Essential oils often evoke thoughts of scented candles and day spas, but their benefits beyond relaxation are less well-known. Essential oils are ultimately just plant extracts—and those are used in countless cleaning and personal-care products, and are the main ingredient in some pest-control products and some over-the-counter medications, like Vick’s VapoRub and some lice sprays. They’re used in the food industry because of their preservative potency against foodborne pathogens—thanks to their antimicrobial, antibacterial, and antifungal properties. Various oils have also been shown to effectively treat a wide range of common health issues such as nausea and migraines, and a rapidly growing body of research is finding that they are powerful enough to kill human cancer cells of the breast, colon, mouth, skin, and more.
A handful of promising, real-life studies have been conducted with humans and other animals, though most of the research in that realm thus far has been conducted in the lab. More controlled trials will be required before some of these applications will be available to the public, but meanwhile, scientists have turned up exciting results in another area of use: countering the growing antibiotic-resistance crisis. “The loss of antibiotics due to antimicrobial resistance is potentially one of the most important challenges the medical and animal-health communities will face in the 21st century,” says Dr. Cyril Gay, the senior national program leader at the United States Department of Agriculture’s (USDA) Agricultural Research Service.
As Cari Romm previously reported, livestock consume up to 80 percent of the antibiotics used in the U.S., and the amount actually jumped by 16 percent between 2009 and 2012, according to a recent FDA report. This rampant use of the drugs has led to “superbugs” that are becoming increasingly resistant to the antibiotics that are used to treat not just farm animals, but humans as well. In fact, almost 70 percent of the antibiotics given to these animals are classified as “medically important” for humans. According to Romm, “In the U.S., antibiotic resistance caused more than two million illnesses in 2013, according to a report by the Centers for Disease Control and Prevention, and an estimated 23,000 deaths,” and they’ve also amounted to an extra $20 billion in healthcare costs. And it’s only poised to get worse: a recent report commissioned by the U.K. government estimates that drug-resistant microbes could cause more than 10 million deaths and cost the global economy $100 trillion by the year 2050.
Numerous recent studies—including several done by the USDA—have shown great promise in using essential oils as an alternative to antibiotics in livestock. One of their studies, published in October 2014 in the journal Poultry Science, found that chickens who consumed feed with added oregano oil had a 59 percent lower mortality rate due to ascites, a common infection in poultry, than untreated chickens. Other research, from a 2011 issue of BMC Proceedings, showed that adding a combination of plant extracts—from oregano, cinnamon, and chili peppers—actually changed the gene expression of treated chickens, resulting in weight gain as well as protection against an injected intestinal infection. A 2010 study from Poultry Science produced similar findings with the use of extracts from turmeric, chili pepper, and shiitake mushrooms. A multi-year study is currently underway at the USDA that includes investigations into the use of citrus peels and essential oils as drug alternatives.
Researchers have also directly compared the effects of commonly used antibiotics with those of various essential oils. One such study, from the March 2012 issue of the Journal of Animal Science, found that rosemary and oregano oils resulted in the same amount of growth in chickens as the antibiotic avilamycin, and that the oils killed bacteria, too. Additional findings have shown that essential oils help reduce salmonella in chickens, and another study found that a blend of several oils can limit the spread of salmonella among animals. One of the co-authors of that study, Dr. Charles Hofacre, a professor at the University of Georgia’s College of Veterinary Medicine, says it’s such a new area of research that they don’t yet know exactly how the essential oils work, but “there is some strong evidence that they are functioning by both an antibacterial action in the intestine and also some have an effect to stimulate the intestinal cells ability to recover from disease more quickly–either by local immunity or helping keep the intestinal cells themselves healthier.”
In the lab, scientists have been testing all kinds of combinations of essential oils and antibiotics, and they’re repeatedly finding that the oils—used on their own and in combination with some common antibiotics—can fight numerous human pathogens, including antibiotic-resistant strains of E. coli, Staphylococcus aureus(which causes staph infection), and other common types of bacteria. Results consistently show that combining essential oils and antibiotics significantly lowers the amount of antibiotic required to do the job. For example, two recent studies showed that lavender and cinnamon essential oils killed E. coli, and when combined with the antibiotic piperacillin, the oils reversed the resistance of the E. coli bacteria to the antibiotic. Another recent study found that basil oil and rosemary oil were both effective in inhibiting the growth of 60 strains of E. coli retrieved from hospital patients. Other research has produced similar results for many other essential oils, both alone and in combination with antibiotics. Researchers believe that one mechanism by which the oils work is by weakening the cell wall of resistant bacteria, thereby damaging or killing the cells while also allowing the antibiotic in.
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