INTRODUCTION

Avena sativa is a member of the grass (Poaceae) family and an annual with tall, hollow stems that can grow up to 1.2 meters (approximately four feet) in height.^1,2 The stems produce flat, bladelike leaves and loosely branched inflorescences, or panicles, that produce golden seeds. These seeds, or groats, are the main part of the plant used commercially, though the immature seeds and fresh or dried aerial parts are used in medicinal preparations. When unripe, the seeds are referred to as “milky” oats. Ripened seeds are dried and often processed into flakes for human consumption.

Oat is native to the Fertile Crescent, an area that spans from Israel to Iran, but it has been naturalized throughout temperate areas of the globe and cultivated for approximately 3,000 years.³ Avena sativa is thought to be descended from a wild ancestor, A. sterilis. It grows well in cool, damp climates but is adaptable and tolerates soil with high salinity.⁴ Avena sativa is one of 25 accepted species in the genus Avena, which includes other species of oat that are not as easily adaptable or cultivated outside of their native regions, including A. byzantina in Turkey, A. strigosa in the western Mediterranean, and A. abyssinica in Ethiopia.³

HISTORY AND CULTURAL SIGNIFICANCE

The name Avena sativa was first published in Swedish botanist Carl Linnaeus’ Species Plantarum in 1753. “Avena” was the Roman word for the oat plant, while “sativa” means “cultivated.” In Northern Europe, oats were cultivated widely for both human and animal consumption. However, ancient Romans and Greeks considered oat a weed and used it most often for animal fodder. Roman naturalist Pliny the Elder (ca. 23–79 CE) referred to oats as “the barbaric bread grain of the Germans.”⁵

Oat was not widely regarded as a medicinal ingredient until the Middle Ages in Europe. As the use of oat spread in traditional Western medicinal practices, both dried and fresh oats were used for a wide variety of conditions, including anxiety, stress, skin diseases, bladder disorders, blood vessel and lung ailments, and gastrointestinal disorders.¹ German physician and botanist Adam Lonicer (1528–1586) wrote in his 1557 herbal treatise Kräuter-Buch that oats were not only nutritious but also useful in poultices, to treat fistulas (abnormal connections between organs or vessels that do not ordinarily connect), and as a diuretic.⁶ Italian naturalist Pietro Mattioli (also known as Matthiolus; 1501–1577) recommended oat porridge for constipation and in a poultice or wash for swollen limbs, to clear the complexion, and to treat scabs in children.⁵

In the modern Western herbal tradition, oats are considered a nervine, relaxant, antispasmodic, antidepressant, demulcent (substance that relieves irritation of mucous membranes), and restorative.⁷ In the US Eclectic medical tradition of the 19th and early 20th centuries, oats were used, in the words of physician Finley Ellingwood, MD, as a “remedy of great utility in loss of nerve power and in muscular feebleness from lack of nerve force.”⁸ The German Commission E monographs list oat straw (stems and leaves) as an approved herb for external application in the case of “inflammatory and seborrheic skin disease, especially those with itching.”⁹ The Commission E also records uses of oat herb “for acute and chronic anxiety, stress and excitation, neurasthenic and pseudoneurasthenic syndromes [conditions associated with physical and mental exhaustion], skin diseases, connective tissue deficiencies, weakness of the bladder, and as a tonic and roborant [restorative],” though these claims were not approved uses. In 1995 and later, the Commission E monographs were superseded by the formation of the European Medicines Agency (EMA) as part of the European Union.

Milky oats also have been used, particularly in Indian medicinal practices, as a therapy for opium (derived from the opium poppy, Papaver somniferum, Papaveraceae) and tobacco (Nicotiana tabacum, Solanaceae) addiction and to ease the symptoms of withdrawal.⁴ In traditional Persian medicine, oats were used topically for their emollient effects and added to baths, poultices, and creams to soothe inflamed or itchy skin and other skin disorders.¹⁰ According to a 2015 survey, A. sativa was among the top 12 most commonly identified plants used in folk medicine in northwest Pakistan, where oats are fried in ghee (a type of clarified butter) and milk to make a paste that is used as an aphrodisiac and general body tonic.¹¹

