Oregano

Origanum vulgare (of the family labiatae^[1]) is a spice and tea that is commonly referred to as oregano, with the essential oil derived from this plant referred to as oil of oregano. This plant is botanically related to another spice known as Marjoram (Origanum majorana) and is commonly called 'wild marjoram' due to this relationship.

It is traditionally used as a medicinal carminative and stomachic (taken with meals to reduce gastrointestinal distress, sometimes as a tea^[2]) as well as for diuretic and emmenagogue purposes.^[3] Other indications include analgesia and antiinflammation, such as for chronic rheumatism, toothache, and earache.^[3]

The dried leaves of origanum vulgare (excluding the essential oil component) contain:

• Rosmarinic acid^[4][3] at 123.22mg/g in the water extract (tea)^[5]
• Ursolic acid^[4][6] at 10.04mg/g dry leaf weight^[7]
• Oleanolic acid^[4][6] at 6.51mg/g dry leaf weight^[7]
• Caffeic acid^[3]
• 4'-O-beta-D-glucopyranosyl-3',4'-dihydroxybenzyl protocatechuate (Oreganol A^[6] estimated at 3.8mg/g dry weight^[8]) and the same glycoside for 4-O-methylprotocatechuate (Oreganol B^[8])
• Flavonoids eriocitrin (17.20 mg/g in the water extract^[5]), apigenin (5.97 mg/g of the 7-O-glucoside in the water extract, aglycone less than 0.03mg/g^[5]), luteolin (3.89mg/g of the 7-O-glucoside and 0.61mg/g of the aglycone in the water extract^[5]), chrysoeriol, diosmetin, quercetin (0.70mg/g in the water extract^[5]), and eriodictyol^[3]
• Cosmocide^[3]
• Vicenin-2^[3]
• p-menth-3-ene-1,2-diol 1-O-β-glucopyranoside^[3]
• Thymoquinol as 2-O-β-glucopyranoside, 5-O-β-glucopyranoside, and 2,5-O-β-diglucopyranoside^[3]
• 12-hydroxyjasmonic acid and its β-glucopyranoside^[3]
• Epi-lithospermic acid B, lithospermic acid B, and 10-epi-lithospermic acid^[3]
• β-sitosterol^[6]
• Triacontanol (also known as melissyl alcohol)^[6]

The composition of the dried leaves of oregano (excluding the essential oil component) includes a large amount of phenolics, which is fairly standard amongst plants, with the only unique components being phenolic structures known as oreganols (which are structured somewhat similar to rosmarinic acid). Triterpenoids such as ursolic acid may also be active in this plant.

In one sample, the fresh essential oil component of origanum vulgare contained:

• Carvacrol as the major component (characteristic odor of oregano) at 14.5%^[9]
• Thymol (12.6%^[9])
• β-fenchyl alcohol (12.8%^[9])
• δ-terpineol (7.5%^[9])
• γ-terpinene (11.6%^[9])
• α-terpinene (3.7%^[9])
• 1-methyl-3-(1-methylethyl)benzene (6.8%^[9])

These amounts may differ substantially, however.

The essential oil of oregano is high in both carvacrol as well as thymol. Some other components, such as β-fenchyl alcohol or γ-terpinene, may be in high enough levels to be active. Some products claim to contain largely carvacrol though without laboratory confirmation it is difficult to know.

There is a pink flowered variant of oregano (origanum vulgare subspecies vulgare) which has a different essential oil composition which is high in β-Caryophylline (15.6-17.2%), Sabinene (2.5-9.1%), Spathulenol (5.3-6.1%), γ-Eudesmol (5.0-6.7%), p-cymeme (3.3-3.9%), α-humulene (2.1-2.8%), Germacrene D (4.5-9.8%), as well as β-ocimene structures such as (Z)-β-ocimene (0.8-4.0%), (E)-β-ocimene (0.9-3.9%), and allo-ocimene (1.1-4.0%) with various lesser components.^[10] This variant does not appear to have a high carvacrol nor thymol content.

Other species of oregano may not have a high carvacrol content and have a widely different composition.

