HerbalEGram: Volume 17, Issue 8, August 2020

Editor’s note: Every other month, HerbalEGram highlights a conventional food and briefly explores its history, traditional uses, nutritional profile, and modern medical research. We also feature a nutritious recipe for an easy-to-prepare dish with each article to encourage readers to experience the extensive benefits of these whole foods. With this series, we hope our readers will gain a new appreciation for the foods they see at the grocery store and frequently include in their diets. We would like to acknowledge ABC Chief Science Officer Stefan Gafner, PhD, and HerbalGram Associate Editor Hannah Bauman for their contributions to this project.

By Jenny Perez, ABC Education Coordinator

Overview

The genus Hibiscus contains more than 300 species of annual and perennial herbaceous plants, woody shrubs, and small trees in Malvaceae, the mallow family.^1,2 Also known as rosemallows, Hibiscus species include roselle (H. sabdariffa), rose of Sharon (H. syriacus), and Chinese hibiscus (H. rosa-sinensis). The species most commonly used for food and medicine is roselle, which will be referred to as “hibiscus” in this article.³

In addition to roselle, other common names for hibiscus in English-speaking regions are sorrel, Jamaican sorrel, Indian sorrel, Queensland jelly plant, jelly okra, and Florida cranberry.^1,4 In French, hibiscus is called oseille de Guinée; in Spanish, flor de Jamaica; and in North Africa and the Middle East, it is known as karkadé, the name also used in pharmaceutical and food flavoring trade in Europe.^4,5

Hibiscus sabdariffa is an annual, herbaceous shrub native to Africa and widely distributed in the tropics and subtropics.^4-6 There are two main varieties: H. sabdariffa var. altissima and H. sabdariffa var. sabdariffa. The altissima variety is nearly branchless and considered an economically important textile plant that is grown for its fiber in India, the East Indies, Nigeria, and South America.^1,4,7 The sabdariffa variety is grown for its red calyces (the outermost parts of flowers) and used in food, herbal teas, and body care. The calyx, stems, and leaves are rich in organic acids, and their flavor resembles that of cranberry (Vaccinium macrocarpon, Ericaceae).⁴ There are more than 100 cultivars or seed varieties of H. sabdariffa. The major commercial varieties are grown in China, Thailand, Mexico, and Africa, specifically in Sudan, Senegal, and Mali.⁵

Hibiscus plants can grow up to seven feet tall and have sturdy, red-tinged stems and alternate, palmately-lobed leaves that are three to five inches long with reddish veins.^3,4,8 Hibiscus flowers are produced in the leaf axils and are bell-shaped, up to five-inches wide, white to pale yellow with a rose or maroon eye, with stamens fused onto a tubular structure surrounding the style.^1,3,6,8 Requiring four to six months to mature, hibiscus is a photoperiodic plant, producing flowers in fall as the day length steadily decreases.⁹ After pollination, the flower petals fall off, and the bright red calyces swell, growing to 1 ¼ to 2 ¼ inches in length. The fused calyx consists of five large sepals with a collar (known as the epicalyx) of eight to 12 narrow, pointed bracts around the base or receptacle of the flower.^1,4 The calyx fully encloses the velvety seed capsule and is vibrantly red, waxy, and plump.^1,4

Commercially known as “hibiscus flowers,” the calyx and epicalyx are typically harvested when vividly red and plump, before the seed pod matures and dries.^4,6,9 Hibiscus has indeterminate flower production; therefore, harvesting encourages more flower buds and calyces to develop.⁹ When seed capsules are mature, they turn brown and split open. Hibiscus seeds are light-brown, kidney-shaped, and 1/8 to 3/16 inches long with a slightly downy coat.^1,4

Historical and Commercial Uses

All the above-ground parts of the hibiscus plant, including the stem, leaves, calyces, and seeds, are used for food, fiber, or medicine.⁸ From its native origin in Africa, hibiscus began its journey as a cultivated food plant in the 17th century in Brazil. In 1707, cultivation began in Jamaica. In 1840, hibiscus was being cultivated in Guatemala, and by 1899, dried hibiscus calyces were a common item in the markets of Guadalajara, Mexico.⁴ In 1892, roselle jam was popular in Queensland, Australia, and briefly exported to Europe. By the early 1900s, hibiscus cultivation reached Hawaii and Puerto Rico. Seeds are thought to have been brought to North America by enslaved Africans. In the early 1890s, hibiscus cultivation began in Florida and fresh calyces were sold in markets as a southern substitute for cranberry.

