Antioxidants and Sled Dogs
by Kenneth W. Hinchcliff, M. Hayek and G. Reinhart
There is increasing awareness of the need for protection against oxidant stress in humans and animals. Oxidant stress and damage occur as an inevitable consequence of the use of oxygen. The greater the rate at which oxygen is used, the greater the rate of production of free radicals and other oxidant substances. If not neutralized by the body, these free radical and oxidant substances cause oxidation (damage) of important cellular and subcellular structures such as proteins, cell membranes and genes. Damage of these structures may result in damage to certain tissues and cause disease.
Alaskan sled dogs are at increased risk of oxidant damage because of their high rate of oxygen consumption during exercise and because of the prolonged duration of the exercise that they perform. Oxidant damage may also be exacerbated by the high fat diet of these dogs, especially if there is any rancidity of dietary fats. It has been well demonstrated that moderate exercise (running 40-50 miles/day for 3 consecutive days) results in oxidative stress and damage in Alaskan sled dogs (Hinchcliff et al 2000, Baskin et al 2000, Piercy et al 2000a). Provision of antioxidants such as Vitamin E and carotenoids diminishes the degree of oxidant damage during exercise (Baskin et al 2000) although it does not decrease the incidence or severity of exercise-induced muscle damage (Piercy et al 2000a, Piercy et al 2000c). Furthermore, dogs with higher serum vitamin E concentrations (above approximately 40 ug/ml) are twice as likely to finish the Iditarod Trail Sled Dog race as are dogs with serum vitamin E concentrations below this value (Piercy et al 2000b). Serum concentrations of vitamin E of 40 ug/ml are usually achieved by supplementation of the diet of sled dogs in training and racing with 400 IUs of medical grade vitamin E (alpha tocopherol) daily, preferably at the time high fat meal is fed to maximize absorption. We, therefore, recommend that the diet of sled dogs in training be supplemented with 400 IUs of medical grade vitamin E once daily.
It should be noted that incorporation of vitamin E into tissue membranes and cells is not immediate after starting supplementation. It is likely that tissued concentrations of vitamin E require some time to increase after beginning supplementation. We, therefore, recommend the vitamin E supplementation of the diet of sled dogs begin at the start of the training season and continue throughout the season. Because exercise such as racing acutely decreases concentrations of vitamin E in blood (Hinchcliff et al 2000, Piercy et al 2000a, Piercy et al 2000b), we strongly recommend that vitamin E supplementation be continued during racing.
There is no evidence at present that higher levels of supplementation (ie, above 400 IU per day) are required. In fact, there is concern, based on observations in greyhounds and humans, that excessive supplementation may cause defects in the ability of the blood to clot. Another concern regarding vitamin E supplementation is the source of the vitamin. The supplement should be medicinal (human) grade and be provided daily as the sole supplement. Vitamin E should not be supplemented as a concoction with other fat soluble vitamins (especially vitamins A and D). Mixtures of fat soluble vitamins often contain low concentrations of vitamin E when compared to concentrations of vitamin D. Hence, dosing with these mixtures to provide the recommended intake of vitamin E may result in the ingestion of toxic amounts of vitamin D. Vitamin D, in excessive amounts, is very toxic and may cause severe and debilitating disease.
Oxidant Damage Induced by Exercise in Alaskan Sled Dogs
by Kenneth W. Hinchcliff, Gregory A. Reinhart, Robert DiSilvestro, Arleigh Reynolds, Richard Swenson and Ashley Blomstein Fujii
Exercise imposes an oxidative stress in many species. The oxidant stress is imposed because the use of oxygen in metabolism results in the production of reactive oxygen species, such as hydroxyl radicals. The greater oxygen consumption that occurs during exercise presumably increases the amount of these reactive oxygen species. The reactive oxygen species, so called free radicals, are absorbed by antioxidants such as vitamin E, glutahione and antioxidant enzymes. Recently, we examined the effect of 3 consecutive days of exercise on an index of oxidant stress, the plasma isoprostane concentration, and on serum vitamin E and other antioxidant substances. Exercise was associated with a significant decline in serum vitamin E concentration, an increase in plasma isoprostane concentration, and an increase in serum creatine kinase activity. Whether the reduction in serum vitamin E concentration was causally associated with the change in serum CK activity is unknown. However, these results do suggest that exercise is associated with oxidative stress in dogs, and that repetitive exercise may result in consumption of body antioxidant reserves.