Oat ranks sixth in world grain production after other species in other genera in the Poaceae family: corn (Zea mays,), rice (Oryza sativa), wheat (Triticum aestivum), barley (Hordeum vulgare), and sorghum (Sorghum bicolor). However, oat production has increased significantly since the 1990s.¹² The top oat-producing countries are Russia, Canada, the United States, and Poland.² The oat plant, which accumulates calcium, nitrogen, and magnesium, often is used as a cover crop to regenerate soil.¹³

CURRENT AUTHORIZED USES IN COSMETICS, FOOD, AND MEDICINE

In the United States, oat protein and beta-glucans (also written as “β-glucans”; a type of polysaccharide) derived from oat are Generally Recognized as Safe (GRAS) by the US Food and Drug Administration (FDA) for general use in foods and, in the case of beta-glucans, as a source of fiber.^14,15 As a food product, oat seeds are dried and sold as either whole groats, flattened into flakes (rolled oats), or flattened and pulverized for “instant” oatmeal. Oatmilk, a decoction of pulverized oat groats in water, is a dairy-free alternative “milk.” Oats can also be used in the grain mash to make beer.

The FDA has allowed products containing three grams or more of beta-glucans from oat, oat bran (the outer layer of the groat), rolled oats, and whole oat flour to include a health claim that “Soluble fiber from foods such as oat bran, oatmeal, or whole oat flour, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease.”¹⁶ Additionally, colloidal oatmeal (oat grains ground to a fine powder) prepared to the standards set by the United States Pharmacopeia is approved as an ingredient in over-the-counter products that can claim that they temporarily protect and help relieve minor skin irritation and itching due to rashes, eczema, poison ivy (Toxicodendron spp., Anacardiaceae), poison oak (T. diversilobum), poison sumac (T. vernix), or insect bites.¹⁷

In Canada, oat seed, oat seed bran, oat seed oil, oat grass (herb), oat sprout extracts, and colloidal oatmeal are regulated medicinal ingredients that are licensed natural health products (NHPs), which require pre-marketing authorization from the Natural and Non-prescription Health Products Directorate (NNHPD). Oat seed extract product uses include as headache relief, a nervine/calmative, and a “source of antioxidants/provide antioxidants that help fight against free radicals,” while colloidal oatmeal is indicated for the relief of minor skin irritation and itching due to rashes, eczema, poison ivy, poison oak, or poison sumac, insect bites, and dry, itchy skin.^18-20

The European Food Safety Authority (EFSA) allows foods with oat ingredients to use the health claim that “Oat grain fiber contributes to an increase in faecal bulk.”²¹ Foods containing at least four grams of oat-derived beta-glucans per 30 grams of carbohydrates can use this claim: “Consumption of β-glucans from oats as part of a meal contributes to the reduction of the blood glucose rise after that meal.” The EFSA also concluded that “oat beta-glucan has been shown to lower/reduce blood cholesterol. Blood cholesterol lowering may reduce the risk of (coronary) heart disease.”²²

The EMA’s Committee on Herbal Medicinal Products (HMPC) has monographs for “Avenae herbae” (oat herb/oat straw) and “Avenae fructus” (oat grain). For oat grain, the HMPC concluded that it is a “traditional herbal medicinal product for the symptomatic treatment of minor inflammations of the skin (such as sunburn)” and “an aid in healing of minor wounds,” while oat herb preparations are a “traditional herbal medicinal product for relief of mild symptoms of mental stress and to aid sleep.”^23,24

MODERN RESEARCH

Much of the current literature on oat focuses on oat-derived beta-glucans and oat fiber on cardiovascular health markers and the topical use of oat extract in cosmetics. Extracts of milky oat have also been investigated based on their traditional use as a nervine (Table 1).

