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Nutrition Today:
doi: 10.1097/NT.0b013e3181dec789
Food Science

Oregano: Overview of the Literature on Health Benefits

Singletary, Keith PhD

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Keith Singletary, PhD, is Professor Emeritus of Nutrition, Department of Food Science & Human Nutrition, University of Illinois, Urbana, Illinois.

This study was supported by McCormick Science Institute.

Correspondence: Keith Singletary, PhD, Department of Food Science and Human Nutrition, University of Illinois, Urbana, IL 61801 (

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Oregano is an herb that has been cultivated for centuries in the Mediterranean area, although it now can be found on most continents. Actually, there is not simply one "oregano," but rather several species that may contribute to the oregano used for culinary purposes. Origanum vulgare (also referred to as Spanish thyme and wild marjoram), a member of the plant family Lamiaceae, is generally the spice variety sold as oregano in Europe and the United States. Medicinal uses for oregano date back to the ancient Greek and Roman empires where applications of the leaves were used to treat such maladies as skin sores and relieve aching muscles and as an antiseptic. Oregano also has been used in traditional medicines for such ailments as asthma, cramping, diarrhea, and indigestion. In Greece, an oregano infusion is still used as a folk remedy against colds and upset stomach and to maintain general health. Based on the current scientific literature, oregano extracts and individual constituents consistently have demonstrated antimicrobial actions in vitro toward food-borne pathogens, although the capacity to counter human infections is not well studied. Oregano contains several potent antioxidants that may contribute to the findings in preliminary studies that oregano exhibits benefits toward the cardiovascular and nervous systems, relieves symptoms of inflammation, and modulates blood sugar and lipids. Well-controlled human studies substantiating these health effects are lacking

Oregano is an herb that has been cultivated for centuries in the Mediterranean region, although now it can be found in most continents. The name oregano translates roughly into "mountain joy," which explains in part its association for ancient Greeks and Romans with joy and happiness. Actually there is not simply one "oregano," but rather several species that may contribute to the oregano used for culinary purposes. Origanum vulgare (also referred to as Spanish thyme and wild marjoram), a member of the plant family Lamiaceae (Labiatae), is generally the spice variety sold as oregano in Europe and the United States. Its light green leaves are used either "dry" or "fresh" as a culinary seasoning, and its use has elicited such sensory responses as "pungent," "pleasantly bitter," "herbaceous," and "aromatic," to name a few. Two constituents of oregano, carvacrol and thymol, contribute to the sensation of warmth in the mouth due to their actions on temperature-sensitive structures called ion channels.1,2

Oregano is most well known for imparting an "Italian taste" to Mediterranean cuisine and may be used to enhance the flavors of a variety of foods including baked goods, vegetables, legumes, fish, pizza, pasta sauce, and chilis. It has been included in aromatic teas and is a frequent addition to Mexican dishes. Mexican oregano is prepared from Lippia spp (Verbenaceae).3 In the Philippines, a related herb suganda (Coleus amboinicus) also is used as oregano in cooking.4

Medicinal uses for oregano date back to the ancient Greek and Roman empires where applications of the leaves were used to treat skin sores, to relieve aching muscles, and as an antiseptic. Oregano also has been used in traditional medicines for such ailments as asthma, cramping, diarrhea, and indigestion.5 In Greece, an oregano infusion is still used as a folk remedy against colds and an upset stomach and to maintain general health.6

Because there are so many species of Origanum used around the world as an "oregano" condiment and for medicinal purposes, it is not surprising that there are variations in their profiles of bioactive constituents and in the purported beneficial effects.7-12 For example, the carvacrol content of essential oils from Origanum plants may vary over 20-fold, and similarly thymol content may vary 3-fold to almost 30-fold among plant oils.7,9 The amounts of the terpene alcohol linalool could range from nondetectable in one plant oil to approximately 30% of the essential oil composition of another.9

The volatile compounds carvacrol (isopropyl-o-cresol or 5-isopropyl-2-methylphenol) and thymol (isopropyl-m-cresol) are considered major terpene components of oregano essential oils,7,9,13 along with p-cymene (4-isopropyl toluene) and γ-terpinene, which are precursors in the biosynthesis of thymol and carvacrol. Thymol is used in perfumes and mouthwashes. Other bioactive compounds identified in oregano leaf include phenolic acids (caffeic acid, p-coumaric acid), rosmarinic acid and caffeoyl derivatives, ursolic acid, and carnosic acid, as well as a mixture of flavonoids.5 In fact, rosmarinic acid is one of the most abundant phenolic compounds present in aqueous extracts of oregano leaf and is known to be the dominant phenolic compound in Labiatae spices (such as oregano, rosemary, sage, etc).5

