James Odell, OMD, ND, LAc
Clove (Syzygium aromaticum)
Clove is a tropical evergreen tree of the family Myrtaceae, and its small reddish-brown flower buds are used as a spice. Clove buds possess an intense fragrance and burning taste. They have a deep brown color and a powerful fragrant odor that is warm, pungent, strongly sweet, and slightly astringent. Cloves were important in the earliest spice trade and are believed to be indigenous to Indonesia's Moluccas, or Spice Islands. The term ‘clove’ is derived from the French word ‘Clou’ and the English word ‘Clout’, both meaning ‘nail’- from the likeliness of the flower bud of the clove tree to a broad-headed nail.
Medicinal Benefits of Clove
Clove is one of the most valuable spices that has been used for centuries as a food preservative as well as for its many medicinal benefits. This plant represents one of the richest sources of phenolic compounds such as eugenol, eugenol acetate, and gallic acid and possesses great potential for pharmaceutical, cosmetic, food, and agricultural applications.
The US Food and Drug Administration has approved clove oil as an analgesic in dentistry, a flavoring additive in foods, and a fragrance component in personal care and aromatherapy products. The risk of food allergy from clove oil appears to be small.1
Health Benefits of Clove
Clove has physical, mental, and emotional health benefits. It possesses antioxidant, anti-fungal, anti-viral, antimicrobial, anti-diabetic, anti-inflammatory, antithrombotic, anesthetic, pain relieving and insect-repellent properties.2, 3
Description of Clove
The clove tree is an evergreen tree that grows to a height ranging from 8-12 meters (25 to 40 feet) in height, with large square leaves and sanguine flowers in numerous groups of terminal clusters. The flower buds are at first a pale color and gradually become green, after which they develop into a bright red when ready for collecting. Its gland-dotted leaves are small, simple, and opposite. The trees are usually propagated from seeds that are planted in shaded areas. Flowering begins about the fifth year; a tree may annually yield up to 34 kg (75 pounds) of dried buds. The buds are hand-picked in late summer and again in winter and are then sun-dried. Cloves vary in length from about 13 to 19 mm (0.5 to 0.75 inch).
History of Clove
Clove is one of the most ancient and valuable spices of the Orient, with its origin as old as the first century, before Christ. In India, it is used in almost all spicy dishes. It has been used as a spice and fragrance for more than 2,000 years in China. In traditional Chinese medicine, clove is known as ding xiang or “nail spice” and was used to treat among other things indigestion, nausea, vomiting, and infections.4 Chinese officials would chew cloves to freshen their breath before speaking to the emperor.
In the 4th Century AD cloves began to be traded internationally, making their way to Europe and other parts of Asia via the Silk Road and other trade routes. In Medieval Europe cloves were a prized spice for flavoring food. They were also used in medicine for their antiseptic and anti-inflammatory properties to treat conditions like dyspepsia, acute or chronic gastritis, and diarrhea.5, 6, 7, 8
In the 15th to 17th centuries Europeans, especially the Portuguese and Dutch, sought to control the clove trade. The spice was valued highly and was one of the reasons that led to the Age of Exploration. In the 17th century, the Dutch established a monopoly on the clove trade, going to the extreme of controlling and limiting the cultivation of cloves to one island, to keep prices high. British and French challenged the Dutch monopoly, leading to the cultivation of cloves in other parts of the world, like Zanzibar, which eventually became the world’s largest producer of cloves.
Modern Uses of Clove
Today cloves are grown in various countries around the world, including Indonesia, Madagascar, Tanzania, and Sri Lanka. They are used in cuisines globally, in the production of clove oil, and in traditional medicine for such diverse problems as coughs and colds, diarrhea, digestive disorders, diabetes, toothaches, memory loss, erectile dysfunction, and arthritis.9, 10
Culinary uses for clove include as a flavoring addition to meats, especially ham, stewed fruits, pickles, curries, pies, salads, and spiced alcoholic beverages such as whisky.
Clove is known to mask spoiled food smells by interfering with odor maps in the olfactory bulb of the forebrain.11 It also finds application in perfumes, oral products, soaps, and detergents. In Indonesia, cloves are added to tobacco in kreteks, which are aromatic high-tar cigarettes.