Oat groats contain dietary fiber, protein, and other macronutrients; B vitamins such as thiamin; vitamin E in the form of alpha-tocopherol; and minerals such as manganese, magnesium, and phosphorous.² Among cereal grains, oat is notable for having a high protein content, ranging from 15% to 20% of the groat by weight.¹² Beta-glucans are a form of soluble dietary fiber that ferments in the colon and aids with carbohydrate and lipid metabolism. Intake of oat beta-glucans is associated with reductions in blood pressure, postprandial glucose concentrations, and cholesterol levels, which in turn can lower the risk of cardiovascular disease (CVD). Rolled oats contain approximately 4% beta-glucans.² Other polysaccharides in oat include arabinoxylan, which also can support blood glucose regulation.^25,26

Oat groats also contain avenanthramides, antioxidant phenolic compounds that were first identified in oat. Avenanthramides have been shown to exhibit anti-inflammatory, antiproliferative, and anti-itching activities in vitro and in vivo. Avenanthramides have potential cancer preventive activities and may help with degenerative conditions such as atherosclerosis and osteoporosis.²⁷ Oat contains other polyphenols including apigenin, kaempferol, luteolin, quercetin 3-O-rutinoside, and sinapoylquinic acid.²⁶ These compounds aid in glucose and lipid metabolism and have demonstrated antimicrobial, antioxidant, and neuroprotective activities.

The flavonoid and saponin content of oat groats, including isoorientin-2’’-Ο-arabinoside, isovitexin-2’’-O-arabinoside, and avenacosides A and B, also contributes to the anti-inflammatory properties.28 Thirteen triterpenoid saponins have been identified in oat bran, and these saponins are present to varying degrees in commercial oat products.²⁹ Saponins have anticancer, antioxidant, and cholesterol-lowering activities. Oat extracts have exhibited high levels of antifungal and antimicrobial activities, which are attributed to the presence of class I chitinase. Though class I chitinase is present in most cereal grains, oat seed extract contains 10 times more of this compound compared to wheat, barley, and rye (Secale cereale, Poaceae) seed extracts.³⁰

Numerous studies have assessed the effects of oat consumption in a variety of forms, including oat-derived beta-glucans, on cardiovascular health markers, including cholesterol levels, blood pressure, endothelial function, and vasodilation. Multiple systematic reviews have found that daily oat supplementation is associated with significant reductions in blood pressure, total cholesterol (TC), and low-density lipoprotein (LDL) cholesterol levels and enhanced production of nitric oxide, which can aid in the prevention of atherosclerosis.^2,31-33 These results were observed in healthy adults as well as adults who had mild to moderate hypertension. Dose, length of intervention, and disease severity impacted outcomes, and daily supplementation over a long period of time produced the most significant results in one review.³¹ In one clinical trial, oat consumption correlated with a greater reduction in body mass of overweight adults compared to placebo. The participants who consumed oats also showed improvements in hepatic function.²

Preclinical studies have confirmed that oat interacts with neurotransmitters associated with cognition, memory, and motivation. In humans, both milky and dried oat consumption has been associated with antidepressant and antianxiety activity, especially in participants with menopause, and a large dose of oat extract improved attention and concentration in older adults.² Specifically, milky oat has been shown to have a significant inhibitory effect on monoamine oxidase B (MAO-B) and phosphodiesterase 4 (PDE-4) enzymes, which can deactivate monoamine neurotransmitters and are implicated in some psychiatric and neurological conditions. These activities may increase dopaminergic availability and cerebral vasodilation.³⁴ Currently, proprietary milky oat extracts are being tested for their effects on cognition and working memory.^34,35

Studies on the topical use of oat and oat extracts have shown that these preparations are useful in treating inflammatory conditions including acne, atopic dermatitis (or atopic eczema), and pruritis (itchy skin). Oatmeal preparations also showed mild protection against skin damage from ultraviolet rays.² Several compounds in oat have anti-inflammatory and immunomodulatory actions that can inhibit prostaglandin production and T-cell proliferation.²⁸

Oat extract was found to improve opioid and tobacco withdrawal symptoms in animal studies.^2,36 However, few studies have investigated this use in humans, and the results are mixed. In open, uncontrolled studies, participants who used opium showed a varied response to supplementation with milky oat extract, with some ceasing use entirely and some maintaining their current habit; in a study of participants who smoked cigarettes, a slight trend toward smoking cessation was noted, with a stronger effect seen in light smokers than for heavy smokers.²