The use of hibiscus leaves as a vegetable was first recorded in Java in 1687. The young leaves and tender stems are eaten raw in salads or cooked as a tangy condiment that can be eaten alone, with other vegetables in soups and sauces, or with meat or fish.^1,4,5,8,10 In African folk medicine, hibiscus leaves are used extensively as an emollient or antimicrobial topical remedy. In India, warmed leaves are used to soothe external wounds and abscesses.^2,11,12 Lotion made from the leaves is used on sores and wounds.⁴ Leaves are also used for animal fodder and fiber.^1,5

Hibiscus seeds are nutrient dense and widely consumed in many African countries.^1,2 The seed contains as much as 32% protein, which is reduced to 20-25% due to milling processes used to make seed flour. The seed also is high in the amino acids arginine, lysine, leucine, and glutamic acid.⁷ Hibiscus seeds contain 70% polyunsaturated fatty acids, primarily oleic and linoleic acid, and have a 1:2 ratio of saturated to unsaturated fatty acids. Additionally, hibiscus seeds contain 39-42% dietary fiber.⁷ The oil extracted from pressing the seeds is used as cooking oil known as mesta oil in China and West Africa.¹³ After oil extraction, the seeds can be roasted and brewed like coffee (Coffea arabica, Rubiaceae) beans or ground up and added to soups and salads.⁹

Traditionally, hibiscus seeds were also used as medicines. A hibiscus seed decoction is used in Nigeria to induce lactation postpartum. In India, seed decoctions are used to treat indigestion, relieve painful urination, and for general debility.^2,4,7,13

Since 1899, the hibiscus plant has been used primarily for the cooling beverage made from the calyces in the West Indies and in tropical climates in the Americas.⁴ In Egypt, “roselle-ade” is consumed cold in the summer and hot in the winter. In Jamaica, a traditional Christmas drink is prepared by steeping hibiscus calyces in an earthenware jug with grated ginger (Zingiber officinale, Zingiberaceae) and sugar (Saccharum officinarum, Poaceae) overnight, straining off liquid and serving it over ice (often with a dash of rum).^4,5

The mild fruity flavor and festive color of hibiscus calyces are used to add flavor and color to salads, jams, sauces, and teas. In Africa, fresh hibiscus calyces are cooked as a side dish and eaten with pulverized peanuts (Arachis hypogaea, Fabaceae).^5,8 In Mexico and Spain, sweetened hibiscus tea is known as Jamaican water or agua de Jamaica.^3,8 When enjoyed without sweetener, hibiscus tea can be used alone or in tea blends as a caffeine-free, tangy ingredient with nutritive and natural diuretic effects.^3,6

Hibiscus sauces and syrups are added to desserts and salad dressings.^5,9 The calyces contain an array of organic acids and a high pectin content (3.2%), which makes them ideal for jellies and jams.⁴ In Pakistan, hibiscus is a source of pectin for the fruit-preserving industry.^4,5,8

Hibiscus calyces are used as a traditional herbal medicine in India, Africa, the Middle East, Mexico, and Guatemala. Teas made from calyces have a history of use as a diuretic, to stimulate bile production, and reduce fevers, blood pressure, and blood viscosity.^2,4 Hibiscus tea is considered to be thirst quenching and is a favorite hangover remedy in Guatemala, as it is believed that hibiscus may reduce the rate of alcohol absorption. In eastern Africa, a hibiscus calyx infusion known as “Sudan tea” is consumed to relieve coughs.⁴ In Iran, sour hibiscus tea is a traditional treatment for hypertension.

In 1990, the German Commission E evaluated various European uses of hibiscus calyces and determined that efficacy for the claimed uses was not substantiated, including as a remedy to stimulate appetite, for colds, to dissolve phlegm, as a gentle laxative, diuretic, and for circulatory disorders.¹² Regardless, hibiscus is still used in many medicinal herbal products in German-speaking countries. It is used commonly used in in medicinal tea blends in combination with lemon balm (Melissa officinalis, Lamiaceae) leaf and St. John’s wort (Hypericum perforatum, Hypericaceae) herb for nervous restlessness and difficulty falling asleep.

