CHAPTER 20 Herbs and Nutraceuticals
Herbal medicine, also called phytomedicine, is the use of therapeutic plants, plant parts, or plant-derived substances to aid in fighting against infections and diseases or enhancing overall health. In the United States, the herbal market exceeds $3.2 billion in sales, and 32% to 37% of Americans use herbal agents each year. This percentage is thought to be much higher in Europe, where herbal agents are more widely accepted by medical professionals. In 2005 the United States herbal market value was thought to be higher than in previous years, with garlic and echinacea being the two top-selling herbs. A United States Department of Agriculture (USDA) study revealed that approximately 70% of U.S. horse operations fed some type of supplement and that nearly 5% of those operations fed herbal supplements.
The word nutraceutical comes from the words nutra, meaning nutrient, and ceutical, or pharmaceutical, meaning a medical drug. Nutraceuticals are defined by the Foundation for Innovation in Medicine (1991) as “any substance that may be considered a food or part of a food and provides medical or health benefits, including the prevention and treatment of disease.” Nutraceuticals can include nutrients such as vitamin E or derivatives of nutrients such as glucosamine or herbs.
This chapter focuses on herbs and other nutraceuticals that are commonly used in the horse industry. Published literature, however, is scarce on this front, so research in human and other species is included to illustrate better the possible benefit of the supplements. This should not be interpreted to mean that the supplements are of value in the horse until equine-specific research is performed. Research findings in human and laboratory animal literature do not necessarily coincide with findings in the equine species.
Herbal supplements that affect the immune system can be classified as adaptogens, immunostimulants, or both. Adaptogens increase resistance to physical, chemical, or biological stressors, whereas immunostimulants activate nonspecific or innate defense mechanisms against viral, bacterial, or cellular infections. Most of the studies to date in laboratory animals, humans, and other species have determined that herbal supplements do not enhance the normal immune response but may help if the immune system is compromised. Many of these effects of herbal supplements and nutraceuticals also depend on the source and processing of the supplement. Various products are available as extracts, powders, and teas, and all have different efficacies. Efficacy also varies with the portion of the plant that is used, whether it is bark, leaves, berries, or roots. The active components, actions, drug interactions, and equine research information pertaining to some of the herbs described later have been summarized (Table 20-1).
The topic of safety is of utmost importance. It is believed by many that, because herbs are “natural” products, they are safe; however, various herb toxicities and negative side effects indicate that this is a dangerous misbelief. Herbs have druglike actions that can interact with other components in the horse’s diet and with medications. Some herbs contain prohibited substances like salicylates, digitalis, heroin, cocaine, and marijuana. Drug-herb interactions can create effects ranging from mild to severe and thus should be taken into account when determining which “natural” product to use. Other herbs that are nontoxic in some species may be toxic to equids; some of these include St. John’s wort (Hypericum perforatum), castor bean plant (Ricinus communis), mistletoe (Phoradendron flavescens), and cherry trees (all species, Prunus serotina).
Administration of some of these products can lead to banning by competition and racing organizations. In the United States, most breeds and competitions operate under U.S. Equestrian Equine Drug Testing Rules, whereas most international competition falls under International Federation for Equestrian Sports (FEI) rules. The following excerpt is from the United States Equestrian Federation (USEF) Drugs and Medications Guidelines (2006):
Just some of the examples of the hundreds and perhaps thousands of examples of herbal/natural or plant ingredients that would cause a product to be classified as forbidden are valerian, kava kava, passionflower, skullcap, chamomile, vervain, lemon balm, leopard’s bane, night shade, capsaicin, comfrey, devil’s claw, hops, laurel, lavender, red poppy, and rauwolfia. Trainers, owners, exhibitors, and their veterinarians are cautioned against the use of medicinal preparations, tonics, and powders, and products of any kind, including those used topically, the ingredients and quantitative analysis of which are not specifically known, as they might contain a forbidden substance. This is especially true of those containing plant ingredients.
Valerian components prolong the action of barbiturates in laboratory animal species and can interact with alcohol. They also inhibit cytochrome P450, the body’s major detoxification enzyme, which can lead to multiple drug interactions if not used with caution. These actions were enough to prompt USEF and the FEI to ban valerian-containing products. Persistent use of echinacea causes hepatotoxic effects in species other than horses, and the compound should not be administered concurrently with other drugs. Garlic can cause Heinz body anemia in horses and also causes gastrointestinal upset, allergic reactions, and dermatitis in humans. Garlic also decreases systolic and diastolic blood pressure; however, there is insufficient evidence to recommend its use for treatment of hypertension in humans. Ginger inhibits thromboxane synthetase and increases bleeding time in laboratory animals, which could be detrimental if used with anticlotting drugs like warfarin. Some of ginseng’s adverse effects in humans include hypertension, insomnia, vomiting, headache, nervousness, sleeplessness, and epistaxis. When ginseng is administered, it is advisable to discontinue use of warfarin, heparin, aspirin, and other nonsteroidal anti-inflammatory drugs (NSAIDs).
Devil’s claw (Harpagophytum procumbens) is reported to have an anti-inflammatory effect in humans and laboratory animals. On the animal health market, devil’s claw is primarily used for its painkilling and anti-inflammatory properties, and there are many testimonials for its use in humans for relief from rheumatism and other joint disorders. The active ingredients are various iridoid glycosides, acetylated phenolic glycosides, and terpenoids. Alleviation of lower back pain has been reported in humans taking devil’s claw extracts containing more than 50 mg of harpagoside (a glycoside) per day. Most of the clinical studies in humans, some of which were blinded, revealed decreased pain intensity and increased flexibility in patients taking devil’s claw extract.
Studies in laboratory animals have revealed that topical application of devil’s claw decreases expression of cyclooxygenase-2, which is a rate-limiting enzyme involved in the inflammatory cascade. In the only known study involving horses with osteoarthritis, the effects of a proprietary polyherbal composite joint supplement containing devil’s claw were evaluated. An anti-inflammatory effect was observed in association with a reduction in prostaglandin E2 content in synovial fluid. In my opinion, sufficient evidence exists for further testing of devil’s claw for equine use. There is, however, a potential for devil’s claw to cause gastric ulcers, but other drug interactions have not been reported.
Echinacea (Echinacea spp.) is a common immunostimulant that is reported to have anti-inflammatory and antioxidant properties. It is taken by humans to help fight colds. In horses, echinacea is typically used as an immune booster to complement a healthy immune system. It is generally recommended that animals be supplemented with echinacea at the first signs of illness or infection. If administered too late in the cycle, the herb will be less effective.
Echinacea purpurea, E. angustifolia, and E. pallida have been studied for their medicinal properties and are reported to have a wide range of benefits. The common active components of Echinacea spp. include polysaccharides, glycoproteins, alkamides, and cichoric acid, which is a derivative of caffeic acid. However, depending on the species of plant and method of commercial preparation, the concentrations of these components will vary greatly.
In horses supplemented with echinacea for 42 days at a level equivalent to 1000 mg of standardized extract, lymphocyte count increased and neutrophil count decreased at day 35 of the 42-day supplementation period, but the clinical relevance of these findings is unknown. Increases in red blood cell count and hemoglobin were also seen, which demonstrates the potential for echinacea to be used in horses as an immune booster and to increase oxygen-carrying capacity. More research should be completed to elaborate on these preliminary observations.