ADULTERATION AND SUBSTITUTION

The US Department of Agriculture permits a certain level of wild oat relatives to be mixed with Avena sativa, as they often can be found growing together. While the monograph for “Common oat for homeopathic preparations” of the French Pharmacopoeia⁴⁴ lists A. elatior as a potential adulterant, other sources indicate that oat adulteration occurs very rarely in practice.⁴⁵

Oats are a popular source of fiber and carbohydrates for those who are gluten-intolerant. Though oats do not naturally contain gluten, many commercial brands are processed in factories where cross-contamination may be present. Brands that process oats in a separate facility often label those products as “gluten-free” to advertise this fact.

SUSTAINABILITY AND FUTURE OUTLOOK

Avena sativa is widely cultivated on a global commercial scale and not considered threatened. Wild species of oat, including A. fatua and A. sterilis, are listed under the category of “least concern” according to the International Union for Conservation of Nature Red List.^46,47

References

1. Oat. American Botanical Council website. Available at: www.herbalgram.org/resources/healthy-ingredients/oat/. Accessed June 2, 2022.
2. Al-Snafi AE. The nutritional and therapeutic importance of Avena sativa — An overview. International Journal of Phytotherapy. 2015;5(1):48-56.
3. Avena sativa L. Plants of the World Online. Royal Botanic Gardens, Kew. Available at: https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:391732-1. Accessed August 3, 2022.
4. Alaoui SB. Avena sativa. Ecoport Project. June 3, 2017. Available at: http://ecoport.org/ep?Plant=481&entityType=PL****&entityDisplayCategory=full. Accessed July 11, 2022.
5. Avena sativa L. A. Vogel Plant Encyclopaedia. A. Vogel website. Available at: www.avogel.ch/en/plant-encyclopaedia/avena_sativa.php. Accessed August 4, 2022.
6. Lonicerus A. Vollständiges Kräuterbuch oder das Buch über alle drey Reiche der Natur. Augsburg, Germany; 1783.
7. Felter HW. The Eclectic Materia Medica: Pharmacology and Therapeutics. Cincinnati, OH: J.K. Scudder; 1922.
8. Ellingwood F, Lloyd JU. American Materia Medica, Therapeutics and Pharmacognosy. Chicago, IL: Ellingwood’s Therapeutist; 1915.
9. Blumenthal M, Busse WR, Goldberg A, et al, eds. The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines. Austin, TX; Boston, MA: American Botanical Council; Integrative Medicine Communications; 1999.
10. Parvizi MM, Salami MH, Jazani AM, Javaheri R, Jaladat AM, Handjani F. Complementary and integrative remedies in the treatment of chronic pruritus: A review of clinical trials. J Cosmet Dermatol. May 2022. In press. Available at: https://onlinelibrary.wiley.com/doi/10.1111/jocd.15094. Accessed July 12, 2022.
11. Sher H, Aldosari A, Ali A, de Boer HJ. Indigenous knowledge of folk medicines among tribal minorities in Khyber Pakhtunkhwa, northwestern Pakistan. J Ethnopharmacol. 2015;166:157-167.
12. Bao-Luo M, Zheng Z, Ren C. Oat. In: Sadras VO, Calderini DF, eds. Crop Physiology Case Histories for Major Crops. New York, NY: Academic Press; 2021:222-248.
13. Troup G. Oats: Fertilisers and Plant Nutrition. Department of Primary Industries and Regional Development website. May 22, 2018. Available at: www.agric.wa.gov.au/oats/oats-fertilisers-and-plant-nutrition. Accessed August 4, 2022.
14. US Food and Drug Administration. GRN No. 544: β-glucans from oat bran. October 10, 2014. Available at: www.cfsanappsexternal.fda.gov/scripts/fdcc/?set=GRASNotices&id=544&sort=GRN_No&order=DESC&startrow=1&type=basic&search=oat. Accessed August 4, 2022.
