The Controversy Over Menadione in Dog Food

Some call menadione a dog food necessity. Others reject it as a dangerous toxin. So, what is menadione? And why is it used in some dog food recipes and not others?

Menadione is actually a vitamin. It’s the manmade version of an essential nutrient commonly known as vitamin K — or more precisely, vitamin K3.

K3 is just one of three known versions of vitamin K:

• Vitamin K1 – naturally found in green leafy vegetables
• Vitamin K2 – produced by bacteria living inside a dog’s gut
• Vitamin K3 – menadione, the synthetic version

Vitamins K1 and K2 are considered natural and fat-soluble. They’re active and chemically ready to be used by the body just as they are.

However, vitamin K3 is synthetic. And all forms of the vitamin K3 must undergo the cellular process of alkylation before they can be used by the body.¹ Alkylation occurs through gut bacteria or tissue enzymes modifying the vitamin structure by adding side chains, making the vitamin active and ready to be used by the body.

What’s so important about Vitamin K?

The key role of vitamin K in the body is in controlling blood clotting. Without the blood’s ability to clot there are numerous issues relating to bleeding, aneamia, and hemorrhage which can occur in the body. Vitamin K is also important in bone formation and other bodily systems.

So, how much vitamin K does a dog need?

It is more difficult to measure how much vitamin K is needed compared to other vitamin requirements, because of gut bacteria providing a supply of vitamin K2. That being said, studies on vitamin K deficiency in adult dogs show that they need about 2-5 micrograms per kilo of body weight per day. And most of the vitamin needed is actually produced by bacteria living within the intestines.

Vitamin K is so readily available to dogs that there’s no AAFCO minimum for vitamin K in dog food. Deficiencies of vitamin K have only been seen in dogs as a result of other factors, such as liver disease, severe blood loss or anticoagulant use.

Menadione — a nutritional necessity?

The controversy over menadione appears to be driven by two opposing views.

Supporters tend to see menadione as a necessary supplement that dog food manufacturers should include in their recipes.

As vitamin K is so available, however, why do manufacturers add it at all?

Simply put it’s because the amount of vitamin K2 that’s available to a dog through the work of their gut bacteria isn’t the same across individuals. Different dogs will receive different quantities of vitamin K2. Furthermore, the amount of vitamin K1 available through eating green, leafy vegetables, like broccoli, varies too. Like all nutrient levels of vegetables, the levels found can vary widely dependent on growing and storage conditions. The location they were grown, the soil, the weather, the time of harvesting and so many other factors all affect the nutrient levels found. Plus storage conditions, and the freshness of the vegetables affect the nutrients levels too. Vitamin K1 would be degrading over time and with exposure to various conditions or other nutrients.

In short, a manufacturer can’t be certain your dog will be getting their 2-5 micrograms of vitamin K per day. So they add it out of caution.

This aligns with the advice of the National Research Council (the body that AAFCO nutritional profiles are based on), who suggest that adding a precautionary 22 micrograms of menadione per kilogram of body weight to diets for adult dogs, and twice that for growing puppies is recommended for complete diets.

Advocates of vitamin K3 also argue that menadione is considered safe because toxic levels are more than one thousand times greater than the recommended daily dose. This is verified by both the National Research Council Nutrient Requirements of Dogs and Cats (NRC, 2006) and the Vitamin Tolerances of Animals (1987).

As neither vitamin K1 nor vitamin K2 are approved for use in pet food, menadione really is the only option for pet food manufacturers who want to supplement the vitamin K content of their diets.

So, what’s the controversy?

Critics argue that vitamin K3 is toxic and connected with allergic reactions, anaemia and liver damage. However, there are two things to say about this:

First, there have been no reports of nutritional toxicity or harm in dogs and cats (not to mention its extensive use in pig and poultry diets) over the more than 50 years in which menadione has been used.

Second, the National Research Council and the Vitamin Tolerances of Animals both state that Vitamin K toxic levels are more than 1000 times greater than the recommended daily dose.

Is Vitamin K3 potential toxin?

Critics see menadione as a precursor to the vitamin’s more natural versions. They cite (mostly human) studies that make a number of unsettling claims. They worry that menadione can…

• Promote allergic reactions⁶
• Weaken the immune system
• Cause toxic reactions in liver cells⁷
• Induce hemolytic anemia (red blood cell toxicity)⁸

It is worth noting however that none of these studies are relating to dietary menadione.

One company selling menadione warns its human buyers that menadione is “toxic to kidneys, lungs, liver, mucous membranes. Repeated or prolonged exposure to the substance can produce target organ damage.”⁹

Seeing warnings around massively concentrated nutrient sources such as vitamins when available for purchase is, however, completely normal. Any fat soluble vitamin taken in excess has the potential to cause toxicity diseases. This is not specific to Menadione, but cautions which are necessary as a part of the safety information and directions for use of many nutrients available as a concentrated source.

Is Menadione unsuitable for treating Vitamin K deficiency?

According to a peer-reviewed article published in 2004 by the Linus Pauling Institute at Oregon State University:[1. Jane Higdon, PhD, Linus Pauling Institute, Oregon State University (2004); updated Victoria Drake, Ph.D., Linus Pauling Institute, Oregon State University (2008), peer-reviewed by Sarah Booth, Ph.D., Director, Vitamin K Research Program, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Vitamin K and the Newborn Reviewed by Dennis T. Costakos, M.D. F.A.A.P., Franciscan Skemp Healthcare-Mayo Health System, Mayo Medical School]

“Although allergic reaction is possible, there is no known toxicity associated with high doses of the phylloquinone (vitamin K1) or menaquinone (vitamin K2) forms of vitamin K¹⁰.

The same is not true for synthetic menadione (vitamin K3) and its derivatives.

Menadione can interfere with the function of glutathione, one of the body’s natural antioxidants, resulting in oxidative damage to cell membranes.

Menadione given by injection has induced liver toxicity, jaundice, and hemolytic anemia (due to the rupture of red blood cells) in infants¹¹; therefore, menadione is no longer used for treatment of vitamin K deficiency¹².

No tolerable upper level of intake has been established for vitamin K.”

If we think about menadione, and its need for alkylation or activation by gut bacteria or tissue enzymes, it makes sense that injecting menadione into the blood stream directly would be ineffective. The toxic level when injected, is lower, at around 100 times the nutritional requirement, but this is unrelated to the safety of dietary menadione.

How does Menadione appear on packaging?

AAFCO Official Publication (2024) lists only three sources of vitamin K3 which are approved for use. These are:

• menadione dimethylpyrimidinol bisulfite (MDPB)
• menadione nicotinamide bisulfite (MNBS)
• menadione sodium bisulfite complex (MSBC)

The bottom line

Like any fat-soluble vitamin, when used in very large amounts, menadione can be toxic.

However in small doses, like those used in commercial dog food, menadione is safe and ensures that a dog’s nutritional requirement for vitamin K is met.

As vitamin K is a widely available vitamin, which is not commonly found to be deficient, it comes down to a personal preference whether you prefer to avoid menadione in your dog’s diet, or whether you’re happy that the pet food manufacturers are being thorough in their inclusion of of a vitamin K source, and not simply assuming that your dog’s nutritional requirements for vitamin K are being met elsewhere.