High Doses of Vitamin E Benefit Older Horses

Very high doses of vitamin E appear to benefit older horses' immune systems and could be an inexpensive means of battling "immunosenescence"--the decline in immune function because of the aging process.

"Horses have an increased susceptibility to infection because of a decline in immune function with advancing age," said Katherine Petersson, PhD, animal scientist and assistant professor at The University of Rhode Island.

Since vitamin E is known to play a key role in immune system function, Petersson's research team evaluated the effect of vitamin E on horses' immune function and response to vaccination against West Nile virus.

Sixteen older horses with an average age of 18.9 years were studied. Horses in the treatment group were supplemented once daily with 15 IU vitamin E/kg body weight--15 times the amount recommended in the NRC (2007 Nutrient Requirements of Horses). Blood was collected every two weeks for 16 weeks and all horses were vaccinated with a recombinant West Nile virus (WNV) vaccine at weeks seven and 14.

Compared to the control horses:

  • Vitamin E blood levels were significantly higher in supplemented horses;
  • Bacterial killing ability of white blood cells (i.e., monocytes and neutrophils) was increased in supplemented horses;
  • Blood levels of immunoglobulins IgGa and IgGT were higher in supplemented horses whereas IgGB concentrations were lower;
  • Supplemented horses had similar amounts of IgM; and
  • The (neutralizing) antibody response to the WNV vaccination was the same as supplemented horses.

Together, these results indicate that vitamin E impacts several key components of immune function--both humoral and cell-mediated--differently, relayed the author.

"The bottom line is that some indices increased, some decreased, and some remained the same across both cell mediate and humoral immunity," concluded Petersson.

However, before running off to buy that industrial sized vat of vitamin E, it is important to recognize that not all researchers support the use of high doses of vitamin E in horses.

Carey Williams, PhD, equine extension specialist and assistant professor at the Equine Science Center at Rutgers University, cautions, "Even though the study authors suggested that vitamin E supplementation may be an inexpensive, beneficial way of enhancing immune systems of older horses, potentially offering protection from disease and infection, they did advise that more research was needed. It is important to note that other studies using mega-doses of vitamin E in horses showed an interference with beta-carotene absorption, so supplementing at these high doses needs to be done with caution." (Read more from a previous article on TheHorse.com.)

Petersson, however, suggests that recommending against high levels of vitamin E supplementation are premature, but adds, "More research is certainly warranted."

The study, "The influence of vitamin E on immune function and response to vaccination in older horses," will appear in an upcoming edition of the Journal of Animal Science.

The abstract is currently available on PubMed.

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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