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It should be mentioned at the onset of this overview of oregano and health that the benefit of oregano to humans ultimately will depend on the bioavailability of its biologically active constituents following ingestion, that is, how well those components are absorbed, distributed, metabolized, and eliminated from the body. This will be of critical importance in establishing any link between health effects detected in vitro and those that might be expected to occur in vivo. Investigations evaluating the bioavailability of oregano in humans are limited. Two reports in humans have indicated that the intake of oregano extracts containing doses of 300 to 600 mg/d total oregano-derived phenolics resulted in the absorption and quick elimination of the phenolic acids.14,15 Yet, even given a dose of 600 mg/d for 4 weeks, no significant changes in biomarkers of lipid peroxidation were detected in these subjects.14 A number of issues were identified by the authors of this study that may explain variations in natural product bioavailability and bioactivity. For example, the bioactivity of metabolites of a parent antioxidant phytochemical can be markedly different than that of the parent compound. Also, phytochemicals in a complex mixture may differ individually in their extent of absorption, their manner of metabolism, and thus their distribution in various body tissues. The bioavailability of single compounds identified in oregano, such as rosmarinic acid and thymol, also has been reported. In a clinical trial involving 12 healthy volunteers, the systemic availability and pharmacokinetics of thymol following a single 1.08-mg dose were examined. The metabolite thymol sulfate was detected in plasma, with a half-life of 10.2 hours16 and a maximum plasma concentration of approximately 93 ng/mL. In another small clinical trial, 6 healthy men were given a single oral dose of 200 mg rosmarinic acid in an extract of Perilla frutescens.17 They observed that rosmarinic acid was absorbed and detected in sulfate- and glucuronide-conjugated forms, with 75% of the rosmarinic acid metabolites being rapidly excreted within 6 hours after intake. Similar results were obtained in a study in rats orally administered rosmarinic acid at 50 mg/kg body weight.18 The absorption efficiency of rosmarinic acid in rats was determined to be much less than that of other phenolic acids such as caffeic acid and p-coumaric acid following a 100-μmol dose per kilogram of body weightt.19 This important area of study in humans warrants additional attention.

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A variety of health benefits of oregano or its individual constituents have been the subject of scientific study. Oregano extracts and individual constituents consistently have demonstrated antimicrobial actions in vitro toward food-borne pathogens, although the capacity to counter human infections is not well studied. Oregano contains several potent antioxidants that may partly contribute to findings in preliminary studies in which oregano exhibits benefits toward the cardiovascular and nervous systems, relieves symptoms of inflammation, and modulates blood glucose and lipid levels. Well-controlled human studies substantiating these health effects are lacking.

Examples of several uses for oregano are presented in the following, and an effort was made to give an overview of the variety of scientific research on this topic. Points of view for rating of evidence in each category are based on consideration of cell culture and animal and human clinical data from the peer-reviewed scientific literature. A higher rating was given when there were both preclinical and clinical data and when there was consistency of findings among well-controlled human studies.

The safety of oregano extracts and individual constituents for medicinal use in humans has not been thoroughly studied. The German Commission E and the American Herbal Products Association have reported no known safety risks associated with typical uses of oregano leaf. A similar report for the essential oil has not been issued.117,118 Furthermore, the Commission E does not recommend therapeutic use of this herb, because efficacy has not been well documented. An aqueous distillate of Origanum onites L containing carvacrol as the major constituent was shown to be nontoxic in acute and chronic preclinical toxicity models,119 and carvacrol is not hepatotoxic in the rat.114 Some oregano constituents such as the monoterpenoids carvacrol and thymol are known to be activators of the transient receptor potential channel (TRPV3), although they do not consistently induce skin sensitization120,121 and are not skin irritants.1 There are a few cases of systemic allergic reactions following ingestion of oregano.122 In light of the concern that the volatile components of oregano oil can be irritating to mucous membranes, it has been recommended that the oils not be applied topically to mucous membranes at greater than a 1% concentration.123 Oregano essential oil administered in the diet at 0.1% to female mice for 2 weeks resulted in a significant increase in cell death of mouse preimplantation embryos.124 Dose-response effects of oregano essential oil following internal use in humans have not been well characterized, especially considering the potential variability in bioactive component profiles. Oregano was reported to have biological activity as a progestin in in vitro assays.125 However, because the bioavailability of oregano and any subsequent effects on hormones have not been well studied in vivo, the biological significance of these in vitro findings, if any, remains to be determined.

