Dangers of Vitamin E

Studies have recently found that people taking high-dose vitamin E supplements daily had an increased risk of dying, but equine nutritionists say we shouldn’t extrapolate that to horses.

Study lead author and internist Edgar R. Miller III, MD, PhD, associate professor of medicine at The Johns Hopkins University School of Medicine, says, "Our study shows that use of high-dose vitamin E supplements certainly did not prolong life, but was associated with a higher risk of death." In a report posted at CBSNews.com Miller says the risk of death starts to increase at 150 IU daily, but at 400 IU, the typical dose available in vitamin E capsules, the risk of dying from any cause is about 10% higher than for people not taking the vitamin. At 2,000 IU of vitamin E, the risk increased more than 20%.

Adds Raymond Gibbons, MD, a Mayo Clinic cardiologist and chairman of the American Heart Association conference where the study was reported, "Too often in terms of the supplements, there's very scant science. In this area, we have the science. Vitamin E doesn't work."

However, Carey A. Williams, PhD (equine nutrition), equine extension specialist and assistant professor in the department of animal science at Rutgers University, who has studied the effects of vitamin E in horses, says, "I don't think we can use the Hopkins study as a connection to our industry at all."

The human study was based on analysis of raw data from 19 major clinical trials involving more than 136,000 patients, sorted by whether high- or low-dose levels of vitamin E were taken. However, most of the patients in the trials were over 60, and a majority had pre-existing conditions such as heart disease, so the study’s application to younger, healthy adults might be limited, the Hopkins researchers noted.

What Does This Mean for Horses? 
States Sarah Ralston, VMD, PhD, Dipl. ACVN, associate professor of animal science at Rutgers University, "I have been worried about the current mania to give over 2000 IU vitamin E to all sorts of horses, based on limited if any evidence that it is even effective. While vitamin E is generally thought to be safe, excessive amounts may interfere with other fat-soluble vitamin absorption, and the effects of huge doses in horses have not been documented. However, we should not extrapolate a single (and somewhat flawed) human study to alarm the horse-owning public!"

Williams, who has studied the effects of vitamin E in horses, says, "Many studies of vitamin E in healthy and diseased humans has been shown to be safe up to 3,200 IU, and these studies were controlled for up to five years! However, the studies I have performed in healthy, exercising horses found benefits of Vitamin E use between the ages of three and 12 years old."

"The majority of horses that are recommended to have 5,000 IU a day of vitamin E are intensely exercising horses that are prone to muscle soreness and/or damage and have immune systems that may be compromised by the stress of heavy exercise," she adds. "The moderately working horse generally is recommended around 2,500 IU a day. Most other lightly working or maintenance horses wouldn't normally need extra supplementation of vitamin E unless they are on limited pasture or a poor-quality hay. So I definitely agree with Dr. Ralston's statement, 'I think the maximum safe dose for the average horse would be no more than 2,000 IU/day.' I would just emphasize average horse.

"I think Dr. Ralston and I both agree that the Hopkins study, in and of itself, is no grounds for dire predictions for the horse," continues Williams. "Keep in mind this study was not a direct cause and effect study and only looked at correlations from previous studies on unhealthy individuals. I would assure horse owners that they should not stop supplementing with vitamin E."

About the Author

Marcia King

Marcia King is an award-winning freelance writer based in Ohio who specializes in equine, canine, and feline veterinary topics. She's schooled in hunt seat, dressage, and Western pleasure.

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