Vitamin K3 (menadione) in Pet Food: Is It Safe?

One of the most popular fallacies that arises in discussions of pet health is the appeal to nature or naturalistic fallacy. Simply put, this is the notion that what is labeled “natural” is inherently safe, beneficial, or otherwise good, and what is labeled “artificial” is inherently unsafe, harmful, or bad. This argument fails on many levels. For one thing, the distinction between natural and artificial is often quite arbitrary and based on ideology rather than any rational criteria. How could any food crop, which consists of huge, bizarrely
mutated plants that could never survive without cultivation, be natural? For
that matter, how could most breeds of dog be considered natural when they have
been so dramatically altered in form and function by thousands of years of controlled breeding? Is wearing clothes, washing our hands with soap, cooking our food, or really any of the basic health and safety practices we follow routinely natural if we are the only species who employs them?

The appeal to nature fallacy also fails on the simple basis of being demonstrably untrue. Arguably natural things like Salmonella, hookworm, bubonic plague, and uranium are clearly dangerous. And clearly artificial things like vaccines, antibiotics, and modern sewage and water treatment systems are the only reason the majority of human beings gets to live past childhood these days. So whenever the only basis for declaring something
good or bad for your pets appears to be the idea that it is natural or artificial, it is wise to be very skeptical of such claims and look for more reliable evidence.

A perennial example easily found on the Internet is Vitamin K3 (menadione) in pet foods. Vitamin K is an essential nutrient needed in very low levels by dogs and cats. It is required for producing the substances that allow blood to clot and prevent us from bleeding to death from every little scratch. Most rat poisons consist of chemicals that interfere with Vitamin K, and these common and very dangerous poisons frequently lead to dogs coming into the veterinarian’s office with severe, uncontrollable bleeding. Fortunately, in
most cases these patients can be saved, and the cornerstone of their treatment
is Vitamin K replacement.

Most of the Vitamin K dogs and cats need is manufactured by bacteria in the gastrointestinal system and absorbed from there, so dietary requirements are miniscule. The one known exception is that cats fed diets with a high proportion of fish oil in them have developed Vitamin K deficiency and bleeding problems. Since fish as a protein source and fish oil as a supplement are becoming more widespread, it is possible that this problem could be seen more frequently. In general, however, the amount of dietary Vitamin K required by dogs and cats is still very, very small.

Plant and animal sources of Vitamin K include two types, Vitamin K1 and Vitamin K2. Vitamin K3, or menadione, is a synthetic form of Vitamin K. By itself, it has little biological activity, but it can be converted to a more active form by bacteria in the gut and other pathways. It is useful as a Vitamin K supplement in pet foods because it is more stable and tolerates heating better than the other forms of Vitamin K. Advocates of
“natural” medicine and nutrition often claim, however, that unlike these other forms, Vitamin K3 is toxic to dogs and cats. So what is the basis for this?

Of course, the first foundation “natural” medicine advocates use for claiming menadione is harmful and should be replaced with Vitamins K1 or K2 is the appeal to nature fallacy. As I’ve already pointed out, this is a meaningless claim which tells us nothing about the safety of any food or supplement. So what about other, more meaningful forms of evidence?

Well, to begin with, no case of toxic effects from menadione in commercial dog or cat food has ever been substantiated. Millions of pets have been consuming this vitamin for
decades, so if the supplement were to have any significant potential risk, one
would expect many documented cases of harm. This is, at least, the basis
“natural” medicine advocates use to claim that the herbal products and dietary supplements they recommend are safe. Unfortunately, without any systematic effort to monitor for such events the best we can say is that there does not appear to be a large or common risk, though we cannot rule out the possibility of some negative effects in some individuals solely on the basis that such cases have not been reported.

There is some laboratory research and pre-clinical animal studies that look at the safety of menadione. These have found that toxic effects can be seen on isolated cells, rats, and other animal models in the laboratory, but at levels tremendously higher than could ever be achieved by eating foods supplemented with Vitamin K3. This points out another common fallacy employed by so-called “holistic” medicine practitioners, the
notion that chemical compounds are inherently either toxic or safe. The reality
is that toxic effects are a function of the dose or amount of a substance one
is exposed to, the route of exposure, the individual’s susceptibility, and many other factors. Water and oxygen are toxic at high enough doses and under the right circumstances. And deadly natural poisons such as curare and other animal toxins can have beneficial medical uses if handled and dosed appropriately. So it is meaningless to simply label something as
“toxic” and ignore the devil in the details.

It turns out that doses of menadione needed to cause health problems are more than 1000 times greater than could be gotten through food supplementation, and the studies showing toxic effects usually involve injecting the vitamin into animals at high doses, not providing it in food in miniscule amounts. It is true that Vitamin K3 supplements for human use have been banned by the Food and Drug Administration (FDA), however this is because
of the potential for very large exposures when humans irrationally choose to take extreme quantities of dietary supplements. The FDA does permit the use of menadione in animal feeds because the consumers, our pets, are unlikely to make similar mistakes. When the toxic dose is more than can be found in an entire bag of food, the risk of accidental exposure to harmful levels is negligible.

Bottom Line
Under normal circumstances, dogs and cats need extremely small amounts of dietary Vitamin K. At the low levels of supplementation in commercial foods, menadione is a safe source of this Vitamin K. Toxic effects can be seen when enormous quantities are given to an animal or when menadione is used injectably, but there are no documented cases of any harmful effects from dietary supplementation of menadione in commercial pet foods. The three veterinary nutritionists and one veterinary toxicologist I consulted on this
issue all agreed that there is no evidence of any significant risk from menadione in commercial pet foods. The concerns about this supplement seem to stem almost entirely from the appeal to nature fallacy and from the mistaken belief that substances are inherently either safe or toxic regardless of dose or route of exposure.

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