When exported commercially from Africa, dried hibiscus calyces are pressed into solid cakes or formed into balls.⁷ Hibiscus calyces are hand-harvested, dried, and sold whole for the herbal tea and beverage industry.⁵ In Europe and the United States, dried hibiscus extracts are permitted for use in alcoholic beverages.^4,5

Over the past few decades, demand for hibiscus has been on the rise, resulting in an average of 15,000 metric tons exported annually for international trade.⁵ The main producers of hibiscus calyces are Sudan, Egypt, Mexico, India, Thailand, and China.^2,6 Germany and the United States are the main importers of hibiscus products. The fifth edition of the European Pharmacopoeia contains an official quality control standards monograph for whole or cut calyces and epicalyces collected during fruiting, under the European common name roselle (Hibisci sabdariffae flos).¹²

Sudanese hibiscus, formerly the primary source of hibiscus sold in herbal teas in the United States, is considered by many in the herb trade as the preferred product.¹² Due to the US trade embargo on agricultural goods from Sudan due to the conflict in Darfur, Sudanese hibiscus is now sold through brokers in Germany at a substantial price mark-up. Therefore, the majority of hibiscus in the United States now comes from China and Thailand.

Nutrients and Phytochemicals

Herbal beverages are sources of nutrients and phytochemicals that may play a role in preventing chronic diseases. Hibiscus tea is a caffeine-free functional food/beverage with potential therapeutic effects, specifically for the cardiovascular system. Hibiscus calyces contain ascorbic acid (vitamin C), thiamin (B₁), riboflavin (B₂), niacin (B₃), and beta-carotene (a precursor to vitamin A), as well as calcium, magnesium, potassium, sodium, iron, and zinc.^4,14,15

The primary therapeutic bioactive compounds in hibiscus calyces are polysaccharides, organic acids, phenolic acids, and flavonoids, mainly anthocyanins.^2,8 Evident by the tea’s vivid color, the anthocyanin content of hibiscus calyces is directly linked to its antioxidant, anti-inflammatory, and lipid-regulating effects.⁸ Delphinidin-3-O-glucoside accounts for 85% of hibiscus’ total anthocyanin content and has the most potent antioxidant capacity.

Hibiscus seeds are a source of high-quality protein, as determined by a food’s nutrient content and digestibility, and comparatively low amount of antinutrients like tannins.⁷ Hibiscus seed flour contains more methionine than soybean (Glycine max, Fabaceae) and grains and a low ratio of lysine to arginine, both of which are associated with heart health benefits, including a reduced risk of atherosclerosis. The high protein content and dietary fiber in hibiscus seeds also offer cholesterol-lowering benefits. Seed oil provides a concentrated energy source that is high in linoleic, oleic, and palmitic acids.^1,13 Defatted seed cakes, the solids that remain after oil pressing, still contain calories and nutrients and are an important regional source of food for people and livestock.⁷

Compared to the calyx, the leaves of hibiscus are abundantly produced and underutilized.¹⁰ Like the calyces, hibiscus leaves contain flavonoids and organic acids. Studies indicate that hibiscus leaves have antioxidant, cholesterol-lowering, and arterial plaque-reducing properties. The main phytochemicals found in hibiscus leaves are flavonoids and phenolic acids, which are associated with antioxidant capacity and anti-inflammatory activity.

Table 1. Phytochemicals Present in Hibiscus sabdariffa

Modern Research and Potential Health Benefits

Historically, hibiscus tea was used to treat inflammatory and cardiovascular diseases.¹⁵ In recent years, clinical trials on the use of hibiscus extracts have focused on high blood pressure (hypertension) and dyslipidemia. Dyslipidemia, which is characterized by high total cholesterol (TC) and low-density lipoprotein (LDL) cholesterol and low high-density lipoprotein (HDL) cholesterol, is associated with an elevated risk of atherosclerosis, cardiovascular disease, diabetes, obesity, and nonalcoholic fatty liver disease (NAFLD). Evidence suggests that daily consumption of hibiscus tea may significantly reduce blood pressure and normalize blood lipids in adults with metabolic syndrome, type 2 diabetes, and prehypertension to moderate hypertension.¹⁶

