Researcher Cautions Against High Doses of Vitamin E

Vitamin E is the most commonly supplemented antioxidant in horses. It is a fat-soluble vitamin that is also currently employed in the routine treatment of horses with neurological diseases (affecting the brain and spinal cord).

In response to "Vitamin E and Horse Health: Myth or Miracle?" equine extension specialist and assistant professor Carey Williams, PhD from the Equine Science Center at Rutgers, The State University of New Jersey pointed out data published in 2006 that suggests vitamin E may not be completely safe at high doses.

"Vitamin E is widely considered safe even at 10,000 units per horse per day, which is 10 times the currently recommended dose by the National Research Council and the current recommended dose for neurologic horses," explained Williams.

But in Williams' study, horses fed 10,000 units of vitamin E daily may not benefit from the anti-oxidant properties of vitamin E as originally thought.

"More importantly, horses fed these high doses of vitamin E had lower beta-carotene (a precursor to vitamin A) than horses supplemented with much lower doses," said Williams.

A decrease in beta-carotene absorption, if great enough, could potentially lead to a vitamin A deficiency, in which case the classical sign is night blindness. Less well-studied deficiency symptoms include a decrease in immune function and reproductive problems.

More information is available in the study, "Oral vitamin E supplementation on oxidative stress, vitamin and antioxidant status and intensely exercised horses" published in the Equine Veterinary Journal Supplement #36.

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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