15. US Food and Drug Administration. GRN No. 575: Oat protein. April 15, 2015. Available at: www.cfsanappsexternal.fda.gov/scripts/fdcc/?set=GRASNotices&id=575&sort=GRN_No&order=DESC&startrow=1&type=basic&search=oat. Accessed August 4, 2022.
16. US Food and Drug Administration. 21CFR §101.81 Final Rule: Food Labeling: Health Claims; Soluble Fiber from Whole Oats and Risk of Coronary Heart Disease. Code of Federal Regulations. Washington, DC: Office of the Federal Register, National Archives Administration; 1997;62(61):15343-15344.
17. US Food and Drug Administration. 21CFR §310, 347, and 352 — Skin Protectant Drug Products for Over-the-Counter Human Use; Final Monograph. Federal Register. 2003;68(107):33362-33381.
18. Natural and Non-prescription Health Products Directorate. Monograph: Antioxidants. Ottawa, ON: Health Canada; August 1, 2017.
19. Natural and Non-prescription Health Products Directorate. Medicated Skin Care Products Monograph. Ottawa, ON: Health Canada; 2018.
20. Natural and Non-prescription Health Products Directorate. Monograph: Cognitive Function Products. Ottawa, ON: Health Canada; March 25, 2019.
21. EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific Opinion on the substantiation of health claims related to oat and barley grain fibre and increase in faecal bulk (ID 819, 822) pursuant to Article 13(1) of Regulation (EC) No 1924/2006. EFSA Journal. 2011 June;9(6):2249.
22. EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific opinion on the substantiation of a health claim related to oat beta glucan and lowering blood cholesterol and reduced risk of (coronary) heart disease pursuant to Article 14 of Regulation (EC) No 1924/2006. EFSA Journal. 2010 Dec;8(12):1885.
23. Committee on Herbal Medicinal Products. Community herbal monograph on Avena sativa L., fructus. London, UK: European Medicines Agency; September 4, 2008.
24. Committee on Herbal Medicinal Products. Community herbal monograph on Avena sativa L., herba. London, UK: European Medicines Agency; September 4, 2008.
25. Dapčević-Hadnađev T, Hadnađev M, Pojić M. The Healthy Components of Cereal By-Products and Their Functional Properties. In: Galanakis CM, ed. Sustainable Recovery and Reutilization of Cereal Processing By-Products. Cambridge, UK: Woodhead Publishing; 2018:27-61.
26. Aparicio-Fernández X, Reynoso-Camacho R, Ramos-Gómez M, Mendoza-Sánchez M, Mora O, Pérez-Ramírez IF. Polyphenols and avenanthramides extracted from oat (Avena sativa L.) grains and sprouts modulate genes involved in glucose and lipid metabolisms in 3T3 L1 adipocytes. J Food Biochem. 2021 June;45(6):e13738.
27. Yu Y, Zhou L, Li X, et all. The progress of nomenclature, structure, metabolism, and bioactivities of oat novel phytochemical: Avenanthramides. J Agric Food Chem. 2022 Jan;70(2):446-457.
28. Mandeau A, Aries M-F, Boé J-F, et al. Rhealba® oat plantlet extract: Evidence of protein-free content and assessment of regulatory activity on immune inflammatory mediators. Planta Med. 2011;77(9):900-906.
29. Hu C, Sang S. Triterpenoid saponins in oat bran and their levels in commercial oat products. J Agric Food Chem. 2020;68(23):6381-6389.
30. Sørensen HP, Madsen LS, Petersen J, Andersen JT, Hansen AM, Beck HC. Oat (Avena sativa) seed extract as an antifungal food preservative through the catalytic activity of a highly abundant class I chitinase. Appl Biochem Biotechnol. 2010 Mar;160(6):1573-1584.
31. Yu J, Xia J, Yang C, et al. Effects of oat beta-glucan intake on lipid profiles in hypercholesterolemic adults: A systematic review and meta-analysis of randomized controlled trials. Nutrients. 2022 May;14(10):2043.