Cardioprotective Effects

Approximately 900 million patients throughout the world suffer from hypertension, a chronic medical condition in which the arterial blood pressure of the heart is elevated.^8,17 In clinical trials, daily consumption of hibiscus tea or hibiscus extract (standardized to 9.6 mg anthocyanins/dose) produced from calyces significantly lowered systolic and diastolic blood pressure in adults with type 2 diabetes and prehypertension (slightly elevated blood pressure) to moderate hypertension.^8,16,17

Studies on the antihypertensive effects of hibiscus extracts have demonstrated that hibiscus is a safe, effective, well-tolerated treatment option for mild to moderate hypertension.⁸ In a clinical trial conducted by Herrera-Arellano et al (2004), daily use of hibiscus tea (10 g of dried hibiscus calyces steeped for 10 minutes in 500 mL of water) was as effective at lowering blood pressure as captropril (50 mg/day), a commonly used ACE-inhibiting blood pressure medication.¹⁸ However, in a subsequent study by Herrera-Arellano et al (2007), a daily dose of 250 mg hibiscus anthocyanins was found to be less effective than 10 mg/day of lisinopril, another ACE inhibitor.¹⁷ In a separate clinical trial by McKay et al (2010), hibiscus tea was well tolerated by patients with prehypertension or mild hypertension, and there were no reported side effects.²⁰

The antihypertensive effects of hibiscus appear to be dose-dependent and are associated with the ACE-inhibitory activity of anthocyanins in the calyx, which prevents vasoconstriction and thus increases blood pressure.^8,14,16 Additionally, anthocyanins can decrease blood viscosity through cyclooxygenase inhibition,¹⁶ and polyphenols relax the smooth muscle cells in the blood vessel linings, both of which help reduce blood pressure.⁸ Research supports hibiscus as an effective potassium-sparing diuretic¹⁷ and ACE-inhibitor, which are properties shared by pharmaceutical medications commonly prescribed for hypertension.¹⁹ Additionally, hibiscus has cholesterol-lowering and anti-atherosclerotic effects.

Clinical evidence indicates that concentrated hibiscus beverages significantly lower blood pressure in diabetic, hypertensive patients compared with black tea (Camellia sinensis, Theaceae) and can offer similar benefits as common blood pressure lowering drugs.²⁰

A meta-analysis and systematic review of nine clinical trials that used hibiscus to improve cardiovascular disease risk factors indicated that consuming 1 g of standardized extract or 500 mL of hibiscus tea daily had a favorable effect on reducing TC and LDL cholesterol but had no effect on triglyceride (TG) levels.¹⁵ HDL cholesterol levels were also reduced, which is not a desirable effect, given its role in vascular protection. Additional research is needed to evaluate hibiscus tea’s ability to reduce TC, LDL, and protective HDL levels.

Metabolic Effects

Metabolic syndrome is associated with high blood glucose, obesity, high blood pressure, and high cholesterol. It is considered a pre-diabetic condition and can lead to cardiovascular disease.¹⁴ The use of metabolic drugs or natural dietary products (especially polyphenol-based) holds promise in addressing obesity in the long term and with fewer side effects.²¹ In a study on patients with metabolic syndrome, those receiving a daily dose of 3 g hibiscus standardized extract (standardized to 9.6 mg anthocyanins) experienced statistically significant reductions in blood glucose, TC, and LDL cholesterol levels.^2,17 Results from clinical trials on treating dyslipidemia with hibiscus have been positive overall. Typical doses used to reduce cholesterol are 1,000 mg dried herb three times daily; eight ounces hibiscus tea twice daily; or 100 mg standardized extract twice daily.¹¹

Studies have confirmed that the organic acids, anthocyanins, flavonoids, and polysaccharides in hibiscus not only have cholesterol-lowering effects but also have metabolic-regulating effects, which may be useful for weight management.^8,15 These metabolic-regulating effects include the ability to regulate energy metabolism, oxidative stress, inflammatory pathways, transcription factors, hormones, peptides, digestive enzymes, and epigenetic modifications.²¹

Other Uses

Anemia is an iron deficiency disease characterized by low red blood cell (RBC) levels. The RBC carries and delivers oxygen to all cells in the body. Ascorbic acid is the best-known potent enhancer of iron absorption.²² It has also been demonstrated that other organic acids, such as citric, malic, and tartaric acids, have similar, though less significant, effects on enhancing iron absorption. Containing an abundance of ascorbic acid as well as iron, hibiscus has a long history of use in treating anemia.⁸. Excessive iron in the body is known to increase the risks of acquiring certain infections, including malaria.²² However, there has been no direct clinical evidence that the use of hibiscus improves the iron status of adults.

