*Hill's Pet Nutrition, Inc. Science and Technology Center
Topeka, Kansas, US
The skin is the largest organ of the body and is uniquely challenged by oxidants due to its role as a barrier between the body and its environment. It is exposed to high oxygen tension, and has a high lipid content in the stratum corneum. Vitamin E is a chain-breaking antioxidant that prevents the propagation of free-radical reactions. Therefore, lipophilic antioxidants such as vitamin E are expected to play a major role in scavenging reactive oxygen species during oxidative stress. The primary purpose of this study was to determine the effect of feeding foods with varying levels of vitamin E on serum and skin vitamin E concentrations in dogs and cats.
All protocols were approved by the Hill's animal use and care committee and complied with USDA guidelines for use of laboratory animals. Dogs and cats were stratified into two groups per species based on vitamin E concentrations in the skin, gender, and body weight. One group of 10 dogs was fed a dry food with 217 IU total vitamin E/kg of food (low E dog food). The other group of 10 dogs was fed a different dry food with 654 IU total vitamin E/kg of food (high E dog food). One group of 10 cats was fed a dry food with 86 IU total vitamin E/kg of food (low E cat food). The other group of 10 cats was fed a different dry food with 709 IU total vitamin E/kg of food (high E cat food). These foods were fed for eight weeks. Food was fed to maintain body weight based on weekly weight recordings. Blood and skin vitamin E were measured initially and at the end of the study.
There were no significant differences in serum or skin vitamin E concentrations between the dietary groups for either species at the beginning of the study. Initial and final serum concentrations of vitamin E in both species were increased (P<0.05) in the groups receiving the high E food, but not the low E food. Serum vitamin E values generally decreased slightly from beginning to the end of the study in dogs and cats fed the low E food. At the end of the study, vitamin E concentrations in skin were significantly (P<0.05) influenced by initial skin vitamin E concentration, body surface area, and final serum vitamin E concentration. When these variables were accounted for, species did not effect final skin vitamin E concentration.
The results of this study reveal that increasing vitamin E levels in food significantly increases vitamin E concentrations in serum and skin. As the outermost barrier of the body, the stratum corneum is frequently and directly exposed to a pro-oxidant environment. Vitamin E is the major antioxidant in stratum corneum, and is an early and sensitive biomarker of environmentally induced oxidation. Therefore, antioxidant defenses are highly dependent upon adequate nutrition and increasing levels of dietary
Vitamin E in foods for dogs and cats has the benefit of enhancing oxidative defense in the skin.