The water extract of oregano appears to be able to induce analgesia when injected into the brain of rats, and both agonizing or antagonizing the GABA_A receptors or inhibiting the GABA_B receptors can block its effects while activating the GABA_B receptors with baclofen augments it.^[11]

The water extract of oregano contains components that may interact with GABAergic neurotransmission after injection into the rat brain, but the relevance of this information towards oral supplementation in humans is not known.

Intracerebral injections of a water extract from origanum vulgare appear to have analgesic properties in response to both a thermal and tail flick latency test^[11] while intraperitoneal injections have shown efficacy in a formalin test.^[12] These analgesic effects are thought to interact with GABAergic signalling since baclofen (GABA_B agonist able to cause analgesia via these receptors^[13]) augmented the analgesic properties while CGP₃₅₃₄₈ (GABA_B antagonist) blocked the effects, and both GABA_A agonism (muscimol) and antagonism (bicuculline) block the effects of oregano water extracts.^[11]

Injections of oregano may reduce pain in rats, but this has yet to be seen with oral ingestion in humans, so its practical relevance to supplementation is not yet known.

A water extract of oregano (0.2-240mg/L) as well as the essential oil of oregano (2-4mg/L) appear to have in vitro antioxidative properties on LDL oxidation.^[5]

Oregano can reduce LDL oxidation in vitro, but the effect on LDL oxidation following oral supplementation is not yet known.

The oil of oregano has traditionally been used as an anti-infective agent and antibacterial essential oil. The water extracts (teas) are used as carminative agents but do not appear to possess antibacterial properties, but do possess antioxidative properties.^[9] The oil component has been used in conjunction with meat products or fruits (during storage) to reduce microbial growth^[9][14] and to combat common microbes that grow in food products such as Salmonella enterica, Listeria monocytogenes, and Escherichia coli (MIC 3.12µg/mL).^[10][15] The antioxidative properties of oregano are also desirable for the purpose of food preservation, as it can reduce oxidation of fatty acids in the food product with prolonged storage^[16] and preserve the quality of oil products such as olive oil.^[17][18]

The oil of oregano can be used in food production due to its antioxidant properties (preserving fatty acids from spoiling over time during storage) and its antimicrobial properties, since the oil seems to be able to suppress the growth and destroy the common food-borne microbes that cause illness.

Oil of oregano appears to have efficacy against a large range of bacteria, including Bacillus cereus and Bacillus subtilis (MIC 1.56µg/mL^[10]), Staphylococcus aureus (MIC 3.12µg/mL or 0.6-1.25µL/mL^[10][19]), and Eimeria tenella.^[20] The antibacterial properties are thought to be tied to the bioactive carvacrol, which is active on its own.^[21]

The antibacterial properties of oregano oil extend beyond bacteria found in the food supply. This is thought to be due to the carvacrol component, since it is active on its own.

Origanoside has been noted to inhibit tyrosinase activity in cell culture at 10-20μg/mL by 16.9–28.6% (melanoma B16 cells) which was less than the references of arbutin or Vitamin C, suggesting possible comsmetic use in whitening skin.^[22]. Additionally, origanol A has shown inhibitory properties on mushroom tyrosinase activity (IC₅₀ of 2.47μg/mL) which is slightly less than the reference of kojic acid (1.75μg/mL), while origanol B was mostly inactive.^[6]

When applied to the skin of mice, a topical gel containing origanoside over 10 days showed whitening properties associated with reducing the expression of pigment-forming genes (MITF, tyrosinase, and TRP-2).^[22]

In vitro and animal studies suggest that phenolic compounds in oregano may have skin whitening properties when applied topically, although there is currently no evidence on human skin supporting this use.

In adults with chronic fatigue and gastrointestinal complaints, all those who tested positive for fecal parasites (14 out of a total of 33 people testing positive for blastocytis hominis, entamoeba hartmanni, or endomalix nana) who were then administered 600mg oil of oregano daily for six weeks had a reduction in parasite counts, and most (77%) experienced an elimination of parasites.^[23] Alongside the reduction in parasites was a reduction in symptoms of fatigue and gastrointestinal complaints. Noteably, this study was funded by a producer of oregano oil, and no placebo control was used in this study.^[23]

One study has shown a significant reduction in intestinal parasites in those infected, which resulted in a reduction of gastrointestinal and fatigue symptoms when the parasites were eliminated. This lone study has some issues (no placebo control and funded by an oregano oil manufacturer) and has not been replicated.