Nutrition - antioxidants - their role in racing - is there merit in specifically supplementing antioxidants to enhance performance?
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By Catherine Rudenko
Antioxidants are substances that slow down damage to organisms created by the presence of oxygen. The need for antioxidants is always there, in all species, increasing as exercise intensity and duration increase. Is there merit in specifically supplementing antioxidants to enhance performance?
The nature of antioxidants
There are many forms of antioxidants naturally present within the body and supplied through the diet. One key feature of antioxidants is that they are ‘team players’. No one antioxidant alone can maintain the system, and some will only function in the presence of another antioxidant.
The role of an antioxidant is to keep reactive oxygen species (ROS) or free-radicals created in the presence of oxygen at an optimum level. Oxygen is required for life, it is always present, but as an element, it is highly reactive and so can also have an adverse effect on the body. The reactivity of oxygen in the body produces ROS which cause damage to cellular components such as DNA, proteins and lipids of cell membranes. Some ROS also have useful cellular functions, and so the purpose of antioxidants is not to eliminate ROS altogether but to maintain a healthy balance. In general, antioxidants operate in two ways: either preventing the formation of an ROS or removing it before it can cause damage to a cell component.
Sources of antioxidants
There are multiple sources of antioxidants including vitamins, enzymes and nutrient derivatives. Other nutrients such as minerals, whilst not having antioxidant properties, are also involved as their presence is required for the functioning of antioxidant enzymes. Two key examples are zinc and selenium.
As with many body systems, the ideal healthy balance can often go awry. When the level of ROS present overwhelms the capacity of antioxidants present, the body experiences oxidative stress. There are three main reasons for a horse in training experiencing oxidative stress:
Increased exposure to oxidants from the environment
An imbalance or shortage in supply of antioxidants
Increased production of ROS within the body from increased oxygen metabolism during exercise
Oxidative stress is of concern as it can exaggerate inflammatory response and may be detrimental to the normal healing of affected tissues. Oxidative stress during strenuous exercise, such as galloping or endurance, is typically associated with muscle membrane leakage and microtrauma to the muscle. Oxidative stress is now understood to play a role in previously unexplained poor performance.
Dietary antioxidants photo: horse eating?
Given the demands of training and the regularity of intense exercise and racing itself, the use of dietary antioxidants is an important consideration. As antioxidants are generally best considered as a cocktail, it is necessary to give consideration to provision of nutrients and their derivatives across the total daily diet.
The majority of racing feeds will be formulated to provide a good cocktail of basic antioxidants or their supporting minerals. All feeds will contain vitamin E, selenium and zinc for example. Some, but not all, feeds will also provide vitamin C. The source of these nutrients may also differ; for example, some feeds will contain chelated zinc or organic selenium, which offer improved availability. The source of vitamin E will also vary—the majority being provided as synthetic vitamin E; but some will include natural sources of vitamin E, which is more effective.
TOP: Oxidative stress is now understood to play a role in previously unexplained poor performance.
Once a good base diet is in place, consideration for strategic use of individual antioxidants may then be warranted to further enhance the capacity of the body to mitigate the effects of ROS on the muscle. Three popular and commonly used antioxidants are vitamin E, vitamin C and more recently coenzyme Q10.
Vitamin E
As a lipid-soluble antioxidant, vitamin E provides defence against ROS in cells, playing an important role in maintaining integrity of cell membranes. Vitamin E is the most commonly supplemented antioxidant. There are established recommended daily intakes for vitamin E, typically 1000 IU per day for a horse in training; however, further supplementation beyond the basic nutritional requirement can yield benefits. Modern race horse feeds are well fortified—the majority providing upwards of 300 IU/kg, resulting in an average daily intake of over 2000 IU/day.
Intakes of above the base rate have been investigated for their effect on CK (creatine kinase) and AST (aspartate aminotransferase)—two markers of muscle damage. One such study used endurance horses whereby intakes ranged from 1150 IU up to 4750 IU per day. Elevated intakes of vitamin E correlated with lower levels of CK and AST suggest that vitamin E can affect muscle membrane permeability and injury to muscle during exercise.
As a guide to improving antioxidant capacity, an intake of up to 5000 IU per day would be appropriate for a horse in training. Vitamin E intake is influenced by the level of fats fed in the diet; and where additional oils are added, further vitamin intake E is required, as vitamin E will be utilised in stabilising the oil itself. Fats fed in a dry format, such as extruded rice bran, are normally fortified with vitamin E for this reason and do not require further supplementation.
Vitamin E is available in feeds and supplements in two forms: synthetic or natural. The natural form, d-alpha-tocopherol, is made up of a single isomer (chemical unit). The synthetic form, dl-alpha-tocopherol, is made up of eight different isomers—only one of which is molecularly the equivalent of natural vitamin E. The dose rate required to increase serum vitamin E levels in horses is lower for natural E than synthetic vitamin E.
The increased bioavailability of natural vitamin E has led to further research in comparing this source against synthetic vitamin E for efficacy against oxidative stress and physical gait changes. The study used 3 diets: a control diet with the standard recommended intake of 1000 IU/day provided by synthetic vitamin E; a higher intake synthetic vitamin E diet of 4000 IU/day; and a high intake of natural vitamin E at 4000 IU/day. The study lasted for six weeks and measured serum levels of vitamin E at various time points along with markers of oxidative stress, CK and AST levels, and gait analysis.
The key findings:
All diets increased serum vitamin E over time; however, the increase was not significant in the diet, providing only 1000 IU/day of synthetic vitamin E. The greatest difference in serum vitamin E was seen in the natural vitamin E diet where levels increased by 77.25% from day one to the last time point.
Oxidative stress was measured through multiple tests including oxidation of lipids (TBARS). Horses supplemented with natural E had lower levels of lipid oxidation markers than both synthetically supplemented horses at the second exercise test, which occurred after six weeks of fitness training.
AST levels were lower within the two hours post exercise of natural E supplemented horses compared to synthetic vitamin E horses; however, by 24 hours, the difference was no longer significant. There was no noted significant effect on CK.
Gait analysis before and after exercise showed better movement of horses that were supplemented with natural vitamin E. These horses experienced less of a reduction in their stride duration post exercise, potentially indicating less muscle soreness due to less oxidative stress.
As vitamin E is well proven to be an effective antioxidant, it may be tempting to think that ‘more is better’; however, as with all nutrients, there is a safety limit to consider. Current research indicates that supplementing at 10 times the base level—an intake of 10,000 IU/day—may result in poor bone mineralisation and impair beta-carotene (vitamin A) absorption. An intake of 4000-5000 IU/day based on the research above and other studies would appear effective whilst also being well below the presumed safety limit.
Vitamin C
Ordinarily horses can manufacture adequate vitamin C within the body, unlike humans that require direct supplementation. Additional vitamin C is required and often recommended when the body is challenged through disease or periods of stress. …