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Oregano has several properties that deserve further characterization and confirmation. It is clear that oregano's chemical constituents can suppress the growth of a broad range of microorganisms in vitro. The conditions under which it can act effectively to counteract microbial contamination in food products need to be better examined. Particularly valuable will be characterization of the conditions under which its constituents may combat human infection.20 There is limited but suggestive evidence that oregano bioactive components may suppress inflammation and improve blood glucose and lipid regulation. Such properties warrant additional preclinical evaluation to determine the active agents, potential mechanisms, and consistency among experimental models. In particular, confirmation of the potential capacity of oregano to decrease hyperglycemia and enhance insulin sensitivity and the doses necessary to do so warrant further investigation. Lastly, despite numerous reports that oregano's phytochemicals have antioxidant actions in vitro, the in vivo evidence in animals is limited and in humans is unsubstantiated.14 This lack of effect clinically in part may be due to poor oral bioavailability that has been observed. Thus, it will be of value to determine the specific oregano extracts, active constituents, effective doses, and conditions for which oregano may have measurable impact on markers of antioxidant status in humans after supplementation.14

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Vitamin D Deficiency Likely Among Some Kidney Disease Patients Starting Dialysis

Vitamin D deficiency is very common among patients with kidney disease who have low blood protein levels and who start dialysis during the winter according the results of a new study. The research identifies a group of patients who are at extremely high risk of being deficient in vitamin D and provides some clues as to why the deficiency occurs in them. Vitamin D deficiency is common in patients with end-stage renal disease on dialysis, but it is not clear which patients are at increased risk. The study sought to determine whether routinely measured clinical and demographic characteristics could identify dialysis patients who have a high risk of vitamin D deficiency. Researchers analyzed data from 908 patients in the ArMORR (Accelerated Mortality on Renal Replacement) cohort, a nationally representative group of US dialysis patients. Data from 60% of the patients were used to find potential predictors of vitamin D deficiency, whereas data from the other 40% of patients were used to validate the predictors. Fully 79% of the study population was vitamin D deficient. Black race, female sex, winter season, and low blood levels of the protein albumin (≤3.1 g/dL) were the strongest predictors of vitamin D deficiency. In the validation set, the presence of low blood albumin levels and winter season increased the likelihood of vitamin D deficiency in black females (from 90% to 100%), black males (from 85% to 100%), white females (from 82% to 94%), and white males (from 66% to 92%).One interpretation of the finding that low blood albumin levels were associated with deficiency is that at-risk patients leak large amounts of protein in their urine. The investigators suspect that vitamin D-binding protein, which transports the vitamin through the blood, may also be lost through the urine. Its loss could lead to the loss of vitamin D as well. In addition, whereas previous studies have demonstrated that patients on dialysis have an impaired ability to generate vitamin D from sun exposure, these findings emphasize that skin-based production of the vitamin is likely to be important in patients with end-stage renal disease.

Source: Clin J Am Soc Nephrol. 2010;5:460-467.

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Dairy Avoiders: Are You Getting Enough?

Lactose intolerance is a real and important clinical syndrome, but quantifying its public health burden is challenging. A National Institutes of Health Consensus Development panel recently assessed the available evidence on lactose intolerance and health across the age spectrum and across racial and ethnic groups. Many individuals with diagnosed or perceived lactose intolerance avoid dairy products, which constitute a readily accessible source of calcium, other nutrients, and vitamin D (when fortified). Inadequate consumption of these nutrients may increase the risk for chronic health problems, including osteoporosis and decreased bone health. The panel defined lactose intolerance as the onset of gastrointestinal symptoms-diarrhea, abdominal pain, flatulence, and/or bloating-after ingesting lactose-containing foods and beverages; this is due to deficient levels of lactase, an enzyme necessary to break down lactose. Lactose malabsorption occurs when lactose is incompletely broken down in the intestine, which may or may not result in gastrointestinal symptoms after eating dairy products. Reduction of lactase enzyme in humans occurs in childhood and persists through the life span in most individuals (lactase nonpersisters). These individuals may or may not have the gastrointestinal symptoms of lactose intolerance. Understanding the distinction and interplay between these conditions is important when considering ways to meet nutritional needs.

For diagnosed lactose-intolerant individuals, multiple management strategies have been proposed. These include distributing lactose intake throughout the day and/or combining it with other foods, choosing nondairy foods rich in the nutrients found in dairy products, taking dietary supplements, ingesting incremental amounts of dairy products over time to increase tolerance, consuming reduced-lactose dairy products, and using probiotics (in supplements and foods). The panel emphasized the need for additional research to better understand the effectiveness of these approaches for decreasing symptoms, optimizing nutritional intakes, and improving health outcomes, with special emphasis on diverse populations. Depending on a variety of factors, some affected individuals could be counseled on ways to increase dairy intake, whereas others could be urged to meet nutrient requirements from other sources. For example, studies show that when consumed with other foods, even individuals diagnosed with lactose malabsorption can consume at least 1 cup of milk with few or no symptoms.


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