32. Ho HVT, Sievenpiper JL, Zurbau A, et al. The effect of oat β-glucan on LDL-cholesterol, non-HDL-cholesterol and apoB for CVD risk reduction: A systematic review and meta-analysis of randomised-controlled trials. Br J Nutr. 2016 Oct;116(8):1369-1382.
33. Othman RA, Moghadasian MH, Jones PJ. Cholesterol-lowering effects of oat β-glucan. Nutr Rev. 2011 June;69(6):299-309.
34. Martinez-Horta S, Ivanir E, Perrinjaquet-Moccetti T, Keuter MH, Kulisevsky J. Effects of a green oat herb extract on cognitive performance and neurophysiological activity: A randomized double-blind placebo-controlled study. Front Neurosci. 2021;15:748188.
35. Kennedy DO, Bonnländer B, Lang SC, et al. Acute and chronic effects of green oat (Avena sativa) extract on cognitive function and mood during a laboratory stressor in healthy adults: A randomised, double-blind, placebo-controlled study in healthy humans. Nutrients. 2020 May;12(6):1598.
36. Ebrahimie M, Bahmani M, Shirzad H, Rafieian-Kopaei M, Saki K. A review study on the effect of Iranian herbal medicines on opioid withdrawal syndrome. J Evid Based Complementary Altern Med. 2015 Oct; 20(4):302-309.
37. Xu D, Wang S, Feng M, et al. Serum metabolomics reveals underlying mechanisms of cholesterol-lowering effects of oat consumption: A randomized controlled trial in a mildly hypercholesterolemic population. Molecular Nutrition and Food Research. 2021;65(9):e2001059.
38. Capone K, Kirchner F, Klein SL, Tierney NK. Effects of colloidal oatmeal topical atopic dermatitis cream on skin microbiome and skin barrier properties. Journal of Drugs in Dermatology. 2020;19(5):524-531.
39. Cicero AFG, Fogacci F, Veronesi M, et al. A randomized placebo-controlled clinical trial to evaluate the medium-term effects of oat fibers on human health: The Beta-glucan Effects on Lipid Profile, Glycemia and inTestinal Health (BELT) study. Nutrients. 2020;12(3):686.
40. Kennedy DO, Jackson PA, Forster J, et al. Acute effects of a wild green-oat (Avena sativa) extract on cognitive function in middle-aged adults: A double-blind, placebo-controlled, within-subjects trial. Nutr Neurosci. 2017;20(2):135-151.
41. Li X, Cai X, Ma X, et al. Short- and long-term effects of wholegrain oat intake on weight management and glucolipid metabolism in overweight type-2 diabetics: A randomized, control [sic] trial. Nutrients. 2016;8(9):549.
42. Mengeaud V, Phulpin C, Bacquey A, Boralevi F, Schmitt AM, Taieb A. An innovative oat-based sterile emollient cream in the maintenance therapy of childhood atopic dermatitis. Pediatric Dermatology. 2015;32(2):208-215.
43. Thongoun P, Pavadhgul P, Bumrungpert A, Satitvipawee P, Harjani Y, Kurilich A. Effect of oat consumption on lipid profiles in hypercholesterolemic adults. Journal of the Medical Association of Thailand. 2013;96(Suppl 5):S25-32.
44. Common oat for homeopathic preparations. In: French Pharmacopoeia. Saint-Denis, France: National Agency for the Safety of Medicines and Health Products; 2008.
45. Melzig M, Hiller K, Loew D. Avenae herba. In: Blaschek W, ed. Wichtl – Teedrogen und Phytopharmaka, 6th ed. Stuttgart, Germany: Wissenschaftliche Verlagsgesellschaft mbH; 2016:106-108.
46. Rhodes L, Bradley I, Zair W, Maxted N. Avena fatua. The IUCN Red List of Threatened Species. 2016:e.T172049A19394581. Available at: https://dx.doi.org/10.2305/IUCN.UK.2016-3.RLTS.T172049A19394581.en. Accessed July 14, 2022.
47. Rhodes L, Bradley I, Zair W, Maxted N. Avena sterilis. The IUCN Red List of Threatened Species. 2016:e.T172204A19395364. Available at: https://dx.doi.org/10.2305/IUCN.UK.2016-3.RLTS.T172204A19395364.en. Accessed July 14, 2022.