were treated with hibiscus extract for four weeks (dose not reported); hibiscus extract decreased blood pressure but was not as effective as 10 mg lisinopril. Another randomized, double-blind, placebo-controlled clinical trial involving patients with pre- or mild hypertension (n = 65) reported a decrease in blood pressure after drinking hibiscus tea (dose not reported). Another study of patients (n = not reported) with metabolic syndrome treated with 125 mg/kg/day polyphenolic hibiscus compounds for four weeks demonstrated that hypertension was managed (additional details not provided). The authors conclude that the test compounds were not standardized to an active component so the studies cannot be compared, and more randomized, double-blind, placebo-controlled clinical trials for a longer duration are needed.
In vivo studies demonstrate that hibiscus extract decreases inflammation thereby preventing early diabetic nephropathy, reduces hyperglycemia and hyperinsulinemia, decreases urinary tract infection, and decreases adenine-induced chronic kidney disease. One study demonstrated that “roselle drink” prevented urinary tract infection in residents with urinary catheters in long-term care facilities (no dosage reported). The authors conclude that hibiscus has the potential to help chronic inflammatory disease.
Twenty-five varieties of Mexican hibiscus extract were tested against gram-positive and gram-negative bacteria in vitro, and the extracts were more effective against gram-positive bacteria. The extract also had antifungal activity. The activity is attributed to the flavonoids. In vivo and clinical studies are needed.
Diuretic, Uricosuric, and Hyperuricemia Effect
In vivo studies demonstrate that hibiscus extract has diuretic effects and inhibits oxonic acid-induced hyperuricemia. However, the diuretic effects of hibiscus extract in humans are under debate. One study reported an increase in urinary volume and another study found no increase (no study details were provided). Additional studies are needed.
In vivo studies demonstrate that hibiscus extract significantly increased hematocrit and hemoglobin. In patients with mild to moderate anemia, 1000, 1500, or 2000 mL/day hibiscus aqueous extract for 30 days did not improve iron status. The authors conclude that the research is limited, and more well-designed studies are needed.
An in vivo study showed that a methanolic extract of hibiscus significantly reduced a biomarker of colon carcinogenesis. In another in vivo study, hibiscus anthocyanins inhibited the progression of leukemia. In vitro, delphinidin 3-sambubioside from hibiscus induced dose-dependent apoptosis in human promyelocytic leukemia cells. Also, studies using in vitro cell lines showed that hibiscus juice had anti-proliferative effects on breast, ovarian, and cervical cancer cells. The authors conclude that additional studies are needed.
Used Against Cadmium Poisoning
In vivo, hibiscus extract reduced hepatotoxicity induced by cadmium poisoning and protected rats against liver damage and testis lipoperoxidation.
In vivo, hibiscus extract reduced cisplatin-induced sperm abnormality, increased sperm motility, and increased testicular antioxidant enzymes. The authors conclude that hibiscus extract has the potential to be used as a fertility treatment. Clinical trials are needed.
Doses > 1000 mg/day may be associated with increased liver enzymes, urea, creatinine, and uric acid. Aqueous extract of hibiscus decreased the elimination of acetaminophen, diclofenac, and hydrochlorothiazide. In vitro studies evaluating the effect of hibiscus extract on a drug, metabolism concluded that there may not be a significant herb-drug interaction through cytochrome P450 enzymes. The authors conclude that more research on drug-herb interactions are needed and high doses of hibiscus could be toxic.
Dosing recommendations cannot be made, according to the authors. Hibiscus calyces contain bioactive compounds that may effectively treat a variety of diseases. It is safe at low doses. It can be used as a functional food or medicinal product. Research is needed to create a standardized fingerprint for quality control.