Hibiscus tea’s traditional use to lower fevers and reduce inflammation has been attributed to its ability to inhibit/modulate cytokine production.⁸ The diuretic effects of hibiscus tea, combined with its anti-inflammatory properties, have been successfully used to reduce the recurrence of urinary tract infections by 36% in long-term care facilities. More high-quality clinical trials are needed to further investigate the various ways hibiscus tea may be utilized therapeutically.

Consumer Considerations

Offering seasonal ornamental beauty and utility, hibiscus is a common garden plant in tropical and subtropical climates. Hibiscus is hardy in USDA zones 9-10 and is damaged by frosts or freezes.⁹ Hibiscus species are multipurpose crops that require minimal input while yielding value-added products, including beverages, foods, fiber, and cosmetics.¹³ It takes approximately 11 pounds of fresh hibiscus calyces to make one pound of dried product.⁵ Seed stock must be collected annually.⁴ Ecologically, the showy hibiscus flowers provide nectar to larger pollinators, such as hummingbirds. They are also food for many insects.³

Hibiscus calyces are hand-harvested and labor-intensive to process.⁵ When processing fresh hibiscus calyces, use a paring knife to make an incision around the tough base or receptacle of the calyx below the bracts and remove it with the seed capsule attached.⁴ To extend their shelf life, calyces can be stored frozen or dried in a glass container for at least one year. Dried calyces yield optimal color and best flavor when boiled (decocted) rather than steeped (infused).^4,5

Plants naturally accumulate elements from the soil, which can be both beneficial and detrimental. A study on mineral uptake of common herbs used in teas found that hibiscus tea contained the greatest amounts of elements, including aluminum.²³ Due to potential aluminum toxicity, hibiscus tea consumption should not exceed more than one liter daily by sensitive adults and should also not be consumed by pregnant women, children under six months of age, and individuals diagnosed with chronic kidney failure.

Since some Hibiscus species, and close relatives like cotton root bark (Gossypium herbaceum, Malvaceae), have a history of use as herbal abortifacients or contraceptives, ingestion of large amounts of food or herbal preparations made with the leaves or calyces, such as hibiscus jam, should be avoided by pregnant or nursing women.^1,3 Hibiscus tea may interact with conventional drugs, including nonsteroidal anti-inflammatory drugs (NSAIDs, e.g., acetaminophen) and diuretics (e.g., hydrochlorothiazide), and possibly increase side effects and toxicity or reduce therapeutic effect.^8,16 Additionally, individuals with low blood pressure may experience dizziness upon consuming too much hibiscus tea. More clinical studies are needed to determine the safe dose of hibiscus tea with concomitant use of other drugs.⁸ Studies indicate that hibiscus tea is safe when consumed short term (less than three months) and at low doses (< 1,000 mg/kg/day), without any adverse effect on liver or kidney function.^8,16

Nutrient Profile²⁴

Macronutrient Profile (Per 100g fresh hibiscus calyces)

49 calories
0.96 g protein
11.31 g carbohydrates
0.64 g fat

Micronutrient Profile (Per 100g fresh hibiscus calyces)

Excellent source of:

Dietary Fiber: 35.7 g (119% DV)

Very good source of:

Vitamin C: 12.9 mg (14% DV)
Calcium: 215 mg (16% DV)
Magnesium: 51 mg (12% DV)

Good source of:

Iron: 1.29 mg (7% DV)
Vitamin A: 287 IU (5% DV)

Also provides:

Potassium: 208 mg (4% DV)
Phosphorus: 37 mg (3% DV)
Riboflavin: 0.028 mg (2% DV)
Niacin: 0.31 mg (2% DV)
Thiamin: 0.011 mg (1% DV)

DV = Daily Value as established by the US Food and Drug Administration, based on a 2,000-calorie diet.

Image credits:

All photographs: Hibiscus sabdariffa calyces. ©2020 Steven Foster

References

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