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Oil of Oregano: Weapon Against the Flu?
By Marissa Beck, MS, RD

Take a whiff or a taste of oil of oregano and feel the aromatic minty burn. Herbalists believe the oil has antiviral, antioxidant, anti-inflammatory, antifungal, antibacterial, and antiparasitic properties. Although the oil has existed for centuries, it has recently started appearing in eyedropper bottles at the checkout corral in supermarkets. With the H1N1 pandemic knocking on 2010’s door, complementary and alternative medicine is gaining popularity. But are those considering this oil for medicinal use on the right track?

A Look at the Research
Results from a 1999 study published in the Journal of Applied Microbiology showed favorable antibacterial and antimicrobial effects. Hammer and colleagues found that oil of oregano’s main activity was due to two phenolic compounds: carvacrol and thymol. These compounds act as bacteriostatic agents on harmful microbes, meaning the oil inhibits replication but doesn’t necessarily kill the bacteria. Their findings also demonstrated the oil’s ability to inhibit growth of some fungi and parasites.

A 2005 study in Molecular and Cellular Biochemistry, conducted by researchers from the department of physiology and biophysics at Georgetown University Medical Center, examined oil of oregano (Origanum) in vitro to determine its effects on Staphylococcus aureus, Bacillus anthracis Sterne, E. coli, Klebsiella pneumoniae, Helicobacter pylori, and Mycobacterium terrae. Origanum inhibited all of the tested organisms except for B. anthracis Sterne. The researchers postulated that Origanum alone or combined with antibiotics might prove useful in preventing and treating severe bacterial infections, especially those that are difficult to treat and/or are antibiotic resistant.1

Oregano oil has also been shown to be a potent antioxidant. A 1996 study by Lagouri et al in the International Journal of Food Sciences and Nutrition identified the major antioxidative fraction of the oil to have tocopherols (vitamin E), which are known to fight free radical damage.

However, a 2006 clinical trial by Nurmi et al in the Journal of Agricultural and Food Chemistry yielded varying results when researchers tested this antioxidative concept on humans. The study randomized 45 healthy nonsmoking males to consume mango-orange juice (placebo), mango-orange juice enriched with 300 mg/day of oregano extract, or mango-orange juice enriched with 600 mg/day of oregano extract for four weeks. Although the researchers noted that there was a significant difference in the excretion of phenolic compounds in the 600 mg/day group compared with the placebo group, there were no short- or long-term effects on the biomarkers of lipid peroxidation. This means that despite high amounts of the oregano extract in the body, free radicals were still dominant.

But can the oil help stave off this year’s flu? Preclinical in vitro studies administered by M. Khalid Ijaz, DVM, PhD, show that wild oregano oil alone and then in combination with cumin, sage, and cinnamon oils (Oregacillin) reduced the strength of human influenza virus A2. (H1N1 is a subtype of this virus.) To note, the test agents used were Oreganol P73 and Oregacyn, both extracts manufactured by North American Herb & Spice, the company sponsoring these antiviral studies. The antiviral activities of two Oreganol P73-based spice extracts were evaluated during in vitro human coronavirus infection. The virus was exposed to the oregano oils and researchers collected samples at various times postexposure. Results indicated that Oreganol P73 and Oregacyn inhibited the human coronavirus infection in vitro. These findings do not necessarily indicate that oil of oregano can act as a preventative measure for this season’s flu.1

Indications and Usage
A typical dose of oregano oil is 100 mg three times daily via a liquid or as capsules. In either form, dietitians should help clients verify that the product is derived from the correct oregano plant (Origanum vulgare). Additionally, the product should contain 55% to 65% of the phenolic compound carvacrol.

Research to date has not proven the efficacy of using oil of oregano to treat respiratory disorders, herpes simplex virus outbreaks, rheumatoid arthritis, and urinary tract disorders, yet some companies that produce oil of oregano make claims for those medicinal purposes. Additionally, although much of the literature is promising for the antimicrobial, antiparasitic, antifungal, and antioxidant effects of consuming the oil, researchers have yet to complete any meaningful, well-done studies at the viral level.

Drug Interactions and Side Effects
Although no drug interaction data are available, oil of oregano may cause sensitivities in those with allergies to thyme, basil, mint, or sage since the oregano plant belongs to the same family. Additionally, oil of oregano’s safety is questionable in young children and pregnant or nursing women, and it is contraindicated for people with severe liver or kidney disease.

Bottom Line
Even though Web sites tout oil of oregano’s anti viral properties, the research doesn’t fully support this aspect of the oil. Many companies selling oil of oregano will sponsor studies that suggest antiviral properties, but these studies do not appear in standard literature searches for that exact reason. As a result, dietitians must be skeptical when they or their clients find data that “prove” antiviral properties of the oil. Note, however, that oregano oil does have antimicrobial properties that can help keep illnesses at bay.

For those concerned about contracting the flu virus this season, the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices recommends that high-risk populations receive the vaccine. For the tech-savvy, the iPhone application called Outbreaks Near Me, which alerts users to any known flare-ups of the flu in their area, is a helpful tool. For those who are not in the smartphone crew, healthmap.org provides the same information.

No matter how the Western world chooses to confront illness this season, Chinese medicine and Mediterranean cultures have used oil of oregano for centuries specifically for colds, fever, vomiting, and dysentery. Oregano oil may not win the battle against the Swine flu alone, but its myriad antibacterial properties are favorable and may help keep people healthy this winter.

— Marissa Beck, MS, RD, is a health writer and dietitian based in New York City.

1. Ijaz MK, Chen Z, Raja SS, et al. Antiviral and virucidal activities of oreganol P73-based spice extracts against human coronavirus in vitro. Presented at: Seventeenth International Conference on Antiviral Research; May 2-6, 2004; Tucson, Ariz.