Clove cigarettes or kreteks are more potent than regular cigarettes in delivering carbon monoxide, tar, and nicotine. There are substantial health hazards associated with inhaling clove cigarette smoke, including severe lung injury in individuals with prodromal respiratory infections and aspiration pneumonitis in some individuals with normal respiratory tracts.12, 13, 14
Chemical Compounds Isolated from Clove
From clove species three essential oils are available: clove stem oil, clove bud oil, and clove-leaf oil. Each clove essential oil differs in chemical composition, flavor, and color. In cloves, the essential oil amounts of secondary metabolites are affected by the nature of the soil, climate, cultivation techniques, and genetic factors.15
Clove oil is reported to contain 75% to 90% eugenol, followed by β-caryophyllene and lesser amounts of α-humulene and eugenyl acetate.16, 17, 18
Eugenol, β-caryophyllene, and eugenol acetate are likely present in all types of samples, although the relative composition of components within an extract will vary considerably, depending on specific isolation protocols used by each investigator.
Ethanolic extracts contain eugenol, β-caryophyllene, and eugenol acetate as major components and possibly some flavonoids, tannins, and alkaloids.19, 20 Hexane extracts have been reported to contain eugenol, eugenol acetate, and β-caryophyllene, as well as flavonoids, phenols, saponins, alkaloids, and tannins.21, 22
Other phenolic acids found in clove are caffeic, ferulic, elagic, and salicylic acids. Flavonoids such as kaempferol, quercetin, and its derivates (glycosylated) are also found in clove in lower concentrations.
Another important compound found in the essential oil of clove in concentrations up to 2.1% is α-humulen. Other volatile compounds present in lower concentrations in clove essential oil are β-pinene, limonene, farnesol, benzaldehyde, 2-heptanone, and ethyl hexanoate. As well as triterpenoids like oleanolic acid, stigmasterol, and campesterol; and several sesquiterpenes. 23, 24
Water extracts can contain eugenol, trans-caryophyllene, anthraquinones, saponins, flavonoids, tannins, and eugenol derivatives.25
Bioavailability
The bioavailability and tissue distribution of eugenol and other clove components have been studied in animals, humans, and other organisms.26, 27, 28, 29, 30, 31, 32, 33, 34
In healthy male and female human volunteers, acute oral administration of eugenol is followed by rapid absorption in the digestive tract, evidence of a first-pass effect, and almost complete excretion in the urine within 24 hours.35, 36
Following an acute oral dose of 150 mg eugenol, amounts in the range of 0.02 to 100 µg/mL were detected in serum, urine, and bile. A serum concentration of 7 µg/mL (42.6 nM) was specifically reported.37
Eugenol levels in the blood of rats peak rapidly after repeated oral administration and exhibit a mean half-life in blood of 14.0 hours.38
Interestingly, eugenol and clove oil have been reported to improve the oral and percutaneous absorption and bioavailability of a variety of drugs.39, 40
Antioxidant Activity
As a spice, clove is a champion of all the plant antioxidants known to date. The Oxygen Radical Absorption Capacity (ORAC) test is a scale developed by the U.S. Department of Agriculture for comparing antioxidant activity. The ORAC score of ground clove is approximately 300,000. A drop of clove oil is 400 times more powerful as an antioxidant than wolfberries or blueberries.
Oral dosing of rats with eugenol (1000 mg/kg) for 15 and 90 days led to increased intestinal activity of glutathione-S-transferase, an enzyme that plays an important role in controlling oxidative stress in cells.41
Anti-inflammatory Properties of Clove
Eugenol, the primary component of clove’s volatile oils, functions as an anti-inflammatory agent. In animal studies, the addition of clove extract to diets already high in anti-inflammatory components (like cod liver oil, with its high ω-3 fatty acid content) brings a synergistic effect. Clove also contains a variety of flavonoids, including kaempferol, rhamnetin, and β-caryophyllene which also contribute to clove’s anti-inflammatory and antioxidant properties.
