Potential Vitamin K Supplement Eyed for Equine Bone Health

A group of Japanese researchers have suggested a particular form of vitamin K could be a potential candidate for increasing equine bone density while decreasing breakdown, thus improving overall bone health. However, veterinarians caution that this is not a viable supplementation route to pursue until further research on the effects of vitamin K on horses is completed.

Vitamin K is a fat-soluble vitamin that plays an important role in blood clotting, bone metabolism, and vascular health.

"Although no direct studies on the effect of vitamin K on bone health in horses have been conducted, studies in humans and rodents indicate that vitamin K can increase bone formation and decrease bone resorption (breakdown)," said Tohru Matsui, PhD, who led a research team at Kyoto University's Division of Applied Biosciences that examined vitamin K in the bloodstream of horses.

Based on the studies in other species, the researchers suspect that vitamin K regulates bone metabolism to presumably assist in the formation of strong bones.

"There are three main types of vitamin K: phylloquinone, menaquinones, and menadione," he said, adding that not all types of vitamin K are equal in their ability to promote bone health.

"(Cell culture) studies suggest that menaquinone-4 is the most potent vitamin K for regulating bone metabolism in humans and rodents," relayed Matsui, referring to the effects of the vitamin K type in in vitro studies in petri dishes.

The team set out to determine if any of the common forms of vitamin K could increase vitamin K levels in horses' blood and to assess the potential use of these forms as nutritional supplements. Matsui and colleagues divided 16 Thoroughbred racehorses into four different groups; three groups were fed 58 µmol/day of phylloquinone, menaquinone-4, or menadione for seven days. The fourth group served as the control and did not receive a supplement.

Researchers measured phylloquinone, menaquinone-4, and menadione plasma (blood) concentrations before supplementation and two, four, and eight hours after the last feeding on Day 7 to see which levels increased subsequent to supplementation.

Key findings of the study included:

  • Plasma phylloquinone concentrations quadrupled in the horses supplemented with phylloquinone;
  • Plasma menaquinone-4 levels in horses supplemented with menaquinone-4 remained unchanged; and
  • Menaquinone-4 plasma levels were significantly higher in the horses supplemented with menadione than with any other form of vitamin K.

Despite the fact that menaquinone-4 is believed to be the most potent form of vitamin K, supplementation with that form of vitamin K did not result in increased levels in the bloodstream; among the three forms only menadione supplementation increased menaquinone-4 levels. This finding prompted Matsui to note that it seems that horses metabolize the various types of vitamin K differently than other species.

Based on the increased levels of menaquinone-4 in the blood that resulted from menadione supplementation, the researchers concluded that, "Menadione is converted to menquinone-4 in horses, making menadione the best source of vitamin K for bone health in horses."

Before veterinarians can recommend supplementing with menadione, though, it's important to understand that more live-horse and laboratory research is needed on the effects of vitamin K supplementation on equine bone metabolism, as an overdose of the vitamin could be toxic.

The National Research Council, author of Nutrient Requirements of Horses, sixth edition states that the dietary vitamin K requirements have not been determined for the horse. Vitamin K deficiencies in horses have not been identified.

Carey Williams, PhD, an equine extension specialist and assistant director of extension at the Equine Science Center at Rutgers University, added, "I don't really recommend adding any extra to the diet because it can become toxic if not careful. Most diets--if they are balanced for the major nutrients--will have plenty of vitamin K and I don't see it necessary for extra supplementation."

The study, "Plasma vitamin K concentration in horses supplemented with several vitamin K homologs," was published in the Journal of Animal Science in April 2011. The abstract is 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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