Extensive research has been conducted on clove and its constituents exhibit multiple actions in modulating inflammation and immune responses in vitro. Clove and eugenol were reported to inhibit cyclooxygenase 2 and nitric oxide synthase in a variety of cell lines, in part by modulating signaling pathways and by inhibiting oxygen radical generation and the production of proinflammatory mediators. 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62
Clove oil and eugenol have been shown to produce diverse immunomodulatory activities including anaphylaxis suppression, improved humoral- and cell-mediated immunity, and inhibition of immediate hypersensitivity.63, 64, 65, 66, 67, 68, 69, 70, 71
Eugenol is being developed as part of a prodrug to treat inflammation. When combined with aspirin into an aspirin-eugenol-ester compound, the adverse effects of each compound were reduced, and agent stabilization and overall therapeutic efficacy were enhanced.72
Antimicrobial Properties of Clove
Clove is known to possess antimicrobial properties and is thus used orally for infections as well as topically in toothpaste, mouthwashes, and throat sprays. The antimicrobial activities of clove have been proven against several bacterial and fungal strains. Clove exhibited antibacterial activity against gram-negative anaerobic periodontal pathogens, including Porphyromonas gingivalis, Prevotella intermedia, and stomach Helicobacter pylori.73, 74, 75
Clove exhibits antifungal activity against Candida albicans and Fusarium oxysporum as well as antiviral activity against Herpes Simplex virus (HSV) 1 and 2.76, 77
Clove has also been shown to be an effective antiparasitic to Trichinellosis (Trichinella spiralis).78 Trichinellosis is sometimes referred to as the "pork worm" due to it being typically encountered in undercooked pork products.
Anticancerous Properties
Clove has shown potential anticancer activity against colon, gastric, breast, prostate, and skin cancer, as well as melanoma and leukemia.79, 80, 81, 82, 83 Studies indicate the ethyl acetate extract of cloves displays antitumor activity both in vitro and in vivo.84 Clove extract may represent a novel therapeutic herb for cancer treatment, and its oleanolic acid is one of the components responsible for part of its antitumor activity.
Dental and Periodontal Properties
Periodontal diseases are multifactorial in nature and several risk and susceptibility factors have been proposed to explain the onset and progression of the diseases. Periodontal disease initiation and progression occur largely because of the host's response to the oral microbiome, its pH, and microorganisms present in dental biofilm.85
The pathogens stimulate the host response resulting in the release of harmful by-products such as cytokines and prostaglandins by leukocytes, fibroblasts, or other host tissue-derived cells and enzymes. These break down extracellular matrix components, such as collagen, as well as host cell membranes, consequently leading to periodontal attachment loss and bone resorption. Host modulation therapeutic strategies are aimed at balancing the commensal bacteria that assist in the inhibition of the progression of inflammatory bone loss associated with periodontitis.
Because clove displays antibacterial action against gram-negative anaerobic periodontal microorganisms, including Porphyromonas gingivalis and Prevotella intermedia it reduces these pathogenic microorganisms that affect the gums. 86, 87, 88
Besides its antimicrobial properties, clove’s anti-inflammatory and antioxidant properties reduce inflammation and oxidative stress in the gingiva.89, 90 It is shown that clove may reduce periodontal inflammation by modulation of the signaling pathway (NF-κB) and suppression of IL6, COX-2, and TNF-α.91, 92, 93, 94
Studies demonstrated that therapy with clove and its active components like eugenol can be beneficial for the treatment of periodontal disease as a natural antiplaque or anti-gingivitis agent. Clove can be effectively incorporated into therapeutic agents formulated against periodontal diseases in the form of mouthwashes and toothpaste.
How to Make Clove Oil
Buy fresh whole cloves.
Crush the cloves with a mortar and pestle.
Place your cloves in a small dark glass jar.
Cover the cloves with carrier oil – olive, jojoba, coconut
Seal the jar and shake it gently a couple of times.
Let the jar sit for about a week.
Strain the cloves out of the oil.
Summary
Clove has numerous pharmacological benefits as an antimicrobial, anti-inflammatory, hepatoprotective, anti-stress, and anesthetic. Clove has proved to be a good antioxidant as well. The single drop of its oil is many times stronger and more effective compared to other antioxidants like blueberries and wolfberries. It is found to be a very effective plant with many proven benefits having the least adverse effects. Its proven biological activities confirm why this plant has been employed treasured for centuries.
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